University of Maine Gases Point of The Experiment Lab Report

Description

Items expected in your report:
A header must be included with your name, your lab partner’s name, the date the experiment was performed, and a lab title.
It should give a brief description of the importance of the experiment and procedures. Essentially this is an objective. What was the point of the experiment?

It should include any changes to the procedure not included in the lab notebook. Otherwise, students must write “Procedures followed as written in the lab notebook.”

It should include any tables and graphs (appropriately labeled) and a one-sentence description of what the figure is showing.
It should include a brief analysis of the results. The analysis should describe any trends exhibited in the data, what the data shows/indicates/proves, and anything you find noteworthy to the experiment performed.
It should include typed sample calculations for the results. Photos of hand-written calculations are NOT ACCEPTABLE.

It should include the discussion questions for each experiment. The answers are required but do not add the actual discussion questions. Answer all parts of the questions in complete sentences and paragraph form. NO bulleting or numbering is acceptable.GENERAL
CHEMISTRY
1111
LAB MANUAL
Student Version
Florida Institute of Technology | 502OPS – 150 W University Bl vd, Melbourne, FL 32901
Table of Contents
Reference Materials __________________________________________________ III
Plagiarism Handout _______________________________________________________ IV
How to Keep a Hand-written Lab Notebook ________________________________________VIII
How to Keep an Electronic Lab Notebook_________________________________________ X
Lab Notebook Rubrics ____________________________________________________ XIV
How to Write a Lab Report _______________________________________________ XVI
General Lab Report Rubric ____________________________________________ XIV
Lab Policies and Safety _____________________________________________ XVI
Experiment 1: Determining the Density of Metals and Liquids _______________ 17
Determining Density Introduction ___________________________________________ 18
Determining Density Safety ______________________________________________________ 20
Determining Density Experimental Procedures ___________________________________ 21
Determining Density Data Sheet _____________________________________________ 23
Determining Density Report Requirements __________________________________ 25
Determining Density Report Rubric ______________________________________ 27
Experiment 2: Alka Seltzer Stoichiometry _______________________________ 30
Alka Seltzer Stoichiometry Introduction ______________________________________ 31
Alka Seltzer Stoichiometry Safety ________________________________________________ 32
Alka Seltzer Stoichiometry Experimental Procedures ______________________________ 33
Alka Seltzer Stoichiometry Data Sheet ________________________________________ 34
Alka Seltzer Stoichiometry Report Requirements _____________________________ 35
Alka Seltzer Stoichiometry Report Rubric _________________________________ 36
Alka Seltzer Stoichiometry Calculations ________________________________ 38
Experiment 3: Exploring the Properties of Gases _________________________ 39
Properties of Gases Introduction ____________________________________________ 40
Properties of Gases Safety ______________________________________________________ 41
Properties of Gases Experimental Procedures ___________________________________ 42
Part I. Pressure and Volume ___________________________________________________ 42
Properties of Gases Data Sheet ______________________________________________ 46
Properties of Gases Report Requirements ___________________________________ 47
Properties of Gases Report Rubric _______________________________________ 48
Experiment 4: Beer’s Law _____________________________________________ 51
Beer’s Law Introduction ___________________________________________________ 52
I
Beer’s Law Safety ______________________________________________________________ 54
Beer’s Law Experimental Procedures ___________________________________________ 55
Beer’s Law Data Sheet _____________________________________________________ 58
Beer’s Law Report Requirements __________________________________________ 59
Beer’s Law Report Rubric ______________________________________________ 60
Beer’s Law Calculations _____________________________________________ 63
Experiment 5: Determining the Enthalpy of a Chemical Reaction ____________ 64
Determining Enthalpy Introduction __________________________________________ 65
Determining Enthalpy Safety ____________________________________________________ 72
Determining Enthalpy Experimental Procedures __________________________________ 73
Determining Enthalpy Data Sheet ____________________________________________ 79
Determining Enthalpy Report Requirements _________________________________ 86
Determining Enthalpy Report Rubric _____________________________________ 87
Determining Enthalpy Calculations ____________________________________ 89
Experiment 6: Cycle of Copper ________________________________________ 93
Cycle of Copper Introduction _______________________________________________ 94
Cycle of Copper Safety _________________________________________________________ 97
Cycle of Copper Experimental Procedures _______________________________________ 98
Cycle of Copper Data Sheet ________________________________________________ 102
Cycle of Copper Report Requirements _____________________________________ 104
Cycle of Copper Report Rubric _________________________________________ 105
Experiment 7: Chemical Bonding _____________________________________ 108
Chemical Bonding Introduction ____________________________________________ 109
Chemical Bonding Experimental Procedures ____________________________________ 111
Chemical Bonding Data Sheet ______________________________________________ 113
Chemical Bonding Report Requirements ___________________________________ 115
II
Reference Materials
Reference
Materials
III
Plagiarism Handout
Why is plagiarism a big deal? You may have heard many justifications for plagiarism. It’s
not as if you are stealing money from a website by copying their text – the site is available
for free. Your friend permitted you to copy his lab report that he wrote last year. You and
your lab partner experimented together, so you should write the same report.
The problem:
Your lab instructor is grading your lab report to see how well you, and only you,
understand the experiment you performed. Copying a report doesn’t demonstrate that
you know the material. It just shows that you can press CTRL-C and CTRL-V. If you don’t
write your own report and know that you must write your own report, you are being
dishonest. Therefore, you get a zero for your grade, and the lab coordinator will report
your actions to the Dean of Students.
Your instructors in high school and college see more plagiarized assignments by students
because computers and the internet make information so much easier to store, distribute
and copy. Technology is also making it easier for your teachers to detect plagiarism. The
General Chemistry lab program stresses plagiarism because we want you to know that
we think this is a serious problem, and we want you to avoid it.
The Solution:
Understand what plagiarism is and how to avoid it. If you are unsure if you might be
committing plagiarism, ask for help! Contact the General Chemistry Coordinator or your
GSA before turning in your report, and they will provide you with guidance.
There are some things that we do allow and encourage you to do. You may work with a
lab partner or another student when writing your report, as long as you write your own
report – in your own words. You may get help writing from a tutor or your lab instructor.
You can copy graphs and blank tables to organize your experiment data provided to
you on Canvas.
Below are some examples of common ways students plagiarize their General Chemistry
lab reports. These definitions of plagiarism regularly appear in lab reports and derive from
plagiarism
rules
found
in
Florida
Tech’s
Student
Handbook
(http://assets.fit.edu/scripts/policy_view.php?id=2490) and other online resources can
IV
provide a thorough explanation (e.g., http://plagiarism.org/plagiarism-101/types-ofplagiarism/).
1. Cut and paste from another student’s report
The original report may belong to a student in another class, a student who took General
Chemistry in a previous semester, or maybe the student is your lab partner. It doesn’t
matter; you cannot do this for any reason. This is plagiarism. Suppose you don’t have
time to write your report, turn it in late for partial credit. If you have trouble writing clearly,
get help from the Academic Support Center, your lab instructor, or a tutor. There is no
excuse for copying another student’s lab report.
2. Reuse the lab report that you wrote when you took this class
previously
Reusing a report that you wrote previously is just like copying another report, except that
you were the original report’s author. It doesn’t matter. This is plagiarism. Since this is
a new semester, we expect your work to be new as well. Your reports should be your own
original work, not copies of work you did last semester.
3. Copy text from another source
Another source of text could be a website or the lab handout itself. Copying text from
another source is wrong, just like copying another student’s lab report is wrong. Students
sometimes copy the procedure directly from the lab handout. They have explained that
since they followed the procedure exactly as written in the handout, they should write their
procedure precisely as provided. No. This is plagiarism.
4. Quote extensive amounts of text
Do not copy and paste sentences into your report, then put quotes around them. Quoting
another source in a lab report shows that the student does this because they know the
quote contains the correct information, but the student is either too lazy or does not
understand what the quote means. This is plagiarism. Here is an example with the
copied and quoted text highlighted:
Lightning is a spectacular event. Lightning bolts are described as “a common
phenomenon—about 100 strike Earth’s surface every single second—yet their power is
V
extraordinary. Each bolt can contain up to one billion volts of electricity. This enormous
electrical discharge is caused by an imbalance between positive and negative charges.
During a storm, colliding particles of rain, ice, or snow increase this imbalance and often
negatively charge the lower reaches of storm clouds. Objects on the ground, like steeples,
trees, and the Earth itself, become positively charged—creating an imbalance that nature
seeks to remedy by passing current between the two charges.” 1In this experiment, we
used a Tesla coil to simulate the chemical reactions that occur in lightning bolts to
generate NO2 gas.
References:
1. Lightning,
National
Geographic
website,
http://environment.nationalgeographic.com/
environment/natural-disasters/lightning-profile/, accessed on October 1, 2011.
The quote is accurate, and the student cited it at the end of the report. Regardless, this
is plagiarism. The student did not write most of the background section – most of it was
copied from another source. Under some circumstances, providing a quote within a report
could be legitimate. For instance, if you discuss a quote by a famous person, you could
provide that quote. This exception is not relevant to general chemistry lab reports, so do
not copy text and put quotes around it. Write all the text yourself.
5. Copy text from another source, then change some words
Don’t copy text and then change a few words in each sentence. This is plagiarism.
Students might do this for their procedures or background sections. Compare the text on
the left is the original, and the text on the right is slightly modified. All text on the right that
is the same as the text on the left is highlighted.
1. Cut a length of pure copper wire that A length of pure copper wire that weighs
weighs about 0.25 g (about a 5-cm length about 0.25 g is cut. Since it was not bright
of 20-gauge copper wire).
and shiny, it was cleaned with steel wool,
2. If it is not bright and shiny, clean it with rinsed with water, and dried with a tissue.
steel wool, rinse it with water, and dry it It was weighed, and the exact mass was
with a tissue.
recorded on the datasheet. The wire was
VI
3. Weigh it and record the exact mass on coiled into a flat spiral and placed in the
your datasheet.
bottom of a 250-mL beaker.
4. Coil the wire into a flat spiral and place
it in the bottom of a 250-mL beaker.
Not only are many of the phrases the same, but the structure of each sentence is also
identical, with only the verb tense changed (e.g., “record the exact mass” changed to “the
exact mass was recorded”). It looks different because the list is now a paragraph, but the
wording is still too similar. Do not do this.
Below is another example of the same procedure but written to be entirely different and
original.
*A piece of copper wire was cleaned with steel wool then rinsed and dried. It was weighed,
then rolled up, and put into a 250 mL beaker. *
*This is the same procedure with all necessary details provided. It is just a different way
of writing the procedure. While a few phrases are the same, it is evident that the writing
is original.
VII
How to Keep a Hand-written Lab Notebook
The expectations of a lab notebook are that any novice researcher can refer to this
document and perform the experiment exactly the way the writer of the notebook had
done. The results from the lab notebook should be reproducible and easy to follow. These
are not meant to be publishable documents; therefore, they do not need to be perfect.
The most important details about a lab notebook are that every detail of the experiment
must be recorded in the book. If the researcher had to change the procedure in any way,
those changes must be documented for the next person to reproduce. All data found must
be recorded in it. Calculations or explanations to comprehend the results must be
documented as well. Below is an example of a lab notebook.
Every lab notebook should include the following:
1. Table of Contents
2. Numbered pages
3. Journal entries for each lab performed; Must include the following information:
a. Lab Title
b. Date Lab was performed
c. Objectives of the lab
d. Condensed Procedure
e. Data tables that reflect the data sheet: Must include graphs
f. Calculations and Conclusions
g. Discussion questions
Example Notebook:
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IX
How to Keep an Electronic Lab Notebook
Journal entries for each Lab performed; must include the following information:
a. Lab Title
b. Your Name
c. Your Lab Partner’s Name
d. The date the Lab is performed
e. Objectives of the Lab
f. Condensed Procedure
g. Data tables that reflect the datasheet: Must include graphs
h. Calculations and Conclusions
i.
Discussion questions
Navigating Benchling
1. Refresh the browser. In the All Projects drop-down menu, change to the General
Chemistry project:
X
2. Start by creating a new project:
3. Next, select Project and fill in the criteria with your information:
4. The location will be your name. You can then create an entry by clicking the +
sign on the left side of the page, select entry, then blank entry:
XI
Example Notebook Entry:
XII
All the criteria listed above must be filled in entirely and in prose (complete sentences) to
receive credit on this portion of your lab grade. The following preliminary information
must be filled out before showing up to Lab to receive FULL CREDIT for the lab
notebook: Title, Objectives, Procedure, Blank Data Table, and Discussion
Questions. If you have any further questions regarding this protocol with the notebooks,
please contact your GSA immediately.
NOTE: If you arrive late to Lab, you will receive a 50% Late Penalty on the Lab Notebook
assignment for the experiment to which you are late.
XIII
Lab Notebook Rubrics
Every student will be required to keep an electronic notebook online through Benchling.
The data in this notebook will be accessible by the student, their respective GSA, the
Lead GSA, and the course instructor for grading. The lab notebook is primarily for the
student to track their data and results throughout the Lab. Lab notebooks grades
principally depend on COMPLETION. IF the student feels this is unfair or has any further
questions, please contact your GSA or course instructor.
Pre-lab notebooks are due at 11:59 pm the day before the Lab meets to perform
the experiment. Post-Lab notebooks are due at 11:59 pm a week after the Lab
performs the experiment.
Pre-Lab Notebook
Objectives
5 pts: A brief
explanation of what
the student will learn
from this Lab. What
question will this
experiment answer?
Procedures
5 pts: Discussion
5 pts: Full credit
requires condensed
procedures from the
lab manual written in
your own words.
2.5 pts: The student
2.5 pts: Procedures
tried, but the objective
not complete or
does not hit the mark.
cannot be followed.
0 pts: None included,
not completed on
time, or plagiarized.
Discussion Questions
0 pts: None
included, not
completed on time, or
questions pulled directly
from the lab manual.
Plagiarized questions are
to ensure students have
seen the questions.
2.5 pts: Some questions
included but not all.
0 pts: None included, not
completed on time, or
plagiarized.
plagiarized.
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Post-Lab Notebook
Pre-Lab
Alterations
5 pts: Student fixed
any problems from
the pre-lab
notebook.
Data & Results
Sample Calculations
5 pts: All data tables
5 pts: All required
filled in. Graphs and
sample calculations
figures included.
included.
2.5 pts: Some but not
2.5 pts: Fixed some 2.5 pts: Some but not all
errors but not all.
data and results included.
0 pts: No errors
0 pts: Tables not filled in
fixed, not completed and figures not included,
all calculations
included.
0 pts: No calculations
included, not
on time, or
or not completed on time, completed on time, or
plagiarized.
or plagiarized.
plagiarized.
XV
How to Write a Lab Report
The form of this report is a brief technical report. It should be no more than four pages,
double spaced, and justified text. You are expected to report the data in tables and graphs
with a brief interpretation of your results. You MUST answer all discussion questions in
complete sentences and paragraph form.
ALL Lab Reports will be uploaded to Canvas and scored through Turnit-In.
Accepted file formats:
Unaccepted file formats:
1) .pdf
1) .odt
2) .docx
2) .rtf
3) .txt
4) .pptx
5) xlsx
Lab reports are due at 11:59 pm one week after the Lab performs the experiment.
GSAs will accept late Lab reports for one week after the due date for 50% credit.
Items expected in your report:
1. A header must be included with your name, your lab partner’s name, the date the
experiment was performed, and a lab title.
2. It should give a brief description of the importance of the experiment and
procedures. Essentially this is an objective. What was the point of the experiment?
3. It should include any changes to the procedure not included in the lab notebook.
Otherwise, students must write “Procedures followed as written in the lab
notebook.”
4. It should include any tables and graphs (appropriately labeled) and a one-sentence
description of what the figure is showing.
5. It should include a brief analysis of the results. The analysis should describe any
trends exhibited in the data, what the data shows/indicates/proves, and anything
you find noteworthy to the experiment performed.
6. It should include typed sample calculations for the results. Photos of hand-written
calculations are NOT ACCEPTABLE.
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7. It should include the discussion questions for each experiment. The answers are
required but do not add the actual discussion questions. Answer all parts of the
questions in complete sentences and paragraph form. NO bulleting or numbering
is acceptable.
Formatting expected in your report:
a. The header should be on the top left corner of the first page of the report.
b. All tables must be labeled ABOVE the table. Under each table, provide a onesentence description of what the table is showing the reader.
c. Any figure or graph must be labeled UNDER the figure or graph. Following the
figure/graph label, provide a one-sentence description of what it is showing the
reader.
d. Analysis should be a separately labeled section.
e. You must use either 12-point Times New Roman font or 11-point Arial font.
f. You must double-space.
g. The text of the report must be justified.
h. Standard 1-inch margins.
i.
Must be writing in the third person (i.e., no I, you, we, etc.) and past tense.
j.
Everything must be typed in complete sentences and paragraph form. Bulleting or
numbering is NOT ACCEPTABLE.
Failure to adhere to any of the above guidelines will result in points deducted from the
assignment. Failure to turn the assignment in on-time will result in a 50% points reduction.
If you have questions regarding these guidelines or Lab report expectations, contact your
GSA or the Lead GSA.
XIII
General Lab Report Rubric
Section
Formatting
3 points
Prose
1 point
Grammar
1 point
Criteria
Follows report
guidelines
(justified text,
double-spaced,
1-inch margins,
single
font/color/size).
Header
2 points
Objectives
2 points
The objective is
a brief
description of
the purpose of
the experiment.
Data &
Results
The student
followed all
formatting
guidelines.
The report is
written in prose
or paragraph
The report was
form (i.e., no
written entirely
bulleted lists and in prose.
no numbered
lists).
No more than 5
Correct English
typos or
grammar,
grammatical
spelling, and use
errors. The
of the third
student uses
person (i.e., no I,
the third
you, we, etc.)
person.
Follows header
guidelines
(student name,
lab partner(s)
name, date the
experiment was
performed, lab
title).
Procedures
1 point
Full Credit
All header
guidelines
were followed.
The student
understands
what the
experiment
was about and
why they did it.
Includes
Writes
standard entry
procedures were
unless
followed as
significant
written in the lab
changes were
notebook.
made.
Types up all of
Tables are
the tables and
appropriately
Half Credit
No Credit
The student
did not follow
one or two
formatting
guidelines.
The student
did not follow
formatting
guidelines.
The student
did not follow
three or more
formatting
guidelines.
The report
contains some
prose and
some lists.
No prose or
paragraphs.
No more than
10 typos or
grammatical
Barely
errors. Some
readable.
use of personal
pronouns.
The students
did not follow
one or two
header
guidelines
were not
followed.
The student
did not follow
header
guidelines.
The student
did not follow
three or more
header
guidelines.
The student
does not quite
show
understanding
of the
experiment.
No objective
included. The
objective does
not make
sense.
The student
includes
insignificant
changes.
Data doesn’t
match the Lab
Includes a
detailed
procedure or
does not
include this
section at all.
A picture or
image of the
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7 points
data collected in
the Lab.
Includes figures.
This section
includes typed
Calculations
examples of all
5 points
designated
calculations.
Analysis
8 points
Brief but
thorough
explanation of
results, trends,
and what they
mean.
Discussion
Questions
20 points
Experiment
dependent
questions
answered.
labeled (each
correctly
identified,
appropriate
title, and units
are included),
and data is
complete.
Required
figures are also
included.
Includes a
typed example
of all
calculations
performed.
Units are
included.
Includes a
separately
labeled section
with an
explanation of
results, trends,
and what they
mean.
Questions
answered
correctly and
using complete
sentences.
notebook;
tables are
presented
incorrectly or
not
properly
labeled, data
makes no
sense,
etc.
Some
calculations
are missing,
OR units are
missing.
data sheet or
notes taken is
given as data
results (i.e.,
screenshots of
the Benchling
lab notebook).
You are
missing most
or all data and
results.
A picture or
image of the
data
sheet or notes
taken is given
as calculations
OR none
included.
Some trends
are explained
or missing or
inadequate
explanation.
No analysis
included. The
student writes
procedure as
analysis.
Question
dependent
incomplete
response.
No answer
included, or
answer does
not make
sense.
XV
Lab Policies and Safety
Violation
Penalty
Not wearing goggles when directed.
Not wearing gloves when directed.
Not wearing lab coat during experiments
or unbuttoned lab coats.
Not wearing long pants or a long skirt that
completely cover your legs.
Not wearing a face covering over both
your nose and mouth.
Not wearing shoes that completely cover
your feet.
Refusing to tie back long hair.
Eating or drinking in the Lab. Including
chewing gum!
Food or drink at the student’s lab
workspace.
Behaving inappropriately (at the
discretion of any GSA or Florida Tech
Staff member).
1) Warning.
2) Earn 50% off your lab notebook.
3) The student gets dismissed from
Lab immediately and receives a
zero on that day’s assignments
with no opportunity to make up the
work.
*For safety reasons, GSAs and course
instructors may skip to third offense
penalty at their discretion.
Show up to Lab unprepared: forgot
goggles, lab coat, appropriate
shoes/attire, etc.
Receive 50% off your lab notebook. You
will have 5 mins after the start of the Lab
to obtain your materials. Failure to obtain
materials results in a zero for that day’s
assignments with no opportunity to make
up the work.
Failure to complete the pre-lab quiz AND
pre-lab notebook before attending Lab.
Dismissed from Lab and receive a zero on
that day’s assignments with no opportunity
to make up the work.
Have food or drink in the Lab away from
your workspace but still in the lab room,
including closed containers in your
backpack.
Receive 50% off your lab notebook.
Arrive late within the 5-minute window.
Receive 50% off your lab notebook.
Arrive late after the 5-minute window.
Dismissed from Lab and receive a zero on
that day’s assignments with no opportunity
to make up the work.
XVI
Experiment 1: Determining the Density of Metals and Liquids
Experiment 1:
Determining
Density
17
Determining Density Introduction
Materials can be distinguished from one another because they have different physical
and chemical properties. A property that is often used to identify materials is density.
Density is defined as the amount of matter in a given space, which correlates to the ratio
of a material’s mass to its volume.
=

The mass is the amount of matter in a material or object, usually given in grams
(g) or kilograms (kg). Whereas volume is the amount of space the object occupies usually
given in terms of milliliters (mL), liters (L), or cubic centimeters (cm3). In this experiment,
you will measure the mass and volume of six unknown metal samples. The metal samples
may vary in mass, size, or shape. In Part 1 of this experiment, you will calculate the
volume of the samples by measuring the length, width, height, and/or diameter of the
object (depending on its shape) using a digital caliper. Table 1 provides volume equations
for a selected group of shapes. Some of the metal objects are not perfect examples of
any of the shapes. You must choose which shape they most closely resemble and use
the corresponding formula for volume.
Table 1: Volume Equations for 3D Shapes
Shape
Equation
Shape
Equation
sphere
V = 4/3 π r3
pyramid
V = (L x W x H) / 3
rectangular prism
V=LxWxH
prolate ellipsoid
V = 4/3 π r2 (L/2)
right circular cylinder
V = π r2 H
right circular cone
V = π r2 (H/3)
NOTE: A straight line from the center measures the radius of a circle. A prolate ellipsoid
is an elongated spheroid 3-dimensional shape.
In Part 2, you will determine the volume of the samples by water volume displacement
using a graduated cylinder. The data obtained in both parts will be used to calculate the
densities of the unknown metal samples. From the density, you will identify the
composition of the metal samples by comparing them to the theoretical densities of the
metals presented in Table 2.
18
Table 2: Density of Selected Metals
Metal
Density (g/cm3)
Metal
Density (g/cm3)
Mg
1.74
Brass
8.53
Al
2.70
Pb
11.34
Ti
4.51
Cu
8.96
Ag
10.5
Ni
8.90
Zn
7.14
Mn
7.3
Sn
7.26
Au
19.3
Steel
7.86
Zr
6.52
In Part 3, you will explore the power of density and determine the density of six solutions.
You will create six separate solutions of increasing amounts of salt with a consistent
amount of DI water. By increasing the amount of salt in the solution but keeping the
amount of water constant, you prepare solutions that have increasing densities. The more
salt that is mixed into a measured amount of water, the higher the density of the
solution. The density straw shows a solution with a low density stacks on top of a solution
with a higher density.
You might expect the solutions to just fall out of the straw as you lift the straw from a
solution. However, the invisible forces acting on the liquid inside the straw are
manipulated by holding your finger to block the top opening of the straw. You create a
pressure seal with your finger causing the external air pressure (the upward force) to
become stronger than gravity (the downward force) acting on the liquid. As the capped
straw is removed from the liquid gravity tugs the solutions downward, which creates a
slight vacuum in the empty part of the straw. That lowers the air pressure inside the straw,
which is why you need your thumb to cap the straw. This prevents air pressure from
equalizing in the straw. If you remove your thumb, the air pressure equalizes, and gravity
simply moves the colored solutions out.
19
Determining Density Safety
Always wear proper personal protective equipment (i.e., your goggles and lab coat).
Always wear proper attire: long pants/skirt with no holes, shoes that completely cover
your feet, and keep long hair tied back.
Gloves must be worn while handling chemicals. However, gloves must not be worn in the
hallways or when interacting with non-chemical entities (e.g., door handles, eyes, or
laptops/cell phones). Remove gloves before exiting the lab unless transporting chemicals
with the aid of an ungloved partner to open doors.
Place your backpacks, skateboards, etc., on the counter in the back of the lab. It is
important that people don’t trip and fall when working around hazardous chemicals. You
may not wear headphones in the lab because they distract you from your environment
creating a hazardous lab space.
Waste Disposal
Dispose of all waste in the non-regulated waste container labeled NR.
Disposable face masks can be thrown in the regular trash.
20
Determining Density Experimental Procedures
Part 1: Determine Density by Mass and Dimensions
1. You were given a bag with 6 unknown metal samples. Record the Bag ID on your
data sheet and in your lab notebook.
2. Identify the shape of each metal sample and list ALL physical properties of the
sample on your data sheet (i.e., shiny, smooth, color, texture, etc.). • Note – You
will compare the density from Part 1 to Part 2. Be sure you can quickly identify
metals 1-6 based on their physical properties. Record measurements for the same
metal in both tables on the Data Sheet and in your lab notebook (i.e., data for Metal
1 in Table 1 should be the same as the data for Metal 1 in Table 2).
3. Weigh each metal and record the mass on your data sheet and in your lab
notebook. Significant figures are essential.
4. Take the necessary measurements of length, width, height, and diameter
(depending on the shape) using the digital caliper. Record the measurements in
your lab notebook. Significant figures are essential.
5. Calculate the volume of each metal sample (reference Table 1 in the procedure).
Record the volume in your lab notebook. NOTE: Not all boxes on the lab notebook
will have a value. (e.g., A rectangular prism does NOT have a diameter).
Significant figures are essential.
6. Calculate the density of each metal sample. Record the density in your lab
notebook. Significant figures are essential.
Part 2: Determine Density by Mass and Water Volume Displacement
1. Based on your volume measurements in Part 1 and the size of your metals, choose
the appropriate graduated cylinder to measure the water-volume displacement of
each metal (50 mL or 10 mL). Choosing the correct glassware will result in more
accurate results. Your metal sample should fit into the chosen graduated cylinder
EASILY. The metal should not get stuck inside the graduated cylinder.
2. For each sample, fill the graduated cylinder with enough tap water so that, once
added, the metal sample will be completely submerged in the water without going
higher than the upper-most increment. Record the exact volume of the water in the
21
graduated cylinder in your lab notebook. Significant figures are essential. • For
example, if your volume for a given metal was 5.0 g/mL in Part 1, you may want to
try adding 7 mL of tap water in your graduated cylinder to start.
3. Tilt the graduated cylinder as far as possible (without spilling any water) and VERY
CAREFULLY SLIDE in the metal sample to the bottom of the graduated cylinder
without breaking the glass or splashing any water out. Record the volume of the
water with the metal in your lab notebook. Significant figures are essential.
4. Calculate and record the volume of each metal in your lab notebook. Significant
figures are essential.
5. Calculate and record the density of each metal in your lab notebook. Significant
figures are essential.
Part 3: Liquid Layers – Salt Water Density Straw
1. Clean 5 test tubes and label them.
2. Measure 0.50 gram (g) of salt and place it into test tube one.
3. Repeat step 2, increasing the amount of salt by 0.50 grams for each test tube (i.e.,
1.00 g for test tube #2, 1.50 g for test tube #3, etc.)
4. To each test tube, add 12 mL of warm DI water.
5. Stir each salt and water solution with your glass stir rod until all of the salt has been
dissolved.
6. Use food coloring to dye the solutions in each test tube. Add 3-4 drops of red to
test tube #1, 1 drop of red and 2 drops of yellow to test tube #2, 3 drops of yellow to
test tube #3, 0.5-1 drop of green to test tube #4, 0.5-1 drop of blue to test tube #5.
7. Obtain a clear drinking straw. Keeping both ends open, dunk the bottom end of the
straw about 0.5 inches into the liquid of test tube #1. Cap the top of the straw firmly
with your thumb and remove the straw from the solution.
8. Now that you have the first solution in the straw, dip the end of the straw into test
tube #2. This time dip the straw about 0.5 inches deeper than you did into the first
solution. After you’ve dipped the straw, lift your thumb and replace it.
9. Continue the dipping process until you have all six colored solutions inside
the straw. It’s a density column of saltwater!
10. Dispose of all waste in the waste container labeled non-regulated (NR) waste.
22
Determining Density Data Sheet
Name_______________________________________________________________
Section___________________
Metal
Date_____________________
List ALL
Mass
Length
Width
Height
Diameter
Volume of Object
Density
Physical Properties
(g)
(cm)
(cm)
(cm)
(cm)
(cm3)
(g/cm3)
Shape:_______________
1
Shape:_______________
2
Shape:_______________
3
Shape:_______________
4
Shape:_______________
5
Shape:_______________
6
23
Did you use a
Mass (g)
Metal
(from Table 1)
50.0 or 10.0 mL
Volume of
graduate
water (mL)
cylinder?
Volume of
water + metal
(mL)
Density
Volume of
metal (mL)
Density (g/mL)
(g/cm3)
From Table 1
1
2
3
4
5
6
Identify each of your Metal samples:
Metal 1: ______________________ Metal 2: ______________________ Metal 3: ______________________
Metal 4: ______________________ Metal 5: ______________________ Metal 6: ______________________
24
Density
Test Tube
Salt (g)
DI (mL)
(g/mL)
1
2
3
4
5
25
Determining Density Report Requirements
Standard Report Requirements
Each student will write a short report for this experiment. Write everything in your own
words. Do not copy or rephrase what somebody else writes. Type the report using
justified alignment, double spacing, 1-inch margins, and Times New Roman 12-point font
or Arial 11-point font. It should include the following sections:
Header, objectives, procedures, data and results, analysis, calculations, and discussion.
Experiment Specific Requirements
Be sure you have shown ALL calculations on your lab notebook to receive full credit.
Use Table 2 of the procedure and your calculated densities to identify the composition of
your six metal samples. Record your results on the lab notebook.
Discussion Questions
Copy these questions into the lab notebook for perusal during the lab. Answer these
questions in prose (complete sentences, paragraph form) in the lab report.
1. Which method of measurement would be more accurate to calculate the density
of an object? Caliper/balance or volume based on the displacement of water?
Why? What about irregularly shaped objects? (5 pts)
2. What is the definition of an alloy? Which metal(s) measured is (are) an alloy metal
material. (HINT refer to Table 2 for possible alloys) (5 pts)
3. Sam needs 20 g of hydrochloric acid (HCl). The density of hydrochloric acid is
1.164 g/mL. Find the volume of hydrochloric acid they need. (5 pts)
4. A metal bar has a density of 15.9 g/mL what is the density in kg/L? (Show work for
full credit) (5 pts)
26
Determining Density Report Rubric
Section
Formatting
3 points
Prose
1 point
Grammar
1 point
Header
2 points
Objectives
2 points
Procedures
1 point
Criteria
Full Credit
Half Credit
No Credit
Follows report
guidelines
(justified text,
double-spaced,
1-inch margins,
single
font/color/size).
The student
followed all
formatting
guidelines.
The student did
not follow one
or two
formatting
guidelines.
The student
did not follow
formatting
guidelines.
The student
did not follow
three or more
formatting
guidelines.
The report is
written in prose or
paragraph form
(i.e., no bulleted
lists and no
numbered lists).
The report
was written
entirely in
prose.
The report
contains some
prose and
some lists.
No prose or
paragraphs.
Correct English
grammar,
spelling, and use
of the third
person (i.e., no I,
you, we, etc.)
No more than
5 typos or
grammatical
errors. The
student uses
the third
person.
No more than
10 typos or
grammatical
errors. Some
use of personal
pronouns.
Barely
readable.
The students
did not follow
one or two
header
guidelines were
not followed.
The student
did not follow
header
guidelines.
The student
did not follow
three or more
header
guidelines.
The student
does not quite
show
understanding
of the
experiment.
No objective
included. The
objective
does not
make sense.
The student
includes
insignificant
changes.
Includes a
detailed
procedure or
does not
include this
section at all.
Follows header
guidelines
(student name,
lab partner(s)
name, date the
experiment was
performed, lab
title).
The objective is a
brief description
of the purpose of
the experiment.
Writes
procedures were
followed as
written in the lab
notebook.
All header
guidelines
were followed.
The student
understands
what the
experiment
was about and
why they did
it.
Includes
standard entry
unless
significant
changes were
made.
27
Data &
Results
7 points
Types up all of
the tables and
data collected in
the Lab. Includes
figures.
This section
Calculations includes typed
5 points
Analysis
8 points
Discussion
Question 1
5 points
examples of all
designated
calculations.
Tables are
appropriately
labeled (each
correctly
identified,
appropriate
title, and units
are included),
and data is
complete.
Required
figures are
also included.
Data doesn’t
match the Lab
notebook;
tables are
presented
incorrectly or
not
properly
labeled, data
makes no
sense,
etc.
Includes a
typed example
of all
calculations
performed.
Units are
included.
Some
calculations are
missing, OR
units are
missing.
Includes a
separately
Brief but thorough labeled
explanation of
section with
results, trends,
an explanation
and what they
of results,
mean.
trends, and
what they
mean.
Which method of
measurement
would be more
accurate to
calculate the
density of an
Explains
object?
which method
Caliper/balance
is better and
or volume based
why.
on the
displacement of
water? Why?
What about
irregularly shaped
objects?
A picture or
image of the
data sheet or
notes taken is
given as data
results (i.e.,
screenshots
of the
Benchling lab
notebook).
You are
missing most
or all data
and results.
A picture or
image of the
data
sheet or
notes taken is
given as
calculations
OR none
included.
Some trends
are explained
or missing or
inadequate
explanation.
No analysis
included. The
student writes
procedure as
analysis.
Explains the
correct
methods for the
shapes but
does not
explain why.
No answer
included, or
answer does
not make
sense.
28
Discussion
Question 2
5 points
Discussion
Question 3
5 points
Discussion
Question 4
5 points
What is the
definition of an
alloy? Which
metal(s)
measured is (are)
an alloy metal
material.
Sam needs 20 g
of hydrochloric
acid (HCl). The
density of
hydrochloric acid
is 1.164 g/mL.
Find the volume
of hydrochloric
acid they need.
A metal bar has a
density of
15.9g/mL what is
the density in
kg/L?
Does not state
definition of an
Gives the
alloy but states
definition of an what metals
alloy and
were alloys. OR
states which
states definition
metals were
of an alloy but
alloys.
does not state
which metals
were alloys.
No answer
included, or
answer does
not make
sense.
Shows
complete
calculation.
States answer
but does not
show work.
No answer
included, or
answer does
not make
sense.
States answer
but does not
show work.
No answer
included, or
answer does
not make
sense.
Shows
complete
calculation.
29
Experiment 2: Alka Seltzer Stoichiometry
Experiment 2:
Alka Seltzer
Stoichiometry
30
Alka Seltzer Stoichiometry Introduction
Stoichiometric measurements are among the most important in chemistry, they
indicate the proportions by mass in which various substances react. Stoichiometry
includes writing and balancing chemical equations, stoichiometric coefficients, molar
ratios of reactants and products, limiting reagents, theoretical yields and percent yields.
Alka-Seltzer is an over the counter antacid and pain relief medication which is
taken by dissolving it in water before ingesting. This drug contains aspirin (acetylsalicylic
acid), citric acid, and sodium bicarbonate (NaHCO3). Immediately after the tablet is
placed in water, an acid-base reaction involving sodium bicarbonate takes place which
leads to the generation of carbon dioxide through bubbling.
HCO3- (aq) + H+ (aq) → H2O (l) + CO2 (g)
The release of carbon dioxide results in a net weight loss after the reaction. With the
weight loss, one should be able to calculate the amount of sodium bicarbonate that
reacted and determine the percent by mass of NaHCO3 contained in Alka-Seltzer tablets.
31
Alka Seltzer Stoichiometry Safety
Always wear proper personal protective equipment (i.e., your goggles and lab coat).
Always wear proper attire: long pants/skirt with no holes, shoes that completely cover
your feet, and keep long hair tied back.
Gloves must be worn while handling chemicals. However, gloves must not be worn in the
hallways or when interacting with non-chemical entities (e.g., door handles, eyes, or
laptops/cell phones). Remove gloves before exiting the lab unless transporting chemicals
with the aid of an ungloved partner to open doors.
Place your backpacks, skateboards, etc. on the counter in the back of the lab. It is
important that people don’t trip and fall when working around hazardous chemicals. You
may not wear headphones in the lab because they distract you from your environment
created a hazardous lab space.
Waste Disposal
Dispose of all waste in the non-regulated waste container labeled NR.
Disposable face masks can be thrown in the regular trash.
32
Alka Seltzer Stoichiometry Experimental Procedures
1. Measure 60 mL of deionized water using a graduated cylinder. Pour into a 250 mL
beaker.
2. In the balance room, weigh and record the total weight of the beaker and water
using an electronic balance.
3. In the balance room, weigh and record the weight of an Alka-Seltzer tablet using
a weigh boat.
4. After returning to the lab, drop the tablet into the beaker, carefully swirl the beaker
to ensure complete dissolution of the tablet.
5. In the balance room, weigh and record the weight of the beaker and all the contents
when the bubbling ceases. Refer to the data sheet and copy into your lab
notebook.
6. After returning to the lab, wash and rinse the beaker with water.
7. Calculate the mass of the carbon dioxide generated.
8. Calculate the mass of NaHCO3 reacted.
9. Calculate the percent by mass of the reacted NaHCO3 in the tablet.
10. Repeat the experiment 5 times with the following vinegar and water amounts.
a. 10 mL of vinegar + 50 mL of water
b. 20 mL of vinegar + 40 mL of water
c. 30 mL of vinegar + 30 mL of water
d. 40 mL of vinegar + 20 mL of water
e. 50 mL of vinegar + 10 mL of water respectively.
Record values on the data sheet and in your lab notebook for each.
11. Plot the calculated percent by mass of the reacted NaHCO3 in the tablet versus
the volume of vinegar used using the Excel spreadsheet provided on Canvas.
12. Dispose of all waste in the waste container labeled Non-Regulated (NR) waste.
33
Alka Seltzer Stoichiometry Data Sheet
Name_______________________________________________________________
Section___________________
Date_____________________
Experiment #
Run 1
Run 2
Run 3
Run 4
Run 5
Run 6
Volume of vinegar
(mL)
0
10
20
30
40
50
Volume of water
(mL)
60
50
40
30
20
10
Weight of beaker and
liquid (g)
Weight of AlkaSeltzer tablet (g)
Weight of beaker
with liquid + weight
of tablet (g)
Weight of beaker
with all contents
after bubbling ceases
(g)
Weight loss (mass of
CO2)
Mass of NaHCO3
reacted
% by mass of the
NaHCO3 in a tablet
34
Alka Seltzer Stoichiometry Report Requirements
Standard Report Requirements
Each student will write a short report for this experiment. Write everything in your own
words. Do not copy or rephrase what somebody else writes. Type the report using
justified alignment, double spacing, 1-inch margins, and Times New Roman 12-point font
or Arial 11-point font. It should include the following sections:
Header, objectives, procedures, data and results, analysis, calculations, and discussion.
Experiment Specific Requirements
Show one sample calculation for how you calculated the mass of NaHCO 3 from the
amount of CO2 released.
Use Excel to plot the calculated percent by mass of the reacted NaHCO3 in the tablet
versus the volume of vinegar used. After the graph is complete, copy the graph into
your lab report and lab notebook. Do not make graphs by hand, and do not put
screenshots or pictures of your graph in your lab report. You must provide the graph
and data table in your report to receive full credit.
Discussion Questions
Copy these questions into the lab notebook for perusal during the lab. Answer these
questions in prose (complete sentences, paragraph form) in the lab report.
1. What is a limiting reactant? How does the graph change in correlation to the
limiting reactant? Which would you identify as the limiting reactant in trial 2 of this
experiment? Predict what might happen if the Alka-Seltzer tablet was dissolved
in 60 mL of vinegar. How will this affect the graph? (10 pts.)
2. What will be the effect on the reaction if HCl is used instead of vinegar? How will
the graph look? (5 pts.)
3. Balance the chemical equation below; (5 pts.)
CO32- (aq) + H+ (aq) →CO2 (g) + H2O (l)
35
Alka Seltzer Stoichiometry Report Rubric
Section
Criteria
Full Credit
Half Credit
No Credit
Formatting
3 points
Follows report
guidelines (justified
text, double-spaced,
1-inch margins,
single
font/color/size).
The student
followed all
formatting
guidelines.
The student did
not follow one
or two
formatting
guidelines.
The student
did not follow
formatting
guidelines. The
student did not
follow three or
more
formatting
guidelines.
Prose
1 point
The report is written
in prose or
paragraph form (i.e.,
no bulleted lists and
no numbered lists).
The report was
written entirely
in prose.
The report
contains some
prose and some
lists.
No prose or
paragraphs.
Grammar
1 point
Correct English
grammar, spelling,
and use of the third
person (i.e., no I,
you, we, etc.)
No more than 5
typos or
grammatical
errors. The
student uses
the third
person.
No more than
10 typos or
grammatical
errors. Some
use of personal
pronouns.
Barely
readable.
Header
2 points
Follows header
guidelines (student
name, lab partner(s)
name, date the
experiment was
performed, lab title).
All header
guidelines were
followed.
The students
did not follow
one or two
header
guidelines were
not followed.
The student
did not follow
header
guidelines. The
student did not
follow three or
more header
guidelines.
The student
does not quite
show
understanding
of the
experiment.
No objective
included. The
objective does
not make
sense.
Objectives
2 points
The objective is a
brief description of
the purpose of the
experiment.
Procedures
1 point
Writes procedures
were followed as
written in the lab
notebook.
Data &
Results
7 points
Types up all of the
tables and data
collected in the Lab.
Includes figures.
The student
understands
what the
experiment was
about and why
they did it.
Includes
standard entry
unless
significant
changes were
made.
Tables are
appropriately
labeled (each
correctly
identified,
appropriate
title, and units
are included),
and data is
complete.
The student
includes
insignificant
changes.
Data doesn’t
match the Lab
notebook.
Tables are
presented
incorrectly or
not adequately
labeled. Data
makes no
sense,
Includes a
detailed
procedure or
does not
include this
section at all.
A picture or
image of the
data sheet or
notes taken is
given as data
results (i.e.,
screenshots of
the Benchling
lab notebook).
You are
36
Required
figures are also
included.
Calculations
5 points
Analysis
8 points
Discussion
Question 1
10 points
Discussion
Question 2
5 points
Discussion
Question 3
5 points
etc.
missing most
or all data and
results.
A picture or
image of the
data
sheet or notes
taken is given
as calculations
OR none
included.
This section
includes typed
examples of all
designated
calculations.
Includes a
typed example
of all
calculations
performed.
Units are
included.
Some
calculations are
missing, OR
units are
missing.
Brief but thorough
explanation of
results, trends, and
what they
mean.
Includes a
separately
labeled section
with an
explanation of
results, trends,
and what they
mean.
Some trends
are explained or
missing or
inadequate
explanation.
No analysis
included. The
student writes
procedure as
analysis.
Defines limiting
reagent.
Calculates and
Only finishes
determines the
one of the parts
limiting reagent.
of the question.
Explains the
effect on the
graph.
No answer
included, or
answer does
not make
sense.
Explains both
questions.
Explains one
question or the
other but not
both.
No answer
included, or
answer does
not make
sense.
Gives the
correct
balanced
equation.
Not applicable
the answer is
either correct or
wrong.
No answer
included, or
answer does
not make
sense.
What is a limiting
reactant? How does
the graph change in
correlation to the
limiting reactant?
Which would you
identify as the
limiting reactant in
trial 2 of this
experiment? Predict
what might happen if
the Alka-Seltzer
tablet was dissolved
in 60 mL of vinegar.
How will this affect
the graph?
What will be the
effect on the
reaction if HCl is
used instead of
vinegar? How will
the graph look?
Balance the
chemical equation
37
Alka Seltzer Stoichiometry Calculations
The calculations performed in this lab can be as followed below. Please follow them as
written, and if you have any further questions ask you GSA.
According to the procedure, the data sheet asks you to solve for the mass of the reacted
CO2 from each tablet in the experiment after dissolving it with varying concentration of
acid and water solutions. Therefore, the first calculation investigates the weight of the
beaker with liquid + weight of the tablet:
ℎ ℎ + ℎ
3 + 4
= ℎ ℎ +
5 ℎ
The data table (line 6) then asks for the weight of beaker after the solution content ceases
bubbling. To do this, you must weigh the beaker after the experiment is complete,
meaning no more bubbling of the solution occurs (line 6). From this measurement, you
are then asked to find the weight loss (i.e. the mass of CO2) from CO2 gassing off:
2 = 5 − 6
7
Lastly, you need to find the mass of NaHCO3 reacted in the experiment (line 8). This can
be done by:
2 3

= 3
2
1
To accurately graph the percent by mass of the reacted NaHCO3 (line 9), you must then
convert the mass of NaHCO3 reacted into a percentage like so:
3
∗ 100 = % 3
ℎ ( 4)
38
Experiment 3: Exploring the Properties of Gases
Experiment 3:
Properties of
Gases
39
Properties of Gases Introduction
Objectives
During this experiment, you will:
i.
Conduct a set of experiments, each of which illustrates a gas law.
ii.
Gather data to identify the gas law described by each activity.
iii.
Complete the calculations necessary to evaluate the gas law in each activity.
iv.
From your results, derive a single mathematical relationship that relates pressure,
volume, temperature, and number of molecules.
The purpose of this investigation is to conduct a series of experiments, each of which
illustrates a different gas law. You will be given a list of equipment and materials and
some general guidelines to help you get started with each experiment. Four properties of
gases will be investigated: pressure, volume, temperature, and number of molecules. By
assembling the equipment, conducting the appropriate tests, and analyzing your data and
observations, you will be able to describe the gas laws, both qualitatively and
mathematically.
40
Properties of Gases Safety
Always wear proper personal protective equipment (i.e., your goggles and lab coat).
Always wear proper attire: long pants/skirt with no holes, shoes that completely cover
your feet, and keep long hair tied back.
Gloves must be worn while handling chemicals. However, gloves must not be worn in the
hallways or when interacting with non-chemical entities (e.g., door handles, eyes, or
laptops/cell phones). Remove gloves before exiting the lab unless transporting chemicals
with the aid of an ungloved partner to open doors.
Place your backpacks, skateboards, etc. on the counter in the back of the lab. It is
important that people don’t trip and fall when working around hazardous chemicals. You
may not wear headphones in the lab because they distract you from your environment
created a hazardous lab space.
Waste Disposal
All waste is water which can be poured down the drain.
Disposable face masks can be thrown in the regular trash.
41
Properties of Gases Experimental Procedures
Part I. Pressure and Volume
In this experiment, you will study the relationship between the volume of gas and the
pressure it exerts while keeping the amount of gas and temperature constant.
1. Assemble the LabQuest by plugging it in and connecting the Gas Pressure Sensor to
Channel 1 of the interface. Turn it on by pressing the start button.
2. Take a 20 mL syringe and position the front edge of the piston at the 15 mL mark. This
will be the volume of air trapped in the barrel of the syringe for the first run.
3. Attach the syringe to the valve of the Gas Pressure Sensor, as shown in Figure 1. A
gentle half turn should connect the syringe to the sensor securely. Important: Read
the volume at the front edge of the inside black ring on the piston of the syringe, as
indicated by the arrow in Figure 1.
Figure 1: Gas Pressure Sensor Experimental Setup
4. Setup the data collection system to Time-Based mode. Data points or values should
be recorded after 60 seconds, once the system equilibrates. Once ready, press the
play button and record your observations. Save this as run 1.
5. While the syringe remains connected to the sensor securely, push on the piston of the
syringe to decrease the volume of air trapped inside the syringe by 2 mL (at 13 mL).
Hold the piston in place and record the pressure of the air in the syringe at this volume
in your lab notebook.
6. Repeat step 5 three more times, pushing the piston in by 2 mL each time. Record the
pressure at 11, 9, and 7 mL in the lab notebook.
7. Plot and graph the points in the spreadsheet provided in Canvas.
Part II. Pressure and Absolute Temperature
In this experiment, you will study the relationship between the absolute temperature of a
gas sample and the pressure it exerts while keeping the volume and amount of gas
constant.
42
1. Connect the Temperature probe to channel 2 of the interface of the LabQuest and
discard the values from Part 1. Make sure the values from Part 1 are already in
your lab notebook.
2. Assemble the apparatus shown in Figure 2 using a 600 mL beaker and a 125 mL
Erlenmeyer flask. Be sure all fittings are airtight by screwing the plastic tubing and the
Luer-lock valve to the rubber stopper. Twist the valve to the closed position. Make
sure the rubber stopper and flask neck are dry, then twist and push hard on the rubber
stopper to ensure a tight fit.
Figure 2: Pressure and Absolute Temperature Experimental Setup
3. For the cold-water bath, pour 150 mL of water in the 600 mL beaker. Place the flask
inside the beaker that contains the water. Make sure you hold the flask down so it
remains submerged in the water.
4. Pour ice in the beaker containing the flask slowly until it barely reaches the neck of
the flask. Avoid getting the rubber stopper wet. Place the temperature probe in the
beaker as shown in Figure 2. The temperature should be between 0 °C and 10 °C.
Wait at least 60 seconds (or until the pressure and temperature readings stabilize).
Once stabilized, record the temperature and pressure readings on your lab notebook.
5. Dump the cold water out of the beaker and dry the flask.
6. Pour 300 mL of room temperature water into the 600 mL beaker. Place the dry flask
inside the beaker. Hold down the flask so it remains submerged in the water. The
temperature should be between 20 °C and 30 °C. Wait at least 60 seconds (or until
the pressure and temperature readings stabilize). Once stabilized, record the
temperature and pressure readings on your lab notebook.
7. Discard the water in the beaker and dry the flask.
8. Pour 300 mL of hot water into the 600 mL beaker. Place the dry flask inside the beaker.
Hold the beaker down so it remains submerged in the water. The temperature should
be between 60 ºC and 70 ºC. Wait at least 60 seconds (or until the pressure and
43
temperature readings stabilize). Once stabilized, record the temperature and pressure
readings on your lab notebook. DO NOT discard the hot water.
9. For the final observation, wait for the temperature of the water to be between 40 ºC
and 50 ºC. Once the temperature is reached, submerge the flask in the beaker. Wait
at least 60 seconds (or until the pressure and temperature readings stabilize). Once
stabilized, record the temperature and pressure readings on your lab notebook.
10. Discard the water in the beaker. Disassemble the apparatus and dry the glassware.
11. Graph the temperature and pressure readings using the Excel spreadsheet provided
on Canvas.
Part III. Volume and Absolute Temperature
In this experiment, you will study the relationship between the volume of a gas sample
and its absolute temperature. Using the apparatus shown in Figure 3, you will place a 125
mL Erlenmeyer flask containing an air sample in a water bath and you will vary the
temperature of the water bath. Data collection will be done as before. Collect the data
pair simultaneously from the Gas Pressure Sensor and Temperature Probe, and then
record the volume on your lab notebook. Even though the pressure reading will not be
plotted on the graph of volume vs. temperature, it is important for pressure to be
monitored so that it can be kept constant.
1. Assemble the apparatus shown in Figure 3. Be sure all fittings are air-tight. Make sure
the rubber stopper and flask neck are dry, then twist and push hard on the rubber
stopper to ensure a tight fit. Be sure that the Luer-lock is opened to the large 60 mL
syringe and the volume reads 20 mL.
Figure 3: Volume and Absolute Temperature Experimental Setup
2. Fill the pitcher almost halfway with tap water and insert the assembled apparatus.
Place the pitcher containing the flask in a large storage bin. This will catch any water
overflow from the pitcher. Then, fill the rest of the pitcher with hot water to reach 4544
50°C, until it begins to overflow. Hold the apparatus in place by the barrel of the
syringe, not the plunger since it will rise to stabilize pressure. Important: The water
level must be equal to or higher than the gas level in the syringe (see Figure 3).
Once the experiment begins, the apparatus must not be removed from water
and the pressure should be kept constant. Wait 5 five minutes or until pressure is
constant (within 0.1 or 0.2 kPa) before taking the reading so that the apparatus can
get acclimated to the water bath. Collect your data for 60 seconds and record your
measurements on the lab notebook for volume and temperature from that last reading
(not the average provided in the screen).
3. For the following readings, the temperature should be decreased by ~5 ºC. Add small
handfuls of ice to reach the desired temperature. Stir the solution in the pitcher
vigorously until the ice dissolves and check the temperature. Repeat as needed. When
the suggested temperature is reached and the pressure remains constant (+/- 0.5
kPa), collect data for 60 seconds.
Important: If the syringe is not adjusting by itself after 20-30 seconds, slightly press
the plunger until pressure matches or gets close to initial pressure (Step 3) then
collect the temperature, and volume measurements. If you encounter any
problems, consult your GSA.
4. Repeat step 3 for a total of five increments. The minimum solution temperature should
be between 25 and 29 ºC.
5. To find the total volume of air in the apparatus, first measure the volume of air in the
flask by filling it with water until it reaches the rubber stopper. Pour the water into a 50
mL graduated cylinder. Record this value. For the estimated volume of the tubing
(from the rubber stopper to the Gas Pressure Sensor box), as well as in the valve
below the bottom of the syringe, use a value of ~4 mL. Finally, add the values from
the volumes of the flask, plastic tubing, and syringe all together to calculate the total
volume.
6. Graph the values of temperature and volume using the Excel Spreadsheet from
Canvas.
45
Properties of Gases Data Sheet
Name_______________________________________________________________
Section___________________
Date_____________________
Part I: Pressure and Volume
Volume (mL)
Pressure (kPa)
15
13
11
09
07
Part II: Pressure and Absolute Temperature
Temperature (ºC)
Temperature (K)
Pressure (kPa)
Part III: Volume and Absolute Temperature
Volume in
the
syringe
(mL)
Total Volume
(mL)
Temperature
Range (ºC)
(refer to step
6)
Actual
Temperature
(ºC)
Pressure
(kPa)
45-50
40-44
35-39
30-34
25-29
Complete the following table:
Laws
Variables
α , 1/ α
Constants
Boyle
Charles
Gay-Lussac
Write an equation using the two variables using k as the proportionality constant (i.e. P
= k x V is direct, or P = k/V if inverse.
46
Properties of Gases Report Requirements
Standard Report Requirements
Each student will write a short report for this experiment. Write everything in your own
words. Do not copy or rephrase what somebody else writes. Type the report using
justified alignment, double spacing, 1-inch margins, and Times New Roman 12-point font
or Arial 11-point font. It should include the following sections:
Header, objectives, procedures, data and results, analysis, calculations, and discussion.
Experiment Specific Requirements
You must include all graphs from the excel spreadsheet with a brief description of each
one. You must also include the tables associated with each graph with a brief description
of the table.
Discussion Questions
1. Consider the filling of a scuba tank. At constant temperature and volume, what
would be the expected effect on pressure (P) if the number of moles of gas n is
increased. (5 pts.) Given: The Ideal Gas Law equation is PV=nRT.
2. Why is Kelvin the unit for temperature in the ideal gas law equation? Why is Celsius
not used in the ideal gas law equation? (5 pts.)
3. In Part III, as you placed the apparatus in the warm water bath, you should have
noticed the volume of air in the syringe increased. What variable in the ideal gas
law remained constant? (5 pts.) Given: The Ideal Gas Law equation is PV=nRT.
47
Properties of Gases Report Rubric
Section
Formatting
3 points
Prose
1 point
Grammar
1 point
Header
2 points
Objectives
2 points
Procedures
1 point
Criteria
Full Credit
Half Credit
No Credit
Follows report
guidelines
(justified text,
double-spaced,
1-inch margins,
single
font/color/size).
The student
followed all
formatting
guidelines.
The student
did not follow
The student did formatting
not follow one
guidelines.
or two
The student
formatting
did not follow
guidelines.
three or more
formatting
guidelines.
The report is
written in prose or
paragraph form
(i.e., no bulleted
lists and no
numbered lists).
The report
was written
entirely in
prose.
The report
contains some
prose and
some lists.
No prose or
paragraphs.
Correct English
grammar,
spelling, and use
of the third
person (i.e., no I,
you, we, etc.)
No more than
5 typos or
grammatical
errors. The
student uses
the third
person.
No more than
10 typos or
grammatical
errors. Some
use of personal
pronouns.
Barely
readable.
Follows header
guidelines
(student name,
lab partner(s)
name, date the
experiment was
performed, lab
title).
All header
guidelines
were followed.
The student
did not follow
The students
header
did not follow
guidelines.
one or two
The student
header
did not follow
guidelines were
three or more
not followed.
header
guidelines.
The objective is a
brief description
of the purpose of
the experiment.
The student
understands
what the
experiment
was about and
why they did it.
The student
does not quite
show
understanding
of the
experiment.
No objective
included. The
objective
does not
make sense.
Writes
procedures were
followed as
written in the lab
notebook.
Includes
standard entry
unless
significant
changes were
made.
The student
includes
insignificant
changes.
Includes a
detailed
procedure or
does not
include this
section at all.
48
Data &
Results
12 points
Types up all of
the tables and
data collected in
the Lab. Includes
figures.
This section
Calculations includes typed
examples of all
5 points
designated
calculations.
Analysis
8 points
Discussion
Question 1
5 points
Discussion
Question 2
5 points
Tables are
appropriately
labeled (each
correctly
identified,
appropriate
title, and units
are included),
and data is
complete.
Required
figures are
also included.
Includes a
typed example
of all
calculations
performed.
Units are
included.
Data doesn’t
match the Lab
notebook.
Tables are
presented
incorrectly or
not adequately
labeled. Data
makes no
sense,
etc.
A picture or
image of the
data sheet or
notes taken is
given as data
results (i.e.,
screenshots
of the
Benchling lab
notebook).
You are
missing most
or all data
and results.
A picture or
image of the
Some
data sheet or
calculations are
notes taken is
missing, OR
given as
units are
calculations
missing.
OR none
included.
Includes a
Brief but thorough separately
labeled
explanation of
section with an
results, trends,
explanation of
and what they
results, trends,
mean.
and what they
mean.
Some trends
are explained
or missing or
inadequate
explanation.
No analysis
included. The
student writes
procedure as
analysis.
At constant
temperature, if n
represents the
moles of gas
present, what
would be the
Identifies the
expected
relationship.
relationship
between pressure
(P) and the
number of moles
of gas (n).
Not applicable.
Answer is
either correct
or incorrect.
No answer
included, or
answer does
not make
sense.
From your plot of
pressure vs.
temperature, why
is the unit of
temperature in
the gas equation
Explains why
an absolute
scale (Kelvin)
is used OR
what would
happen if the
No answer
included, or
answer does
not make
sense.
Explains why
an absolute
scale (Kelvin)
is used and
what would
happen if the
49
reported in
Kelvin? What
would happen if
degrees Celsius
were used?
Discussion
Question 3
5 points
In Part III, as you
placed the
apparatus in the
warm water bath,
you should have
noticed the
volume of air in
the syringe
increased.
Explain what has
happened to the
gas. What
variable should
have remained
constant?
Celsius scale
is used.
Celsius scale is
used.
Explains what
happened and
what variable
remained
constant.
No answer
Explains one or included, or
the other but
answer does
not both.
not make
sense.
50
Experiment 4: Beer’s Law
Experiment 4:
Beer’s Law
51
Beer’s Law Introduction
OBJECTIVES
Prepare and measure the absorbance of five standard nickel(II) nitrate solutions.
Plot a standard curve from the data obtained from the standard solutions.
Measure the absorbance of a nickel(II) nitrate solution of unknown concentration.
Calculate the concentration of the unknown Ni(NO3)2 solution.
Background
Visible spectroscopy involves shining light on a sample that causes no change to the
solution. Colored solutions have interested chemists for a long time. When colored
solutions are irradiated with “white” light they selectively absorb light of some
wavelengths, but not others. When this happens, the absorbed light disappears and the
remaining light (lacking this color) contains the remaining mixture of non-white light
wavelengths. A color-wheel (below) shows approximate complementary relationships
between wavelengths absorbed and what we see. For example, a green substance,
absorbs red light (the complementary color).
Image from: http://sustainable-nano.com/2015/07/07/fruit-colors/
We can determine the wavelength or group of wavelengths absorbed by exposing the
solution to monochromatic light of different wavelengths and recording the responses. If
light of a particular wavelength is passed through a sample and does not reach the
detector, we will see that the intensity of the transmitted light (I) is significantly less than
the intensity of the light incident on the sample (Io). The percent transmittance is then
defined as the percent of the incident light that passes through the sample such that
52
%T = (I/Io) x 100
(1)
The Beer-Lambert law shows that the molar solution concentration (c) is linearly related
to the log of the ratio of the transmitted and incident light, equation 2, where l is the length
of sample cell (usually 1 cm) and ε is the molar absorptivity, which is a constant for each
particular molecule.
log(Io/I) = εcl
(2)
This equation is often written in terms of absorbance (A), equation 3.
A = εcl
(3)
With this equation (or a calibration curve based on it), you can (a) determine the
concentration of an unknown solution or (b) estimate what the absorbance of a certain
solution will be as long as three of the four values in the equation are known.
The primary objective of this experiment is to determine the concentration of an unknown
nickel (II) nitrate solution. You will use a Vernier SpectroVis spectrometer to measure the
concentration of each solution. In this experiment, light from the LED light source will pass
through the solution and strike a photocell. A solution of higher concentration absorbs
more light (and transmits less) than a solution of lower concentration. The spectrometer
monitors the light received by the photocell as percent transmittance.
You will prepare five nickel (II) nitrate solutions of known concentrations (these are called
standard solutions). Concentration is related to the amount of a substance (nickel (II)
nitrate) per volume of water. The typical unit of concentration in chemistry is “molarity,”
abbreviated “M.” If you are not familiar with molarity concentrations, that’s OK. Just
understand that the molarity of nickel (II) nitrate in a solution is proportional to the amount
of nickel (II) nitrate in the solution. The more added, the higher the concentration.
Each solution is transferred to a small, rectangular cuvette that is placed into the
spectrometer. The amount of light that penetrates the solution and strikes the photocell
is used to compute the absorbance of each solution. You will plot absorbance (y-axis) as
a function of concentration (x-axis) to get a linear standard curve. Using this standard
curve, you will determine the concentration of an unknown Ni(NO3)2 solution by
measuring its absorbance with the spectrometer. You can either use the graph or linear
regression obtained from the standard curve information to find the concentration of the
unknown solution.
53
Beer’s Law Safety
Always wear proper personal protective equipment (i.e., your goggles and lab coat).
Always wear proper attire: long pants/skirt with no holes, shoes that completely cover
your feet, and keep long hair tied back.
Gloves must be worn while handling chemicals. However, gloves must not be worn in the
hallways or when interacting with non-chemical entities (e.g., door handles, eyes, or
laptops/cell phones). Remove gloves before exiting the lab unless transporting chemicals
with the aid of an ungloved partner to open doors.
Place your backpacks, skateboards, etc. on the counter in the back of the lab. It is
important that people don’t trip and fall when working around hazardous chemicals. You
may not wear headphones in the lab because they distract you from your environment
created a hazardous lab space.
Waste Disposal
Dispose of all waste in the oxidizer waste container labeled OX.
Disposable face masks and gloves can be thrown in the regular trash.
54
Beer’s Law Experimental Procedures
1. Obtain 15-20 mL of 0.30 M nickel (II) nitrate (Ni(NO3)2) solution in your 25 or 50 mL
graduated cylinder.
See the video Measuring Stock Solutions for assistance.
(http://youtu.be/bu-r6dAaId0) Pour this into a 100 mL beaker.
2. Fill a different 100 mL beaker half full with DI water.
3. Label five clean, dry, test tubes 1-5.
4. Prepare five standard solutions according to the chart below using two droppers. Make
sure you don’t mix up your two pipettes – use one for Ni(NO3)2 and another for the
distilled water. Thoroughly mix each solution with a stirring rod. Clean and dry the
stirring rod between uses. Refill your 10 mL graduated cylinders with either Ni(NO3)2
solution or water as needed. See the video SE1 Nickel (II) Nitrate: Dilutions for
assistance. (http://youtu.be/sO0f7uGkKgs)
Test tube 0.30 M Ni(NO3)2 Distilled H2O
number
(mL)
(mL)
1
1.0
4.0
2
2.0
3.0
3
3.0
2.0
4
4.0
1.0
5
5.0
0
5. Connect a Spectrometer to the USB channel of the Vernier LabQuest unit. Connect
the LabQuest unit to the spectrometer using the USB cable. Turn on the LabQuest
unit. View the video How to Start the Lab Quest Unit and Spectrometer for assistance.
(http://youtu.be/OCK1PbrZZEE)
6. Calibrate the spectrometer.
a. Prepare a reference (or “blank”) sample by filling an empty cuvette ¾ full with
distilled water.
55
b. On the LabQuest unit, tap the reddish-orange meter box and select Calibrate.
The following message appears in the Calibrate dialog box: “Waiting …
seconds for lamp to warm up.” After the allotted time, the message changes
to: “Finish Calibration”. View the video How to Calibrate the Spectrometer for
assistance. (http://youtu.be/S-Pu3G85kew)
c. Place the blank in the cuvette slot of the spectrometer. Notice that the cuvette
has two different sides, a smooth side (left) and a ridged side (right). Make
sure that the smooth side with the arrow at the top is facing the side of the
spectrometer’s cuvette slot with the arrow and light bulb.
d. Select “Finish Calibration”.
When the message “Calibration Completed”
appears after several seconds, select OK.
7. You are now ready to collect absorbance-concentration data for the five standard
solutions. First, you must select the wavelength of light to analyze. See the video
How
to
Measure
Absorbance
of
a
Solution
for
assistance.
(http://youtu.be/hvQ3_MqiNZA)
a. Empty the cuvette and rinse it twice with small amounts (< 1 mL) of nickel (II) nitrate solution from test tube 1. Fill the cuvette 3/4 full with the solution and place it in the spectrometer. Collect used nickel (II) nitrate solution in a beaker at your workstation to dispose of in the satellite waste area at the end of the experiment - do not pour the solutions down the drain. b. Start the data collection by tapping the green arrow in the bottom of the screen. A full spectrum graph of the solution will be displayed. c. Stop the data collection by tapping the red square at the bottom of the screen. 56 d. Review the graph to identify the peak absorbance value. Use the stylus or the left and right arrow keys to move the cursor to a wavelength of 659 nm (or as close as possible). e. Write down the absorbance and concentration values on your data sheet. f. Empty the cuvette of the used nickel (II) nitrate solution into your beaker at your workstation to dispose of in the satellite waste area at the end of the experiment - do not pour the solutions down the drain. g. Rinse the cuvette with DI water. All rinse water should be collected in your beaker. 8. Repeat step 7 with the remaining standard solutions. Record the absorbance and concentrations of each solution on your data sheet. 9. Graph the data to determine the linear best fit curve for your data. This step can be done after lab. 10. Determine the concentration of the unknown Ni(NO3)2 solution. a. Record the unknown ID number in your lab notebook. b. Obtain about 5 mL of the unknown Ni(NO3)2 solution. See the video Measuring Stock Solutions for assistance. (http://youtu.be/bu-r6dAaId0) c. Measure the absorbance as you did for the standard nickel (II) nitrate solutions in step 9. d. Use this absorbance value and the best fit equation from step 9 to solve for the unknown concentration. This step can be done after lab. 11. Clean your cuvette by rinsing it with water. All rinse water should be collected in your beaker. 12. The collected nickel (II) nitrate solutions and rinse water should be disposed of in the oxidizer waste container labeled OX. 57 Beer’s Law Data Sheet Name_______________________________________________________________ Section___________________ Trial Date_____________________ Concentration (mol/L) Absorbance at 659 nm 1 2 3 4 5 0.30 Best-Fit line equation 6 Unknown ID ____ 58 Beer’s Law Report Requirements Standard Report Requirements Each student will write a short report for this experiment. Write everything in your own words. Do not copy or rephrase what somebody else writes. Type the report using justified alignment, double spacing, 1-inch margins, and Times New Roman 12-point font or Arial 11-point font. It should include the following sections: Header, objectives, procedures, data and results, analysis, calculations, and discussion. Experiment Specific Requirements Create a graph of absorbance vs. concentration. Add a linear trendline and show the equation. After the graph is complete, copy the graph into your lab report and lab notebook. Do not make graphs by hand, and do not put screenshots or pictures of your graph in your lab report. You must provide the graph and data table in your report to receive full credit. Discussion Questions Copy these questions into the lab notebook for perusal during the lab. Answer these questions in prose (complete sentences, paragraph form) in the lab report. 1. Assume you have two different unknown nickel (II) nitrate solutions in your lab. Without using a spectrometer or any other instrument, how could you estimate which of the unknown nickel (II) nitrate solutions is more concentrated, relative to each other? (5 pts) 2. The color of a cobalt (II) nitrate solution is red. Would you be able to use your nickel (II) nitrate calibration curve to calculate an unknown concentration of cobalt (II) nitrate? Justify your answer. (10 pts) 59 Beer’s Law Report Rubric Section Criteria Full Credit Half Credit No Credit Formatting 3 points Follows report guidelines (justified text, doublespaced, 1-inch margins, single font/color/size). The student followed all formatting guidelines. The student did not follow one or two formatting guidelines. The student did not follow formatting guidelines. The student did not follow three or more formatting guidelines. Prose 1 point The report is written in prose or paragraph form (i.e., no bulleted lists and no numbered lists). The report was written entirely in prose. The report contains some prose and some lists. No prose or paragraphs. Grammar 1 point Correct English grammar, spelling, and use of the third person (i.e., no I, you, we, etc.) No more than 5 typos or grammatical errors. The student uses the third person. No more than 10 typos or grammatical errors. Some use of personal pronouns. Barely readable. Header 2 points Follows header guidelines (student name, lab partner(s) name, date the experiment was performed, lab title). All header guidelines were followed. The students did not follow one or two header guidelines were not followed. The student did not follow header guidelines. The student did not follow three or more header guidelines. Objectives 2 points The objective is a brief description of the purpose of the experiment. The student understands what the experiment was about and why they did it. The student does not quite show understanding of the experiment. No objective included. The objective does not make sense. Procedures 1 point Writes procedures were followed as written in the lab notebook. Includes standard entry unless significant changes were made. The student includes insignificant changes. Includes a detailed procedure or does not include this section at all. Data & Results 7 points Types up all of the tables and data collected in the Lab. Includes figures. Tables are appropriately labeled (each correctly identified, Data doesn't match the Lab notebook. Tables are presented A picture or image of the data sheet or notes taken is given as data 60 appropriate title, and units are included), and data is complete. Required figures are also included. incorrectly or not adequately labeled. Data makes no sense, etc. results (i.e., screenshots of the Benchling lab notebook). You are missing most or all data and results. A picture or image of the data Includes a typed example of all calculations performed. Units are included. Some calculations are missing, OR units are missing. Includes a separately labeled section with an explanation of results, trends, and what they mean. Some trends are explained or missing or inadequate explanation. No analysis included. The student writes procedure as analysis. Discussion Question 1 5 points Assume you have two different unknown nickel (II) nitrate solutions in your lab. Without using a spectrometer or any other instrument, how could you estimate which of the unknown nickel (II) nitrate solutions is more concentrated, relative to each other? The student explains their estimation process. Student demonstrates partial understanding. No answer included, or answer does not make sense. Discussion Question 2 10 points The color of a cobalt (II) nitrate solution is red. Would you be able to use your nickel (II) nitrate calibration curve to calculate an unknown concentration of cobalt (II) nitrate? The student understands Beer’s Law and clearly explains the application. The student understands how Beer’s Law can be applied but misunderstood the question. No answer included, or answer does not make sense. Calculations 10 points This section includes typed examples of all designated calculations. Brief but thorough explanation of Analysis 8 points results, trends, and what they mean. sheet or notes taken is given as calculations OR none included. 61 Justify your answer. 62 Beer’s Law Calculations Step 1: Calculate the concentrations of your dilutions. (C1V1=C2V2) C1 = the concentration of Ni(NO3)2 used V1 = the volume of Ni(NO3)2 C2 = this is what you are solving for V2 = the total volume of solution Example: C1 = 0.50M Ni(NO3)2 V1 = 5.0 mL C2 = ? V2 = 5.0 mL 2 = 1 × 1 0.50M Ni( 3 )2 × 5.0 = = 0.50 Ni( 3 )2 2 5.0 Step 2: Plot absorbance vs concentration. Example graph. A = εl • c + 0 ↓ ↓ ↓ ↓ y=m•x+b = − − = Use this calibration curve to solve for concentration by plugging in the measured absorbance of the unknown. 63 Experiment 5: Determining the Enthalpy of a Chemical Reaction Experiment 5: Determining Enthalpy 64 Determining Enthalpy Introduction Thermochemistry is the branch of chemistry that describes energy changes occurring during chemical transformations. Chemical reactions and phase changes are two notable chemical transformations. As chemical bonds break and form in a chemical reaction, energy in the form of heat (qrxn) is either released or absorbed by the reaction (the system). It is difficult to measure the heat exchange between reactants and products (the system) directly. However, considering that energy cannot be created or destroyed (1st law of thermodynamics) we can assume that the energy lost/gained during a chemical transformation is opposite in sign, but equal in magnitude, to the energy gained/lost by the surroundings: 0 = qgained + qlost (1) -qlost = qgained (2) Therefore, we can indirectly measure the heat transfer of the system by measuring the heat transfer that occurs between the system and surroundings. Calorimetry is the measurement of heat associated with a chemical or physical process. The heat exchanged between the system and surroundings can be measured when the chemical or physical change occurs in a calorimeter. A calorimeter is an object which has a known heat capacity determined via calibration. Given that the heat capacity of the calorimeter is known, any temperature change made to the calorimeter can be converted to an amount of heat associated with the chemical/physical process responsible for this temperature change. It is important to define the system in calorimetry as the materials undergoing the chemical/physical change, and the surroundings as the components of the calorimeter responsible for absorbing heat from the system or providing heat to the system In this experiment, you will determine enthalpy changes of chemical reactions (ΔHrxn) using “coffee cup” calorimetry. Coffee cup calorimetry is performed under constant pressure (isobaric conditions) due to the system being open to the atmosphere. When pressure is held constant, the heat (qrxn) released or absorbed during a reaction is equal to the enthalpy change of the reaction (ΔHrxn). The derivation of why qrxn = 65 ΔHrxn at constant pressure exceeds the scope of this experiment but is shown for your own understanding below. From the First Law of Thermodynamics the change in internal energy of a system: ΔUsys = q + w (3) Chemical reactions are generally associated with the potential to do electrical work and work of expansion. The former refers to the potential for a chemical reaction to provide an electric current whereas the latter refers to work being done on the surroundings when the volume of a system expands during the reaction. Given that there is no significant electric work done by driving an electric current through an external wire, work of expansion should be considered in calorimetry. The work by expansion is the product of the pressure acting against the system and the volume change in the system. In this case, the expression carries a negative convention as the internal energy Usys decreases because energy is lost to perform work on the surroundings: wexpansion = - PΔV (4) Enthalpy (H) was defined to describe the change in heat of a chemical/physical process (system) while work is being done on it. Specifically, it is the sum of the internal energy needed to generate a system and the energy needed by the system to make room for itself by displacing its surroundings upon establishing its own pressure and volume. The change in enthalpy (ΔH) would be written as: ΔHsys = ΔUsys + Δ(PV) sys (5) When considering coffee cup calorimetry where a chemical/physical process occurs under constant pressure, Equation 5 can be written as: ΔHsys = ΔUsys + PΔVsys (6) ΔHsys = Δ(q + w)sys + PΔVsys (7) Using Equation 3 to rewrite ΔU: 66 Given that only wexpansion will be significant for the system, wexpansion may be treated as total Δwsys and Equation 4 can be used to rewrite Equation 7 as: ΔHsys = Δqsys + (- PΔV)sys + PΔVsys = Δqsys (8) Thus, one primary advantage of coffee cup calorimetry is that the enthalpy change (ΔHrxn) can be determined directly from heat change (Δqrxn) due to constant pressure conditions. The calorimeter insulates the reaction (system) from its surroundings. If heat is released, the reaction is exothermic and ΔH will be negative (Figure 5-1). If heat is absorbed, the reaction is endothermic and ΔH will be positive (Figure 5-2). It is important for calorimeters to offer a nearly adiabatic boundary. The term adiabatic implies there is no pathway for heat to enter or leave the calorimeter. This level of insulation allows for only the heat being released/absorbed by the system to be measured. Figure 5-1. Illustration of coffee cup calorimetry. When the chemical/physical process is exothermic, ΔH = (-), and the heat released by the system to the surroundings increases the temperature of the solution. 67 Figure 5-2. Illustration of coffee cup calorimetry. When the chemical/physical process is endothermic, ΔH = (+), and the heat absorbed by the system from the surroundings decreases the temperature of the solution. In this experiment, you will determine enthalpy changes (ΔHrxn) of chemical reactions using “coffee cup” calorimetry. If we conduct a reaction between two substances in an aqueous solution, then the heat gained or lost by the solution can be calculated with the following equation: qsoln = msol × Csol × ∆Tsol (9) The term qsoln represents the heat that is gained or lost by the solution, msol is the mass of the solution, Csol is the specific heat of the solution, and ∆Tsol is the temperature change of the solution. This experiment will use water as the solvent of the solution. The value of 4.18 J / g ºC may be used as the specific heat of water. Polystyrene cups (Styrofoam™) are good insulators and thus are suitable container components of the calorimeter used in this experiment. The resistance to temperature change or overall quantification of an insulator’s performance can be quantified using thermal conductivity. The thermal conductivity of the polystyrene cup is 68 approximately 0.06 BTU. The thermal conductivity of the glass used to construct your beaker is approximately 1.82 BTU. A smaller quantity for implies the material is a stronger insulator. Thus, polystyrene cups are superior insulators to your glass beakers. However, they may still absorb some of the heat released by a reaction. Thus, the heat transfer from the system to both the water surroundings and the polystyrene cup surroundings should be considered. The heat absorbed by the polystyrene cup can calculated by the following equation: qcup = Ccup x ΔTsol (10) The term qcup represents the amount of heat absorbed by the polystyrene cup, Ccup is the calibrated heat capacity of the polystyrene cup, and ∆Tsol is the temperature change of the solution. The term Ccup is a value determined experimentally through calibration. The calibration measures the change of temperature of the polystyrene cup given known heat changes and further relates the value to ∆Tsol. The value of 22 J/ºC for Ccup has already been determined for you. The total heat of the calorimeter qcal includes the heat of all components and thus includes both qsoln and qcup: qcal = qsoln + qcup (11) Remembering the first law of thermodynamics and Equation 2: -qlost = qgained (2) Therefore, the sum of the heat gained/lost by the solution and the polystyrene cup is equal to the heat lost/gained by the reaction: qsoln + qcup = qcal = - qrxn (12) Since coffee cup calorimetry is performed under constant pressure conditions: 69 qrxn = ΔHrxn (13) In this experiment you will experimentally determine the enthalpy change of five reactions. The first three reactions are the acid-base reactions listed below. 1. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) 2. NaOH(aq) + NH4Cl(aq) → NaCl(aq) + NH3(aq) + H2O(l) 3. HCl(aq) + NH3(aq) → NH4Cl(aq) In addition to experimentally determining the ΔHrxn for each of these reactions, you can use Hess’s Law to determine the enthalpy change of reaction three above by manipulating reactions one and two to produce a net reaction. You will compare your calculated value of ΔHrxn for reaction three using values from reaction one and reaction two to your experimentally determined value of reaction three itself. Hess’s law states that the total enthalpy change of a reaction is the net sum of all changes. As long as reaction conditions such as temperature and pressure are kept constant, the pathway or number of steps to synthesize a product are independent of each other, and the product will have the same net enthalpy change. The best way to understand this concept is by reviewing the example below. Hess’s Law Example Consider the overall net reaction N2H4(l) + H2(g) → 2NH3(g) Reactions which may be considered as independent steps of the net reaction are shown below with their known net enthalpy change: i) N2H4(l) + CH4O(l) → CH2O(g) + N2(g) + 3H2(g) ∆H = - 37 kJ/mol ii) N2(g) + 3H2(g) → 2NH3(g) ∆H = - 46 kJ/mol iii) CH4O(l) → CH2O(g) + H2(g) ∆H = - 65 kJ/mol 70 Upon rearrangement of i)-iii) to produce the overall net reaction shown originally, the enthalpy changes of these independent reactions can be used to calculate the enthalpy change of the overall net reaction. The reaction labeled as “iii” will be flipped to list CH2O(g) and H2(g) as reactants. When the reaction is revered, its net enthalpy change is also flipped with regards to its sign: iii) CH2O(g) + H2(g) → CH4O(l) ∆H = + 65 kJ/mol With the rearrangement is “iii” the overall net reaction can now be obtained: N2H4(l) + CH4O(l) + N2(g) + 3H2(g) + CH2O(g) + H2(g) → CH2O(g) + N2(g) + 3H2(g) + 2NH3(g) + CH4O(l) By cancelling like terms on either side, the overall net equation is obtained: N2H4(l) + CH4O(l) + N2(g) + 3H2(g) + CH2O(g) + H2(g) → CH2O(g) + N2(g) + 3H2(g) + 2NH3(g) + CH4O(l) = N2H4(l) + H2(g) → 2NH3(g) Now that these steps have been arranged to create the overall net reaction of interest, the net enthalpy change of each step can be used to create the net enthalpy change of the overall net reaction: ∆H = (- 37 kJ/mol) + (- 46 kJ/mol) + (65 kJ/mol) = - 18 kJ/mol Thus, the net enthalpy change of the overall net reaction N2H4(l) + H2(g) → 2NH3(g) calculated to be -18 kJ/mol using the net enthalpy changes of other chemical reactions and the pathway to product formation did not affect its net enthalpy of formation. You will also determine ΔHrxn for two additional systems: (1) the dissolution of ammonium nitrate in water and (2) the redox reaction between magnesium powder and hydrochloric acid. 71 Determining Enthalpy Safety Always wear proper personal protective equipment (i.e., your goggles and lab coat). Always wear proper attire: long pants/skirt with no holes, shoes that completely cover your feet, and keep long hair tied back. Gloves must be worn while handling chemicals. However, gloves must not be worn in the hallways or when interacting with non-chemical entities (e.g., door handles, eyes, or laptops/cell phones). Remove gloves before exiting the lab. If transporting chemicals follow the one glove rule and use one gloved hand to carry the materials and one ungloved hand to touch common surfaces such as doorknobs. Place your backpacks, skateboards, etc. on the counter in the back of the lab. It is important that people don’t trip while working with hazardous chemicals. You may not wear headphones in the lab. Handle all reagents with care to avoid contact with skin. They may cause painful burns. If you accidentally spill a solution or get in contact with a solution, notify the GSA immediately. The GSA will help clean up the spill. If the solution used in this experiment contacts your skin, rinse the affected area with water for a minimum of 15 minutes. If you spill a solution on your gloves, remove the contaminated gloves immediately and retrieve a clean pair. m of 15 minutes. Waste Disposal Reaction 1: NaOH(aq) + HCl(aq) —> Waste container labeled non-regulated.
Reaction 2: NaOH(aq) + NH4Cl(aq) —> Waste container labeled Ammonia solutions.
Reaction 3: HCl(aq) + NH3(aq) —> Waste container labeled Ammonia solutions
Reaction 4: Dissolved Ammonium Nitrate —> Waste container labeled Oxidizer
Reaction 5: Mg(s) + 2 HCl(aq) —> Waste container labeled Acid
Gloves, disposable face masks, and all other non-chemical waste are disposed of in the
normal trash.
72
Determining Enthalpy Experimental Procedures
You will only perform each reaction once and this data will be your calorimeter #1 data.
The calorimeter #2 data will come from another group. Do not leave before getting this
data from another group.
Reaction 1. NaOH and HCl
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
1.
Nest two Styrofoam cups inside of each other to make your calorimeter. Add the
magnetic stir bar to the calorimeter (inner cup).
2.
Cover the opening of the calorimeter with the aluminum foil. With a pencil tip,
pierce a small hole close to the edge of the cup (Figure 1). The hole should be
small to avoid heat loss.
Figure 1
Figure 2
3. Assemble the ring stand, utility clamp, and stir plate as seen in Figure 2. Place
your calorimeter inside the ring holder and rest it on the stir plate.
4. Measure 25 mL of 2.0 M HCl solution with a graduated cylinder. Remove the
aluminum foil/or cup lid and pour the HCl solution into the calorimeter.
5. Tightly cover the top of the calorimeter with the aluminum foil/or cup lid.
6. Carefully insert the temperature probe through the punctured hole in the aluminum
foil/or cup lid (Figure 1). Secure the temperature probe with the utility clamp (Figure
2). Be careful not to puncture the bottom of the calorimeter.
73
7. Connect the temperature probe to Channel 1 of the LabQuest unit. Plug in the
LabQuest, turn it on, and set the data collection time to 180 seconds (3 minutes).
8. Turn on the stir plate. **The t…
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