Lab Report: CalorimetryPurpose:The purpose of the Calorimetry experiment is to introduce you to application of thermochemistry. The purpose of writing the full lab report for Calorimetry experiment is to prepare you to write technical papers for journals, grants for funding, and learn to communicate scientific information to peers and the general public.Skills:In this lab report, you will:Analyze the data provided to you.Compose a full formal lab report (title page, objective, introduction, procedure reference, results and calculations section, discussion, and conclusion).Knowledge:This assignment will also help you to become familiar with the following important content information:CalorimetryWriting a complete lab reportTasks:This exercise asks you to collect, organize, analyze, and evaluate data you collected in the lab. You will type a lab report that includes the following: Title pageObjectiveIntroductionGive the logic of the experiment.Be sure to define key terms and all applied experimental equations (e.g. calorimetry, calorimeter, enthalpy of formation, heat capacity of calorimeter, heat, balanced chemical equations, Hess’ law, and percent error.).Procedure ReferenceIf there are any changes to the published procedure be sure to note them here.Results and Calculations sectionTable summarizingYour major experimental data (e.g. heat capacity of calorimeter, experimental heat of formation for Mg2+ & MgO, actual heat of formation for Mg2+ & MgO, and percent error)Be sure to include the PDF with the data that you were provided when you turn in your report. One sample calculation of each type.DiscussionWe did not record the boiling and freezing point of water experimentally. But issues with these measurements could possibly be something that would cause error in this experiment. Perhaps something related to this would provide one of your sources of error?State the heat of formation for MgO and describe any errors that may have led to an incorrect value of either the heat of formation (Mg2+ or MgO) or the calorimeter constant.ConclusionReiterate the major experimental data.Lab Results:Part A 4.184Trial 1 Trial 2 Trial 3 Trial 1 Trial 2 Trial 3Step 2: Mass of Dry Calorimeter (g) 19.8500 Starting Temp of tap waterStep2: Mass of Calorimeter + Tap water (g) 69.0861 69.7017 68.844 20.1 21.4 23.7Mass cold water49.2361 49.8517 48.994Step 3: Mass 250 mL beaker + 50 mL water (g) 167.3954 160.6936 164.2344 Starting Temp of hot waterStep 6: Mass of wet 250 mL beaker (g) 119.0842 112.3926 115.4384 51.3 50.4 53.3Mass of hot water48.3112 48.301 48.796Tfinal Tfinal Tfinal34.32522787 34.47973845 37.27556626Part BReaction of Mg with HCl Trial 1 Trial 2 Starting Temp of HClVolume of 1 M HCl added (mL) 98.6 99.9 21.3 21.9Mass of Mg (g) 0.5131 0.5070Final Temperature (oC) 43.3 45.0Reaction of MgO with HCl Trial 1 Trial 2 Starting Temp of HClVolume of 1 M HCl added (mL) 98.3 99.5 21.1 22.8Mass of MgO (g) 0.7897 0.8039Final Temperature (oC) 28.2 29.9I have attached a Calorimetry Lab Manual:Calorimetry-Measuring
EXPERIMENT 10
Heat of Formation
Part A: Introduction to Calorimetry
In Part A of this experiment is to detemine the heat capacity of a calorimeter. Once this valueis
known, your calorimeter can be used in Part B of the experiment to determine the heat of formation
of magnesium oxide.
All chemical and physical processes are accompanied by heat changes. The measurement of heat
changes in physical and chemical processes is called calorimetry. Heat changes maybemeasured
by carrying out the process in an insulated vessel where the heat exchange between the system
being observed and its surroundings is minimized. This type of system is called a calorimeter.
vessel contains a temperature measuring device and a magnetic stirring bar
The
insulated
The energy associated with the temperature changes in a substance can be expressed two ways.
is defined as the amount of energy in joules required to raise the temperature
Specific heat, Csp
of one gram of that substance
by one degree Celsius:
specific heat
Where q is the
quantity
of heat,
AT.c
sp
(EQ 10.1)
m(AToc)
is the temperature
change
in
degrees Celsius,
and
m
is the
mass of the substance in grams.
such as a particular calorimeter, is being
The term heat capacity, C, is used if a particular object,
as the amount of energy required to raise the temperature
defined
is
Heat
capacity
used repeatedly.
of that object one degree Celsius:
heat capacity
C,
AToc
(EQ 10.2)
so that you
of your calorimeter will be determined in this part of the experiment
“Determination of Enthalpy of Formation”.
the
in
experiment,
calorimeter
following
can use your
to determine the heat capacity of a calorimeter.
The following example illustrates this procedure
The heat
capacity
Chemistry 14! Grossmont College
10-107
Calorimetry-Measuring Heat of Formation
EXAMPLE 10.1 Determination of
Calorimeter Constant
A
sample of
tap water at 50.2 °C is mixed with 62.0 mL of
the calorimeter, whichwarm
is at 21.4 °C. The final
cooler tap water in
°C. The density of the water is
temperature of the system after
mixing is 33.7
1.00 g/mL, and the
specific heat of the tap water
is 4.184 J/
g°C. Determine the heat capacity, Cp, of the calorimeter
system.
| If there was no heat transfer from the hot water to the
all of the heat would be
in the liquid.
conserved
Therefore, all of the heat lost calorimeter,
heat gained by the cool water.
by the warm water would equal the
This, however, is not what is observed because
some of the
heat from the warm water is used to raise
the temperature
of the calorimeter system.
The change in
temperature is simply
50.0 mL
AT = Tinalinitial
(EQ 10.3)
As mentioned,
calorimeter,
the
heat, q, lost by the warm water is
gained by both the
hence the negative
and the
sign represents a heat loss and a positive cool water
sign is a heat gain
wam
Icool calorimeter
By substituting the expressions for
specific heat (equation
10.2), equation 10.4 can be
expressed as
(EQ 10.4)
10. 1) and heat
capacity (equation
-(ATwarm)(marm)(Csp)] [(aTcoo)mooCp)]+ C,(AT co1)
the
=
Using
data from this
(EQ10.5)
example gives:
ATeoo33.7 °C – 21.4 °C =12.3 °C
ATwarm
(EQ 10.6)
33.7 °C – 50.2 °C = – 16.5 °C
(EQ 10.7)
-16.5 C(so.og4.184
Now the heat
)-(a2.3-cN62.0g4.184
capacity of our calorimeter can
3452 J
3191
12.3c) (Ea 18.3)
be calculated:
J +C(12.3°C)
(EQ 10.9)
p21.2
Procedure: Part A
The
following operations
are
typical
for
determining
the heat
capacity
calorimeter. The temperature of a known mass of water is recorded; the
temperature should be approximately room temperature. Another sample of water, whose mass and
temperature is measured, is added to the first
water sample. The second water
sample should be approximately 50 °C higher than the
sample. By carefully monitoring the temperature
original
upon mixing the hot and cool water samples, we can detemine how much of the heat waschanges
transfered to the cool water and how much of
the heat was transferred to the
calorimeter; refer to equation Equation 10.4.
We will use
experiment.
a
temperature probe called a thermistor to
of
measure the
Your instructor will assist
you in setting up and
have collected your data with the
thermistor, we will use it to
temperature changes during
this
the thermistor. After
you
analyze the data.
operating
help
10-108
a
Chemistry 141 Grossmont College
Part B: Introduction to
Obtain
out
a
the
Measuring
the Heat of Formation of
Magnesium Oxide
calorimeter, a magnetic stir bar, a stirring plate and a thermistor. The temperature throughexperiment as a function of time will be tabulated during the experiment. Measure all
masses to the nearest 0.1 g and all temperatures to the nearest 0.1°C.
1.
While
one partner is
performing Step 2 the other should be preparing the thermistor apparatus as
directed by your instructor. Determine the accuracy of your thermistor by measuring the boiling
point of water and the freezing point of water.
a.
Half-fill a small beaker (e.g. 150 mL beaker) with water and bring to a boil. Read and
record the temperature of the boiling water.
b. Fill a medium beaker(e.g. 250 mL beaker) about one quarter full of tap water and add
approximately
100 mL of ice. Stir the mixture for about
temperature of the ice water.
one
minute. Read and record the
2. Wipe out any water orsolid debris from the inside of the calorimeter. Weigh the clean, dry calorimeterand stir bar, this is your calorimetry system. Measure 50.0 mL of tap water into a gradu
Weigh the contents
ated
cylinder and pour this into clean, dry pre-weighed calorimeterofsystem.
of the calorimeter after the water has been added to obtain the
water
transferred
a
mass
actually
to the cup. Place the cover on the calorimeter then insert the thermistor. Click Start on the
apparatus screen. Turn on the stirring plate and allow the system to reach a constant temperature.
3. Measure approximately 50 mL of tap watcr and pour it into a clean 250 mL beaker. Weigh the
its
record
mass. Gently heat the water to approximately 50-55 °C.
heat
your thermometer in the beaker and record the temperature of the
hot water. It is essential that you obtain the actual temperature of the hot water just before you
add the hot water to the calorimeter.
beaker and water and
Remove from
and place
this
4.
Add the hot water without
5.
The themistor apparatus will commence temperature and time measurements
Observe the temperature and time measurements until a maximum temperature has been
reached. Continue recording temperature and time readings until the temperature decreases by 2
°C below the maximum temperature or after 10 minutes have elapsed since the maximum temperature was observed.
splashing to the calorimeter. Stir gently to prevent splashing.
automatically
6. While you are waiting for the maximum temperature to be reached, weigh the empty (wet) beaker to obtain the actual mass of hot water that was added to the calorimeter. Be sure to use the
same balance each time that you weigh a particular piece of glassware. Compare this mass
to the mass of the water in the calorimeter.
7. Weigh the water in the calorimeter.
8. Repeat steps 2-6 at least two more times and calculate the average heat capacity and the standard deviation for your calorimeter.
9. Before beginning part B, calculate your calorimeter heat capacity and make sure that you have
reasonable values and good precision.
Part B: Introduction to
Magnesium Oxide
Measuring the Heat of
Formation of
In
heat of
B,
The heat capacity of your
calorimeter that you calculated from Part A will be used in this part of the experiment.
Part
the
formation of magnesium oxide will be determined.
The enthalpy of formation, AH, of a substance is the heat absorbed when one mole of it is
formed from the elements in their most stable forms at constant pressure. In some cases, elements
may be combined in a calorimeter to form the desired product and thus the AH may be measured
Chemistry 141 Grossmont College
10-109
Calorimetry-Measuring Heat of Formmation
directly. In other cases, the elements may not combine completely to form the desired product, or
there may be other difficulties with the direct determination. In these cases,
AH, may be obtained
indirectly by combining results from reactions that may be successfully measured:
AH
ZAH,° products -XAH° reactants
(EQ 10.10)
A direct determination of the AH, for Mg-” ion and an indirect determination for Mg0 will serve to
illustrate the possibilities.
Consider the reaction of magnesium and HCl:
Mgt 2 H aq)
H2(g+ Mg” (aq
(EQ 10.11)
AH, for H and H, are zero by definition under these conditions, the AH for this reaction
is the AH,for Mg*”. The variations in
temperature, pressurc, and concentration occuming dunng
this experiment will not cause
errors. So, the
would be the sum of the heat from
Since the
significant
the reaction of Mg and HCl and the heat from th
AH
=
AHn
e
calorimeter:
1oltion calorimeter)
(EQ 10.12)
limiting reagent
Using Equation
10.1, Equation 10.2, and Equation 10.12 allows
one
For MgO, the elements will combine directly, but the reaction is not
sured in a calorimeter, so an indirect approach will be followed.
to
calculate Al
easily accomplished
and
mea-
Consider the reaction of MgO with 1 MHC:
MgO+2H
H,0* Mg” (
(EQ 10.13)
The AH for this reaction willbe measured in your calorimeter. When this information is combined
with known values for AH of Mg” and H,Ou, the desired AH, value for MgO can be determined.
Calorimetry
If a reaction occurs in a calorimeter, the heat released during the reaction will be detected as an
increase in temperature, and the amount of heat will be the total heat capacity of the calorimeter and
its contents nmultiplied by the temperature change. The temperature change should be obtained by
taking data and graphing the temperature as a function of time from before the reaction until weil
is
after the
complete. A
apparatus will be used to capture the temperature
reaction
thermistor
changes during this process, the set-up and operations will be similar to that used in previously.
Depending on the type of calorimeter (i.e. coffee cup, aluminum, etc.) you will obtain heat capacity
values of approximately 18 J/Pc, 50 JPC, or100JPC. The heat capacities of Mg and Mg0 are negligiblysmallandcan be ignored. The 0.8 MHCI (the average value during reaction) has a specifñic
heat of 4.07Jg’°C’, and a density of1.01 g/mL.
10-110
Chemistry 141 Grossmont College
Part B: Introduction to
Measuring the
Heat of Formation of
Magnesium
Oxide

EXAMPLE 10.2 Determination of Heat of Reaction for Iron with
Hydrochloric Acid
A sample of 4.808 g of iron is reacted with 150.0 mL of hydrochloric acid. The initial
| temperature of hydrochloric acid was 21.75 °C. From the graph the maximum temperature
of the reaction was found to be 35.21 °C. The density of the hydrochloric acid solution is
1.01 g/mL, and the specific heat of the hydrochloric acid is 4.07 J/g°C. What is the enthalpy
of the reaction and enthalpy of formation of Fes” (aq)?
The net ionic equation for the reaction is:
Fe (t
2Ha)> Ha(tFe”
(EQ 10.14)
Using Equation 10.12 the enthalpy of the reaction can be found:
AH
rxn
AH
“Xn
=4solutiont4calorimete
limiting reagent
cI HciATHCI-Fe+CpATHC+Ee
(EQ 10.15)
lFe
The
temperature change for the reaction is
HCI+Fe
To find the
max-1inital
enthalpy
of the reaction
35.21°C-21.75°C = 13.46°C
plug
the data into
Equation
(EQ10.16)
10.15:
(150.0 mL1.01-4071346°C)-(21213.46°c)
AHxn

4.808 g
Fex
55.845 g Fe
9970 mol -99.7 kJ
mol
AH
(EQ 10.17)
mol Fe_)
(EQ 10.18)
|Using Equation 10.10 the enthalpy of Feag can be found:
AHpAH,° products- ZAH,° reactants
AH[AH° Fea+AH° H2 (g-[AH,° Fe(+2 AH,° H”(oql
The literature values for the
because they are all in their elemental state. So,
enthalpy of formation
for
H2 g
AHpn AH,° Fe” (ag)
AH
AH° Fea)-99.7 mol
H”
(ag), and Fe
(EQ 10.19)
are
al zero,
(EQ 10.20)
(EQ 10.21)
The literaturevalue of AH,° Fe”(aq is-89.1 ki/mol, which gives about a 10% eror.
Chemistry 14! Grossmon College
10-111
Calorimetry-Meas uring Heat of Formation
Procedure: Part B
Reaction of Mg with HCI
1. Be sure to use the same themistor as you did in “Heat Capacity of the Calorimeter.”
2. Weigh approximately 0.5 g of Mg to the maximum precision; record this mass in your note-
book.
3.
Add 100.0 mL of 1.0 M HCI to the calorimeter and
begin stirring. Click the Start button to
begin data collection. At this point you want to see the temperature stabilize and produce a
nearly straight line on the graph of the thermistor apparatus screen. This may take 2-5 minutes.
4.
Add the Mg and continue to stir. It is important that
you add the metal into the solution. Any
material that sticks to the sides of the calorimeter will introduce error into
your results. You wvill
notice the temperature increase on the display as the
reacts with the acid.
5. After the
Mg
temperature remains constant or begins to drop slowly (5-10 minutes), click Stop and
then Save Data.
6. Name your file with
a unique name and save it to a flash drive. You
want to obtain a graph in
which the final temperature has been obtained
by extrapolation of the first-order line-fit (see
Figure 10.1 on page 112).
FIGURE 10.1
Enthalpy of Magnesium with Hydrochloric Acid
Temperature (°C) vs. Time (minutes)
50
temperature
45
linear regression
40
Temp. 0C 35
30
25
20
10
15
Time (min)
Reaction of MgO with HCI
Weigh out approximately 0.8 g of MgO. Clean out the calorimeter from the previous reaction and
be sure to use a new aliquot of HCl for this reaction. Then
repeat the procedure given above for the
first reaction of Mg and HCI. Obtain a graph with the final
temperature calculated from the curve
fit function as before.
10-112
Chemistry 141 Grossmont College
Calculations and Data Treatment
Calculations and Data Treatment
1. In your discuss consider the accuracy of the thermistor. What was the recorded boiling point and
freezing point of water? How would a lower or high than expected value affect the other calculations in this experiment?
equal to
By definition AH°, for H’, 0, and H, are zero. Therefore, the AH
the AH for Mg2*. The AH for reaction 10.25 can now be determined using the data from reac-
for reaction 10.22 is
tions 10.22-10.24. AH for reaction 10.24 can be found in your text.
Mg+2H(ag)Mg”(agt Hz(e)
MgO+2Ha
2
Ha(+O2
Mga)+H,O
2
H,O (
Ms+%O2(> MgO
(EQ 10.22)
(EQ 10.23)
(EQ 10.24)
(EQ 10.25)
3. Make graphs and determine the corrected temperatures for each run. Be sure to completely and
corectly label all graphs.
4.
Calculate AH for each reaction using the amounts of reagents that you measured for your reac-
tions.
5. Calculate AH per mole of Mg and MgO for each trial.
6.
Calculate the percent error for each of your values.
7. Tabulate your values for AH, for Mg*” and MgO along with the literature values for each and
their percentage errors.
Grossmont College
Chemistry 141
10-113

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