FACULTY OF SCIENCE AND AGRICULTURE
SCHB022
PRACTICAL MANUAL
2023
Compiled by Mr Ramohlola KE
1
Table of Contents
i.
Safety Policy ............................................................................................... 4
General Laboratory Rules ............................................................................... 4
Toxicity of Chemicals ..................................................................................... 6
General Laboratory Rules for equipment and instrumentation ....................... 7
General SAFETY and LAB RULE Agreement .............................................. 8
ii.
Attendance at the Laboratory ...................................................................... 9
iii.
Missed Laboratory Sessions ................................................................... 9
iv.
General Information ............................................................................. 10
Title .......................................................................................................... 12
Abstract .................................................................................................... 12
Introduction (1-2 pages) .................................................................................... 12
Results ...................................................................................................... 13
Discussion ................................................................................................ 15
References ................................................................................................ 16
v.
Grading .................................................................................................... 16
vi.
Warning Against Plagiarism .................................................................... 16
vii.
Contact Persons .................................................................................... 18
viii. Practical Session 2023 Dates ...................................................................... 19
ix. Laboratory Equipments ................................................................................ 20
Experiment 1: Thermodynamics – Second Law ................................................ 22
Purpose: ........................................................................................................ 22
Introduction: ................................................................................................. 22
2
Procedures: ................................................................................................... 27
Data table 1: .................................................................................................. 30
Post Lab Questions: ...................................................................................... 32
Experiment 2: A General Chemistry Thermodynamics Experiment ................. 33
Introduction................................................................................................... 33
Materials ....................................................................................................... 36
Procedure ...................................................................................................... 36
Results .......................................................................................................... 37
Experiment 3: Adsorption of an Organic Acid from Aqueous Solution ............ 38
Object............................................................................................................ 38
Discussion ..................................................................................................... 38
Apparatus and chemicals required ................................................................ 42
Calculations: ................................................................................................. 43
Experiment 4: Distribution of a Substance Between Two Non-Miscible Liquids
........................................................................................................................... 45
Object............................................................................................................ 45
Discussion ..................................................................................................... 45
Method of procedure..................................................................................... 46
Results .......................................................................................................... 48
Calculations .................................................................................................. 48
3
i.
Safety Policy
It is critical that you prepare for each experiment by reading it
carefully before entering the laboratory. Not only will this ensure
that you get the maximum benefit of the experience, but it also
makes for a safer environment in the laboratory. This is important
not only for your own safety but also for those around you. A
number of policies have been developed in order to make sure that
the laboratory is safe and that it runs smoothly. In each experiment
specific hazards are indicated by bold type and procedures are
described that must be adhered to. Accidents commonly occur when
the following rules, as approved by the Chemistry Department
Safety Committee, are not followed.
General Laboratory Rules
DO NOT work alone in a laboratory. Know the location and proper
use of fire extinguishers, fire blankets, safety showers, eye wash
devices, and first aid kits.
DO NOT perform unauthorized experiments.
1. The following PPE (Personal Protective Equipment) must be
worn at all times in the laboratory:
•
Laboratory coat
4
•
Eye protection: Splash proof chemical goggles. If you do get
a chemical in your eye, rinse your eye immediately using large
quantities of water or an eye wash bottle
•
Closed shoes with socks must be worn at ALL times – open-
toed shoes, backless shoes, sling backs, clogs, and sandals are not
permitted.
•
Always wear gloves when working with unknown
substances.
•
Always wear the appropriate breathing masks when
working with toxic or irritating vapours.
•
Long hair and loose clothing must be confined while in a
laboratory
2. Observe good housekeeping practices. Work areas should be kept
clean and tidy at all times.
3. Eating, smoking, and drinking are not allowed in a chemistry
laboratory.
4. Labels and equipment instructions must be read carefully before
use.
5. Dispose of all chemical waste properly. Liquid and solid waste
containers must be properly used at all times.
5
6. Unused chemicals should not be returned to their original
container unless directed to do so by the lab assistant
7. Report any accident and/or injury, however minor, to your
demonstrator immediately.
8. Before leaving the laboratory, make sure your work area is clean
and dry and also ensure that all gas, water, vacuum, and air valves
are completely turned off.
9. Thoroughly wash your hands before leaving the laboratory
Toxicity of Chemicals
Laboratory work involves the use of a number of chemicals that are
potentially hazardous. Toxic chemicals can enter the body by
ingestion, skin absorption, and inhalation. Procedures that are
performed correctly have minimum risk. You are required to do the
following before working with any chemical substance:
•
Read the label and instructions on the chemical container
carefully
•
Make sure all the correct PPE are used when working with
any chemical substance
6
General Laboratory Rules for equipment and instrumentation
Follow the correct operating procedure for each instrument.
It is your responsibility to report malfunctioning equipment.
Do not use equipment that malfunctions or in your opinion may
endanger yourself or your classmates.
YOU ARE ULTIMATELY RESPONSIBLE FOR YOUR OWN
SAFETY AND THAT OF YOUR FELLOW STUDENTS,
WORKERS AND VISITORS
ARE YOU PREGNANT?
Please be aware that the lab is a dangerous environment when
pregnant. The Department of Chemistry is unable to guarantee you
that you will not be exposed to any teratogenic substances, i.e.
substances that can cause harm to your unborn child
If you are pregnant, the Department of Chemistry strongly
recommends you delay completion of the practical component of
your course until after the birth of your child and you have finished
breastfeeding. If you choose to continue with the practical
component, this is done entirely at your own discretion and the
Department of Chemistry assumes no responsibility for any dangers
to both you and your unborn child.
7
If you are pregnant, or if you should fall pregnant during the course
of your studies, please notify the Senior Lab Assistant immediately,
and provide supporting documentation from your General
Practitioner.
General SAFETY and LAB RULE Agreement
This is to confirm that I have read and that I understand the General
laboratory rules.
I also declare that I will obey and adhere to each and every rule
stated above.
I have received a duplicate copy of this paper and will keep it
available for review throughout my courses.
_______________
________
_____
Student name and student number
Signature
Date
You must sign the Safety Acknowledgement sheet before you work
in the lab. If you have questions about these rules and procedures,
please ask your Lab instructor before starting any laboratory work
in this course
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ii.
Attendance at the Laboratory
•
Students are required to attend the laboratories each week
and expected to be punctual for the laboratory sessions. Practicals
will held on Wednesdays.
•
The practical sessions are scheduled to begin at 12:00
online.
•
Students who arrive late for a laboratory session will not be
allowed to start the experiment and will be required to make up the
laboratory in accordance with the information below.
iii.
Missed Laboratory Sessions
Students are required to notify the laboratory coordinator within 48
hrs of missing a laboratory session. Students are required to make
up any excused absences e.g., those for which an official medical
note is provided to the Senior Laboratory Assistant. At the Senior
Laboratory Assistant’s discretion, you will be allowed to make up
other laboratory sessions that were missed for reasonable reasons.
All absences must be made within ONE WEEK of returning to the
university, and by prior arrangement with the Senior Laboratory
Assistant. No absences can be made up once the same graded work
has been returned to other students in the course.
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iv.
General Information
•
Practicals are designed to be an integrated part of the course,
they will help to explain and clarify certain points discussed during
lectures.
•
It is important that you put as much effort into the practicals
as possible as they will help with the rest of the course and as they
are examinable.
•
It is imperative that each student should be prepared for the
practical before he/she enters the laboratory. Read the practicals in
conjunction with your textbook(s).
•
The lecturer or the technical assistant must sign all results.
(Not by the demonstrators).
•
Each student must write his/her own report, unless stated
otherwise. A typed practical report (Arial 12, 1.5 spacing) must be
submitted at the beginning of the following week (Monday before
12h00). The signed results must be attached to the report as an
addendum. The format of the report is the following:
Lab Information
Before each lab session, you should prepare by reading the lab
manual and the textbook required reading. We expect you to have a
good understanding of the purpose, details of the procedure, the use
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of all chemicals and any significant hazards, and the underlying
science of the experiment when you come to lab. Each Pre-lab
recitation will have a prelab. Although your lab notebooks will not
be checked before lab drawing up tables in your lab notebook for
your data and carrying out the preparation calculations (e.g., mass
needed to make up solutions of given molarities) will help you
finish quickly and efficiently.
Report Format
Although you are not English majors, it is still very important to be
able to communicate your science to others. Writing poor enough
to be unclear or confusing will affect your grade, as will lack of
regard for grammar, punctuation, and spelling. Learn to use the
spell-check facility that is built into your word processing software.
Here are some general comments to help you with your scientific
writing.
Scientific writing is not literary writing. You should aim to be brief,
precise, and unambiguous. The reader should clearly understand
what you are trying to say. Try to keep your verb tense consistent
and appropriate. You may use either passive or active voice, but try
to be consistent. Avoid using jargon or slang and use full sentences.
It is rare that you would need to use first person; i.e., try not to refer
to “I”, “we”, “our”, “us”, nor should you speak about yourself, e.g.,
“the student”.
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Instructions for writing reports in Physical Chemistry
laboratory
The report should contain the following parts:
Title
Title of the experiment, your name and email address, date
Abstract
An abstract is a brief statement (not more than a paragraph) of the
results of the experiment and the method used. Quote actual values
for one or two of your most important results.
For example:
The rate constant for the reaction between x and y was determined
spectrophotometrically by monitoring the absorption of product z
at 500 nm as a function distance in a flow tube. A value of (0.82 +
0.02) L mol-1s-1 was obtained.
Introduction (1-2 pages)
This is a description of the purpose and the method of the
experiment. In this section also a basic principle of the phenomenon
should be explained. For example, it may be a brief description
about thermodynamics. You may explain what kind of information
12
you may get from the molecules with this method. What is the basic
principle of the measurement?
Results
This section includes a summary of the data and calculations
leading to the final results reported, along with the corresponding
estimates of uncertainty. All the essential items should appear in the
body of the report, usually in tabular form, though in a few cases a
plot of the raw data may be appropriate. Each item should be
accompanied by units and an estimate of uncertainty. Only minor
reductions (such as subtractions of weightings or burette readings)
should be carried out on the data sheet.
When multiple-step calculations are involved, it is helpful to make
a table with results from each of the major steps in a different
column. One sample illustration for each type of non-trivial
calculation should be shown. For each type of calculation, state the
equation, define the symbols used, show substitutions, and give the
calculated result accompanied by units and an estimate of
experimental error. The sample should also show how the error was
calculated. Arithmetic details should be omitted.
Carefully consider the number of digits carried in a calculation. You
must be sure to carry enough digits to preserve the accuracy of the
data. On the other hand, it only wastes effort and increases chances
for error to carry many meaningless digits. A good rule is to retain
13
one or two doubtful digits. The question as to which digits are
doubtful is determined from the estimated error. If you find after
making the error estimates that you have carried unnecessary digits,
you should round these off in the report. Estimates of experimental
error should be attached to the various table entries. If the error is
practically the same for all entries in one column, the estimate can
be placed at the head of the column or with the first entry.
Otherwise, errors should be given for several cases so as to illustrate
the variation. Error estimates should be rounded off to one or at
most two digits.
The error is given with an accuracy of one digit except when error
is smaller than 15 units. Then error is given with an accuracy of two
digits. The errors are always rounded upwards.
For example:
•
if the number is 32.21367 and its error is 2,34 the result should
be given as 32±3
•
If the error would be smaller like 0.124 then the result would
be 32.21±0.13
The number itself and the estimated error should be rounded off
consistently (e.g. 32.14 ±0.05)
It is recommended to use some computer program (eg. excel,
origin) for making graphs of you data. Include title of the figure
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and axis titles in the figure. If you have fitted the data by using
some function (eg. Linear regression or exponential growth)
include also the equation with the parameters of the best fit. Notice
that when you use a computer program for fitting your data the
program gives you also the errors for example for the slope and
the intercept in the case of linear regression.
Discussion
The discussion should include an evaluation of the quality of your
data and results. This is based partly on evidence within your own
data and experience, and partly on comparison of your results with
literature values.
Reviewing your own data, you should ask yourself whether the
internal consistency is as good as it should be according to the error
estimates made. Is there internal evidence of systematic error, for
example, a much larger discrepancy between parallel runs than the
apparent errors within each run? Are there unexpected trends in the
data? Comparing with the literature data, do you find that your
results agree as well as should be expected from your quantitative
error estimates? If not, do you see evidence of systematic error -for
example, are your points consistently low or high? Are there clear
trends in the errors? In any case, you should mention possible
systematic errors and other factors which might contribute
significantly to the error in the experiment but which were not
15
allowed for in your quantitative error estimates. When possible, you
should try to predict the directions of these errors. (For example, in
measurement of heat of solution, incomplete dissolving of the
sample will inevitably tend to give a low result.) In some cases, you
will need to consider the calculation carefully in order to predict the
direction of an effect on the final results.
References
References, except the lab handout, should be explicitly cited.
When information is obtained from a reference, that reference
should be noted by a number in brackets in the text (i.e.,[l]). At the
end of the report, the references are then given according to those
numbers. See any page in a scientific journal for examples.
v.
Grading
The final laboratory grade will account for 40% towards the final
course mark and the laboratory component will be evaluated as
follows:
Reports
: 50 %
Practical Test
: 50 %
vi.
Warning Against Plagiarism
Practical report sheets are individual tasks and not group activities
(unless explicitly indicated as group activities).
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Copying of text from other students or from other sources (for
instance the study guide, prescribed material or directly from the
internet) is not allowed – only brief quotations are allowed and then
only if indicated as such.
You should reformulate existing text and use your own words to
explain what you have read. It is not acceptable to retype existing
text and just acknowledge the source in a footnote – you should be
able to relate the idea or concept, without repeating the original
author to the letter.
The aim of the report sheet is not reproduction of existing material,
but to ascertain whether you have the ability to integrate existing
texts, add your own interpretation and/or critique of the texts and
offer a creative solution to existing problems.
Be warned: students who submit copied text will obtain a mark of
zero for the report and disciplinary steps may be taken by the
Department. It is also unacceptable to do somebody else’s work, to
lend your work to them or to make your work available to them to
copy – be careful and do not make your work available to anyone!
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vii.
Contact Persons
Position
Title &
Phone & Email
Names
Office#
&
Building
Senior
Mr. KE
Laboratory
Ramohlola
Assistant
015 268 3710
(Kabelo.ramohlola@ul.ac.za)
Office
No. 2022
(NBlock)
Lecturers
(SCHB022)
Prof MJ
Hato
015 268 4116
(mpitloane.hato@ul.ac.za)
and
and
Prof NC
015 268 2205
HintshoMbita
(nomso.hintshombita@ul.ac.za)
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Office
No. 1012
(NBlock)
Office
No. 2012
(NBlock)
viii. Practical Session 2023 Dates
SCHB022 (Physical Chemistry)
Practical
Date
1
23 August
2
06 September
3
13 September
4
20 September
Practical Test
11 October
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ix. Laboratory Equipments
20
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Experiment 1: Thermodynamics – Second Law
Purpose:
In this lab, we will exam the cooling processes of hot water and
validate the second law of thermodynamics.
Introduction:
Entropy is a measure of the numbers of ways the energy can be
distributed in a system of particles (molecules, atoms, or ions).
Particles in a system at equilibrium have the same average energy.
However, at a given instant of time, particle most likely have
different amount of energy. One particle may have certain amount
of energy at one instant, and at next, it could have more or less.
Depends on the energy the particle has; it will be able to access
different energy levels. The total amount of energy will determine
what energy levels are accessible to particles. Mathematically
Ludwig Boltzmann expressed entropy S, as:
S = k ln(W)
Where k is the Boltzmann constant = 1.38 x 10-23 J/K. W is the
numbers of ways the energy can be distributed in a system of
particles
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The Second Law of Thermodynamics states that entropy, or the
amount of disorder in the universe, increases each time energy is
transferred or transformed. Each energy transfer results in a certain
amount of energy that is lost— usually in the form of heat— This
heat energy can temporarily increase the speed of molecules it
encounters. As such, the more energy that a system loses to its
surroundings, the less ordered and the more random the
surroundings become.
Entropy and the Second Law of Thermodynamics describe a wide
range of occurrences in nature and engineering. A refrigerator is
essentially a heat pump and removes heat from one location at a
lower temperature, the heat source, and transfers it to another
location, the heat sink, at a higher temperature. According to the
second law, heat cannot spontaneously flow from a colder location
to a hotter one. Thus, work, or energy, is required for refrigeration.
A campfire is another example of entropy change in real life. The
solid wood used as fuel burns and turns into a disordered pile of ash.
In addition, water molecules and carbon dioxide gas are released.
The atoms in the vapors spread out in an expanding cloud, with
infinite disordered arrangements. Thus, the entropy changes from
burning wood are always positive. The released heat from the
burning woods heats up the surrounding and makes the entropy of
the surroundings increase, therefore, the entropy of the universe
increases. That is why burning wood is a spontaneous Process.
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Thermodynamic second law can also be demonstrated in a classic
food web. Herbivores harvest chemical energy from plants and
release heat and carbon dioxide into the environment. Carnivores
harvest the chemical energy produced by herbivores—with only a
fraction of it representing the original radiant energy from the sun—
and release heat energy with carbon dioxide into their surroundings.
As a result, the heat energy and other metabolic by-products
released at each stage of the food web have increased its entropy.
Think about gas trapped in a container with known volume,
pressure and temperature as the system. The gas molecules can have
an enormous number of possible configurations. If the container is
opened, the gas molecules escape, and the number of configurations
increases dramatically, essentially approaching infinity. If in the gas
expansion process, there is no energy exchange between the gas
molecules and its surrounding, the system become the universe.
Thus, ΔS, or the change in entropy for the universe is greater than
zero. Thus, the gas expansion process is spontaneous.
Similarly, entropy also increases when hot water is left at room
temperature and allowed to cool down. In this experiment, we will
explore how to measure the change in entropy of the universe during
a cooling experiment. And calculate the free energy change for the
water in the cooling process.
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Before learning how to do the experiment and gather data, let's learn
some laws and equations that allow us to calculate temperature
change and increase in entropy during cooling experiments.
Newton's Law of Cooling states that the rate of temperature change
of an object is proportional to the difference between its own
temperature and the temperature of the surroundings.
𝑑𝑑𝑑𝑑
𝛼𝛼(𝑇𝑇𝑆𝑆 − 𝑇𝑇)
𝑑𝑑𝑑𝑑
Where T is the temperature of the object, Ts is the temperature of
the surroundings. Using calculus, this relationship can be converted
into this equation,
𝑇𝑇(𝑡𝑡) = 𝑇𝑇𝑠𝑠 + (𝑇𝑇0 − 𝑇𝑇𝑠𝑠)𝑒𝑒−𝑘𝑘𝑘𝑘
where lower case t represents time, Ts denotes temperature of the
surroundings, T0 is the initial temperature of the object, T(t) is the
temperature of the object at time t, and k is a constant that depends
on the characteristics of the object and its surroundings.
Using this equation, one can calculate the temperature of a cooling
system at any time if all the other variables are known. This
equation also shows that temperature is an exponential function of
time. Thus, when a hot object, like a glass of hot water, is placed in
a cooler environment, its temperature will decrease at an
exponential rate until it reaches the temperature of the surroundings.
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Entropy is a "state property," which is a quantity that depends only
upon the current state of the system. Quantities that are state
properties do not depend on the path by which the system arrived at
its present state. Therefore, the most useful way to quantify a state
property is to measure its change.
Now, let's see how to calculate the change in entropy, or ΔS. When
talking about entropy, we must first define the system. In this
experiment, the system is the water, the surroundings are the air in
the room. So the change in entropy of the universe, or ΔSuniverse is a
sum of the change in entropies of these individual components,
assuming there is only energy exchange between water and air.
ΔSuniverse = ΔSwater + ΔSair
Mathematically, the change in entropy is defined as heat gained or
lost, denoted by q, divided by the temperature, T, in Kelvin.
∆𝑆𝑆 = −
𝑞𝑞
𝑇𝑇
This equation can be applied to both the water and the air. When
using this equation for water, then q is the heat lost by water and T
is the temperature of water in Kelvin. When using this equation for
air, then q is the heat gained by air and T is the temperature of air in
Kelvin. We know that the hot water will cool spontaneously to the
surrounding temperature. Heat leaves water, or q has a negative
26
sigh for water, thus ΔSwater is negative. Entropy of water decreases.
On the contrary, the surrounding air gains heat or q has a positive
sign for air. Therefore, ΔSair is positive. Entropy of the air increases.
From the second law of the thermodynamics, we know that the
change in entropy of the universe must be positive for a spontaneous
process. We will calculate the ΔSuniverse at various recorded
temperatures.
In this experiment, we will test these theoretical predictions of
Newton's Law of Cooling and the second law of thermodynamics.
Procedures:
1. Hold the thermometer in the air for 2 minutes, or until the
reading is stable. Record the temperature as the temperature
of the air in data table 1. (1 point)
2. Fill a beaker with between 500 mL to 1000 mL of water.
Record the mL of water used in data table 1 (1 point)
3. Place the beaker with water on a stove and heat the water to
boiling. Once the water boils, turn off the stove.
4. Carefully remove the beaker from the stove, and place it on
the table on top of few layers of paper towels. The paper
towels will act as insulation between the water and the cool
table. That makes the universe consists of only two parts, the
water and the air. Measure the temperature of the water
27
using the thermometer. Record the temperature as the
temperate of water at 0’00’’
5. Start the stopwatch and record the temperature of the water
every minute for the first 20 minutes in data table-1. (1
point)
6. For the next 20 minutes, record the temperature every 5
minutes in data table-1. (1 point)
7. For the rest of the time, record the temperature every 10
minutes in data table-1. (1 point)
8. Stop taking measurements when the water has come close to
room temperature measured in step 1.
9. Calculate the temperature change, ∆T for water for the first
time-interval by subtracting the temperature of water at
0’00’’ (0 minute 0 second) from that at 1’00’’, record ∆T as
the temperature change at 0’00’’.
10. Calculate the ∆T for the rest of time intervals.
11. Using 𝑞𝑞 = (𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑜𝑜𝑜𝑜 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 𝑖𝑖𝑖𝑖 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔) ×
4.18 𝐽𝐽
𝑔𝑔.𝑜𝑜 𝐶𝐶
calculate q of water. Record it in data table 1.
× ∆𝑇𝑇 to
12. Using qair = – qwater to calculate the q for the air and record it
in data table 1. (2 point)
13. Using ∆𝑆𝑆 =
𝑞𝑞𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤
𝑇𝑇
to calculate the ∆S for water, make sure
convert the temperature of water to Kelvins and record it in
data table 1. T is the temperature of the water. (1 point)
28
14. Using ∆𝑆𝑆 =
𝑞𝑞𝑎𝑎𝑎𝑎𝑎𝑎
𝑇𝑇
to calculate the ∆S for air, make sure
convert the temperature of water to Kelvins and record it in
data table 1. T is the temperature of the air. (1 point)
15. Using ∆Suniverse = ∆Swater+ ∆Sair to calculate the ∆S of the
universe and record it in data table 1. (1 point)
16. Using ∆Gwater = – T∆Suniverse to calculate the free energy
change for water and record it in data table 1. T is the
temperature of water. (1 point)
17. Manipulate the Newton law of cooling,
𝑇𝑇(𝑡𝑡) = 𝑇𝑇𝑠𝑠 + (𝑇𝑇0 − 𝑇𝑇𝑠𝑠)𝑒𝑒−𝑘𝑘𝑘𝑘
We get 𝑙𝑙𝑙𝑙
(𝑇𝑇(𝑡𝑡)−𝑇𝑇𝑠𝑠 )
(𝑇𝑇𝑂𝑂 −𝑇𝑇𝑠𝑠 )
18. Calculate 𝑙𝑙𝑙𝑙
= −𝑘𝑘𝑘𝑘
(𝑇𝑇(𝑡𝑡)−𝑇𝑇𝑠𝑠 )
(𝑇𝑇𝑂𝑂 −𝑇𝑇𝑠𝑠 )
at various time, t, and record it in data
table 1. (1 point)
19. Plot 𝑙𝑙𝑙𝑙
(𝑇𝑇(𝑡𝑡)−𝑇𝑇𝑠𝑠 )
(𝑇𝑇𝑂𝑂 −𝑇𝑇𝑠𝑠 )
versus time and the slope is –k
20. Use the k from step19 and Newton’s law of cooling, 𝑇𝑇(𝑡𝑡) =
𝑇𝑇𝑠𝑠 + (𝑇𝑇0 − 𝑇𝑇𝑠𝑠)𝑒𝑒−𝑘𝑘𝑘𝑘 to calculate the predicated T(t) at various
time, t and record it in data table 1. (2 point)
21. Then, plot the measure temperature T(t) from data table 1,
and the predicted T(t) from step 20 vs time, t, in minutes in
the same graph. Attach the graph to your lab report. (1
point)
29
22. Plot ∆Suniverse, ∆Swater and ∆Sair vs time, t, in the same graph.
Attach the graph to your lab report. (1 point)
23. Plot ∆Gwater vs time, t. Attach the graph to your lab report.
(1 point)
24. All the graphs must have the corresponding title, name of
the axis. Try use excel to do all the calculations.
Data table 1:
Air
Temperature
________________
_______________________
Kelvins.
Volume of water used. ________________ mL
Mass of water used. Assuming density of water is
1.0 g/mL.
________________ grams
30
o
C,
Time
Measured
Measured
Temp. of
Temp
Water
Change of
(oC)
Water
q of water
(J)
q of air (J) Swater
(J/K)
(oC)
0’00’’
1’00’’
2’00’’
3’00’’
4’00’’
5’00’’
6’00’’
7’00’’
8’00’’
9’00’’
10’00’’
11’00’’
12’00’’
13’00’’
14’00’’
31
Sair
Suniv.
Gwater
(J/K)
(J/K)
(kJ)
𝑇𝑇(𝑡𝑡) − 𝑇𝑇𝑠𝑠
𝑙𝑙𝑙𝑙(
𝑇𝑇0 − 𝑇𝑇𝑠𝑠
)
Post Lab Questions:
1. Does your experimental result validate the second law of
thermodynamics? Explain. (1 point)
2. A refrigerator, which is essentially just a heat pump, is also
a classic example of the second law. Refrigerators move heat
from one location at a lower temperature (the "source") to
another location at a higher temperature (the "heat sink"),
explain how that works. (1 point)
32
Experiment 2: A General Chemistry Thermodynamics
Experiment
Introduction
A common problem in general chemistry laboratory programs is
that, except for Hess, Law experiments, simple yet accurate
thermodynamics experiments are virtually impossible to perform
without resorting to bomb calorimeters or other expensive
laboratory experiment. This experiment provides the student
with the opportunity to do experimental thermodynamics, and to
calculate those thermodynamic values which usually cannot be
determined with the simple equipment available in a general
chemistry laboratory. The experiment consists of measuring the
voltage of a battery at different temperatures and requires items
common to most general chemistry laboratories: pH meter,
glassware, metal foil electrodes, and solutions of readily
available salts. The voltage measurements are made at room
temperature, in a cold-water bath and in a hot water bath. The
difference in voltage between the high and low temperature
measurements can be related to the change in entropy, ∆S, by the
relationship.
 ∂∆G 

− ∆S = 
 ∂T  P
(1)
33
where G is the Gibbs free energy and T is the absolute
temperature, at constant pressure, P.
This equation can be
written
− ∆S =
∆( ∆G )
∆T
(2)
since individual data points will be measured, and the
atmospheric pressure will be assumed to be constant. Using the
relationship between Gibbs free energy and the voltage of an
electrochemical cell
∆G = -nFE
(3)
substitution into eqn. (2) yields
− ∆S = −
∆nFE
∆F
(4)
∆S = nF
∆E
∆T
(5)
or
where F is Faraday's constant and n is the number of moles of
electrons transferred in the cell reaction.
The battery consists of Pb/Pb2+ and Cu/Cu2+ half-cells connected
by a salt bridge. When equal concentrations of the Pb2+ and Cu2+
34
solutions are used in both cells (0.50 M) the second part of the
Nernst equation becomes zero. Assuming the concentrations
(activities) of the Pb2+ and Cu2+ are equal, and assuming that
room temperature is 250C, the standard voltage of the cell will
be equal to the measured voltage and will be 0.463 V.
A temperature change of 55-600C should produce a voltage
change of 25-30 mV, a shift which is sufficiently large to be
measured on the mill volt scale of a standard pH meter. More
precise
and
extensive
work,
including
other
half-cell
combinations which have considerably less change in voltage,
could be accomplished on a pH meter with an expanded scale
capability; however, this equipment is not readily available in
most general chemistry laboratories. If sufficient standard pH
meters are available for each individual or team, many data
points can be collected while the battery is slowly heated or
cooled. The student can plot E versus T and determine ∆S from
the slope of the line, ∆E/∆T, and eqn. (5). If, as is more likely,
there is only one pH meter for every two or three teams, the value
of E can be determined initially at room temperature (E0 if room
temperature is 250C) and then at two widely separated values of
T (e.g., 75 and 100C).
35
Materials
The solutions were prepared with distilled water. The CuSO4,
Pb(NO3)2, and KNO3 were reagent grade chemicals, while the Pb
and Cu electrodes were, respectively, 3 mm sheets of 99% pure
metal and 12 mm electrical wire. The electrodes were cut to
about 15 cm. lengths. Backterioligical grade agar was used in the
salt bridges. Voltage measurements were made with a Beckman
Zeromatic SS-3 pH meter, with the zero set at midscale (pH7)
and the selector switch set to ± mV. The salt bridges were
prepared by dissolving agar (2% by weight) and KNO3 (10% by
weight) in water, heating until the mixture thinned, thickened,
then thinned again. The hot solution was poured into wet glass
U-tubes, and set up in 10-15 min.
Procedure
The half-cells are constructed by pouring 25-40 ml of CuSO4 or
Pb(NO3)2 solution into a short 50-ml test tube and placing the
appropriate electrode into the test tube. A third 50-ml test tube
is filled with 25-40 ml of an electrolytic solution of mixed
Pb(NO3)2 and KNO3. The test tubes are placed in a 600-ml
beaker, the salt bridges are added, and the pH meter leads are
attached to the electrodes with alligator clips. Because the SO42ions will migrate from the Cu2+ solution, through the salt bridge
and into the Pb2+ solution, an intermediate electrolytic solution
36
of 0.25 M Pb(NO3)2/0.50 M KNO3 is used. The salt bridges
connect the electrolytic solution to both the Pb/Pb2+ and Cu/Cu2+
half-cells.
When the half-cells are heated, the rate of ion
migration increases, but the presence of Pb2+ in the electrolytic
solution precipitates the majority of the SO42- ions as PbSO4 and
prevents them from reaching the Pb/Pb2+ half-cell.
After the room temperature measurement of E is taken and the
temperature is recorded, ice and water are added to the 600-ml
beaker to cool the cell. When the temperature has stabilized (510 min), measurements of E and T are recorded, and the solution
is warmed to ∼700C. The heating is stopped, and temperature
and voltage measurements are made again. The value of ε at
high and low temperatures are used in Eqn. (5) to determine a
value for ∆S.
Results
1.
Tabulate emf and T measurements.
2.
Calculate ∆G, ∆S and ∆H for your system.
37
Experiment 3: Adsorption of an Organic Acid from Aqueous
Solution
Object
To study the adsorption of an organic acid from aqueous solution
by charcoal and to determine the thermodynamic parameters.
Discussion
Adsorption in solid surfaces is a separation and purification
technology used in many industrial processes that has as its
objective removal of harmful or inconvenient substances. The
adsorption process involves the accumulation of the adsorbate
molecules on the external and interior surface of an adsorbent. This
superficial phenomenon involves interactions among three
components: adsorbent, adsorbate, and solvent. Usually, the affinity
between adsorbent and adsorbate is the main interaction force that
controls the adsorption. However, the affinity between adsorbatesolvent (solubility) can also influence the adsorption.
Adsorption from solutions is strongly affected by the polarity and
porosity of the adsorbent. The effect of porosity adsorbent depends
on the relationship between the dimensions of the pores’ adsorbent
and adsorbate molecules. In relation to the effect of polarity of the
adsorbent, polar adsorbent will tend to strongly adsorb polar
adsorbates and weakly adsorb nonpolar adsorbates, and vice versa.
38
In addition, polar solutes will tend to be strongly adsorbed from
nonpolar solvents (low solubility) and weakly from polar solvents
(high solubility) and vice versa. Organic acids are important
synthesis compounds in dies and pharmaceutical chemistry, being
also applied in conservation and disinfection in the food and tanning
industries. Low molecular weight organic acids are also important
pollutants since they are, themselves, the result of degradation of
bigger molecules from oxidation. Moreover, organic acids have
been found in atmosphere in gas, aqueous, and particulate phases,
in different environments. The organic acids present in the air can
be classified as primary or secondary pollutants. When emitted
directly from the sources they are considered primary and when
they originate from reactions that occur between other species in the
atmosphere, they are called secondary pollutants. In general, these
acids originate from processes of fossil fuel burning, vegetation and
organic matter, bacteria, insects, and plant biosynthesis. Organic
acids are also emitted by vehicles and formed in situ during
photochemical reactions, which are the main causes of the
formation of acids in the atmosphere. Since the presence of organic
acids in wastewater and the atmosphere is significant, the objective
of this work was to study the adsorption behavior of acetic,
propionic, and butyric acids on modified and unmodified
montmorillonite clays through adsorption isotherms and their
thermodynamic parameters, enthalpy variation (∆H), entropy
39
variation (∆S), and Gibbs free energy variation (∆G) in solutions
with different concentrations and temperatures.
Adsorption Thermodynamics
Thermodynamic parameters of adsorption processes are easily
evaluated because adsorption is a temperature dependent process.
Thermodynamic considerations for adsorption experiments are
required in order to establish the spontaneity and feasibility of such
processes. Therefore, experimental data obtained from adsorption
procedures are employed to determine thermodynamic parameters
such as Gibbs free energy change (∆G0) and change in enthalpy
(∆H0), change in entropy (∆S0).
Gibbs Free Energy of Change (∆G0)
Gibbs free energy of change is used to evaluate the spontaneity and
feasibility of adsorption processes. A negative ∆G0 value validates
a spontaneous process while a positive ∆G0 value is indicative of a
non-spontaneous process.
The free energy change in an adsorption process is usually related
to the equilibrium constant by the Gibbs fundamental equation.
∆G0 =−RT ln KC
(1)
40
where
R
=
Universal
gas
constant
(J.mol−1∙Kg−1∙K−1) T = Temperature (K) KC
= Equilibrium constant.
This equation measures the changes in equilibrium constant with
variations of temperature.
Enthalpy Change (∆H0)
Change in enthalpy (∆H0) can be described as the energy supplied
as heat at constant pressure when the system does no extra work.
Enthalpy change is typically measured with a calorimeter by
monitoring the temperature change that happens at constant
pressure. In adsorption study enthalpy change gives an insight into
the nature and mechanism of adsorption processes and it is usually
determined from the Van’t Hoff equation.
ln 𝐾𝐾 =
∆𝑆𝑆 ∆𝐻𝐻
−
𝑅𝑅
𝑅𝑅𝑅𝑅
where R = Universal gas constant (J∙mol−1∙K−1), T = Temperature
(K). K is the distribution coefficient (mL.g-1), defined as:
𝐾𝐾 =
𝑐𝑐𝑎𝑎
𝑐𝑐𝑒𝑒
Ca = Amount of adsorbate adsorbed at equilibrium (mg∙L−1)
Ce = Equilibrium concentration of adsorbate in solution (mg∙L−1).
41
A negative value of ∆H0 implies an exothermic adsorption process
while a positive ∆H value is indicative of an endothermic process.
Entropy Change (∆S0)
A change in entropy during an adsorption process can be
determined from the Vant’ Hoff equation, where a positive ∆S0
shows the affinity of the adsorbent towards the adsorbate, it also
suggests increased randomness at the solid/liquid interface with
some structural changes in the adsorbent and adsorbate.
Apparatus and chemicals required
Four stoppered 125 cm3 flasks, four 125 cm3 Erlenmeyer flask, one
50 cm3 volumetric flask, burette and holder, one 10 cm3 plus one 20
cm3 pipette, filter stand, two funnels, two 100 cm3 beakers, filter
paper, 1 g activated charcoal, approximately 0.4 mol dm-3 organic
acid, 0.1 mol dm-3 NaOH.
Method of procedure
In each of the four stoppered flasks, labelled 1 to 4, place exactly 1
g of charcoal. Place in each flask 50 cm3 of the 0.4 mol.dm-3 organic
acid solution made up (in the volumetric flask).
Shake each sample for at least 5 minutes, taking care to keep them
all at the different temperature for 30 minutes.
temperature of water.
42
Record
Filter the solutions and collect the filtrates in properly labelled
flasks. These solutions are now analyzed for the organic acid by
titration with NaOH; 10 cm3 aliquots.
Calculations:
1.
Calculate the molarity of your organic acid
2.
Calculate the volume of base required to neutralize the acid
initially present in each of the flasks and record this
volume as the "initial concentration". i.e. column Vi in
your table. Exact molarities of the organic acid and the
Alkali must be used.
Example: If molarity of the organic acid is 0.405 mol dm-3
and 25 cm3 was used, then moles of organic acid would be
0.405 mol dm-3 x 0.025 dm3. If the molarity of NaOH is
0.0996 mol dm-3, then the equivalent volume of NaOH in
cm 3 would be [(0.405 mol dm-3 x 0.025 dm3) ÷ (0.0996 mol
dm-3)]
This value represents the total amount of organic acid before
adsorption.
43
3.
Calculate the concentration of organic acid adsorbed and
determine the distribution coefficient.
6. Plot ln k gainst 1/T and determine the thermodynamics
parameters.
44
Experiment 4: Distribution of a Substance Between Two NonMiscible Liquids
Object
To determine the partition coefficient of benzoic acid between
water and benzene, and to test the validity of the distribution law
for this case.
Discussion
When a solute is shaken with two non-miscible solvents - if it is
soluble in each of them - it will distribute itself between the two
in accordance with the distribution law. If the solute is neither
associated nor dissociated in either solvent, the partition will take
place in accordance with the degree of solubility in each solvent
as follows: K = C1/C2
where K is the partition coëfficent and C1 and C2 refer to the
solubilities of the solute in the respective solvents.
If the solute is associated in one of the solvents, say solvent No.2
and is normal in the other, the formula is modified as follows:K = Cin / C2
45
where n is the degree of association, in the second solvent.
In investigating the distribution law, a number of systems may
be studied. When succinic acid distributes itself between ether
and water, it is found that the solute is normal in both liquids.
When benzoic acid distributes itself between water and benzene,
the solute is associated in one of the solvents.
For a more detailed discussion, read experiment 10 which deals
with the salicylic acid system.
Method of procedure
Place 25 cm3 of CO2 - free water and 25 cm3 of benzene in each
of three 50 cm3 separatory funnels and introduce 1.100; 1.500.
and 1.900 g of benzoic acid, respectively, into the numbered
funnels.
Stopper at once and shake for 15 minutes, holding the funnels by
the stem and neck in such a manner that the mixture is not
warmed by the hands.
Place separatory funnels in their supporting rings and allow the
mixture to separate into two perfectly clear layers.
Analyze the upper (benzene) layer in each of the funnels as
follows, taking care not to warm the liquids.
46
Place 25 cm3 of CO2 - free water and a drop of phenolphthalein
in each of two 125 cm3 Erlenmeyer flasks. By means of a 2 cm3
pipette withdraw and discard a sample from the upper layer in
funnel No.1., then place exactly 2 cm3 of this liquid in each of
the Erlenmeyer flasks.
Heat these solutions to boiling and titrate at once with 0.05 mol
dm3 NaOH solution, being careful not to overrun, the endpoint.
Should the two titrations not check to 0.05 cm3, take further
samples and repeat the titrations.
Having analyzed the upper layer in funnel no.1, analyze those in
the other two funnels in like manner.
Carefully draw about 17 cm3, of the lower (aqueous) layer from
the funnel no.1, running into a dry graduated cylinder. Rinse the
5 cm3, pipette with this solution, then run exactly 5 cm3, into each
of the Erlenmeyer flasks, add 20 cm3 of CO2 free water and a
drop of phenolphthalein to each, heat to boiling, and titrate with
0.05 mol dm3 NaOH solution.
After having obtained satisfactory "checks" (to 0.05 cm3) dry the
measuring cylinder and proceed to the analysis for the aqueous
layers in the other two funnels.
47
Results
Benzene layer
Aqueous layer
Sep.
Titre
funnel/cm3
/cm3
Ave
Sep.funn
Titre
el/cm3
/cm3
1. 2.00
1. 5.00
2. 2.00
2. 5.00
3. 2.00
3. 5.00
ave
N.B. Titre figures must coincide to 0.05 cm3. Otherwise repeat
titration.
Molarity of NaOH..........................
Calculations
1.
Write out the equation for the neutralization reaction
between benzoic acid and NaOH.
2.
Calculate the amount of benzoic acid in the aqueous and
benzene layers of each separating
3.
funnel.
Calculate the various ratio's for each separating funnel.
48
4.
Tabulate your results as follows:
Sep. funnel no.1
Cb =
Cw =
Sep. funnel no. 2
Cb =
Cw =
Sep. funnel no. 3
Cb =
Cw / Cb =
Cw / Cb =
Cw / Cb =
Cw2 / Cb =
Cw 2/ Cb =
Cw2 / Cb =
Cw / Cb2 =
Cw / Cb2 =
Cw / Cb2 =
Cw =
Which ratio gives a constant value and what inference can be
drawn from that?
49
50