all details belowhttp://eduweblabs.com/Database/Lab_Folders2/GIHeat…———————————————————————————————————————–Expt. 8
CALORIMETRY
INTRODUCTION:
All chemical and physical changes are accompanied by a corresponding transfer of energy, which is
usually seen as a transfer of heat. Heat may be either evolved (in an exothermic reaction) or absorbed
(in an endothermic reaction). Calorimetry is the name given to the technique used to measure the heat
change that occurs during a chemical or physical change. A calorimeter is the apparatus used to carry
out the experiment. A Styrofoam cup serves as an excellent calorimeter in the experiments that you will
carry out in this lab. When a coffee cup is used as a calorimeter, the heat change occurs at atmospheric
pressure, which is assumed to be constant for the duration of the experiment, and the heat change is
called the enthalpy of reaction, ∆H, at constant pressure.
Part I. Heat of Neutralization
When acids and bases neutralize each other, there is a corresponding exothermic heat change, which
can be measured by calorimetry. This heat is absorbed by the solution and is observed as an increase in
the temperature of the solution. Styrofoam being a good insulator, we may assume that the heat
absorbed by the Styrofoam and the surroundings is negligible. The heat absorbed by the solution is
given by
qsoln = msoln × ssoln × ΔT
where msoln is the mass of the solution, ssoln is the specific heat of the solution, and ΔT is the temperature
change of the solution.
The heat evolved by the reaction is given algebraically as:
– qrxn = + qsoln
where qsoln is the heat absorbed by the solution (note the positive sign), and qrxn denotes the heat
liberated by the neutralization reaction; the negative sign shows that heat is evolved during the
neutralization reaction. The enthalpy of neutralization, ΔHn, is then given by
Hn =
qrxn
n
where n is the number of moles of water formed during the neutralization. Note that for an exothermic
reaction, ΔH will have a negative value.
Part II. Heat of Solution
The dissolution of a salt in water can be an exothermic or endothermic physical change. When a salt is
dissolved in water contained in a Styrofoam cup, the heat absorbed or evolved during the dissolution is
reflected as a change in the temperature of the water. Again, assuming that the heat change of the
Styrofoam cup and surroundings is negligible, the heat evolved during an exothermic dissolution is given
by
– qsalt = + qwater
and qsalt may be calculated from the equation: qsalt = – (mwater × swater × ΔT)
where qsalt is the heat evolved when the salt dissolves in water (note the negative sign for an exothermic
dissolution), qwater is the heat absorbed by the water (note the positive sign), mwater is the mass of the
water, swater is the specific heat of water, and ΔT is the temperature change of the water.
Then the heat of solution may be calculated:
Hs =
qsalt
msalt
where msalt is the mass of the salt. ΔHs will be negative in this case.
For an endothermic dissolution,
+qsalt = –qwater
The positive and negative signs indicate that heat is absorbed by the salt when it dissolves and that heat
flows out of the water.
Then,
qsalt = – (mwater × swater × ΔT)
and,
Hs =
qsalt
msalt
But in this case, ΔHs will be positive.
PROCEDURE: The experimental procedure listed below has been performed in the laboratory and
recorded for your viewing. Your goal is to record the results from the information provided to allow
you to accurately complete your calculation sheet.
In this experiment, you will use a temperature probe that is interfaced to a computer data acquisition
system to record the temperature change that occurs during reaction. You will use a Styrofoam cup for a
calorimeter.
Then prepare the computer for data collection: Turn on the computer and one of the partners should
log in. Click on Start (the Windows logo at the bottom left of the screen). Scroll through the applications
and click on Vernier Software, and open Logger Pro 3.14.1. Click on File → Open → Chemistry with
Vernier. Click on Experiment 18 Hess’s Law. The vertical axis has temperature scaled from 15 to 400C.
The horizontal axis has time scaled from 0 to 200s.
Part I. Heat of Neutralization
1. Using a clean graduated cylinder, measure 25.0 mL of 1.0 M NaOH into a clean, dry, Styrofoam
cup. Make sure that you write down the exact molar concentration of the NaOH from the label
on the bottle.
2. Using another clean graduated cylinder, measure 25.0 mL of 1.1 M HCl and keep it ready (do not
add it yet).
3. Click on the Temperature label of the vertical axis and choose More… from the dropdown menu.
Manually scale the axis from 20 to 350C.
4. Carry out the reaction and collect the data:
a. Lower the tip of the Temperature Probe into the NaOH solution in the calorimeter and
gently stir the solution with the probe.
b. Click on the “Collect” button to start data collection.
c. After the same temperature has been recorded for about 10s, add the 50.0 mL of HCl to
the NaOH in the Styrofoam cup all at once, but be careful not to splash out any of the
solution. Keep stirring the mixture throughout the reaction.
d. Data collection will end after three minutes. However, if the same temperature is being
recorded past the 100s mark, you can end data collection by clicking on the “Stop”
button.
e. Click on the “Statistics” button (under the “Analyze” tab). Locate the minimum and
maximum temperatures given in the statistics box that pops up on the graph and record
them in your data sheet as the initial and final temperature respectively.
5. Dispose of the solution in the Styrofoam cup in the waste container, and rinse and dry the cup
carefully.
Print the graph before you prepare the computer for new data collection. Click on “Print Graph”.
Along with your and your partner’s name, type in the reactants (HCl +NaOH) in the comments
box. Do not print the Data Table.
You will have to prepare the computer for new data collection. Click on the “Experiment” menu
and click “Clear Latest Run”. Do not save the data.
6. Repeat the experiment, this time using 25.0 mL of 1.1 M HNO3 and 25.0 mL of NaOH. Print the
graph as before, this time typing in “HNO3 + NaOH” along with your and your partner’s names.
Part II. Heat of Solution
1. Prepare the computer for data collection. Manually scale the temperature axis from 0 to 400C.
2. Measure the mass (0.001g) of a clean, dry calorimeter. Using a clean, graduated cylinder, add
about 20.0 mL of distilled water to the calorimeter and measure the mass again.
3. Accurately weigh about 5g of salt X on a weigh boat and keep it ready. Make sure that you break
up any “clumps” of salt. This will make the salt dissolve faster and result in a smoother
temperature curve.
4. Carry out the reaction and collect the data:
a. Lower the tip of the Temperature Probe into the water in the calorimeter and gently stir
the solution with the probe.
b. Click on the “Collect” button to start data collection.
c. When the same temperature has been recorded for about 10s, carefully add all the salt
(do not spill or splash out the water), to the calorimeter, and continue stirring with the
probe for the duration of the experiment.
d. Data collection will end after three minutes. However, if the same temperature is being
recorded past the 100s mark, you may end data collection by clicking on the “Stop”
button.
e. Click on the “Statistics” button (one of the ‘quick-buttons’ located directly under the
menu headings). Locate the minimum and maximum temperatures given in the statistics
box that pops up on the graph and record them in your data sheet for the initial and
final temperature. Whether the final temperature is higher or lower than the initial
temperature will depend on whether the dissolution of the salt is exothermic or
endothermic.
5. Dispose of the solution in the Styrofoam cup in the waste container, and rinse and dry the cup
carefully.
Print the graph before you prepare the computer for new data collection. Along with your and
your partner’s name, type in “Salt X” in the comments box. Do not print the Data Table.
You will have to prepare the computer for new data collection. Click on the “Experiment” menu
and click “Clear Latest Run”. Do not save the data.
6. Repeat the experiment, this time using salt Y. Print out the graph as before, this time typing in
“Salt Y” along with your and your partner’s names.
LAB REPORT:
Turn in the data sheet with your calculations on a separate sheet of paper.
Calorimetry (Data Sheet)
NAME: __________________________________________
Part I. Enthalpy of Neutralization for an Acid-Base Reaction
HCl + NaOH
HNO3 + NaOH
1. Volume of NaOH
25.0 mL
25.0 mL
2. Volume of acid
25.0 mL
25.0 mL
3. Initial temperature from graph
___________
___________
4. Final temperature from graph
___________
___________
5. Exact molar concentration of NaOH
_____________________
Calculations
1. Volume of final mixture
2. Mass of final mixture (Assume the
density of solution is 1.00 g/mL)
50.0 mL
50.0mL
___________
___________
3. Specific heat of mixture
4.18 J/g·0C
4.18 J/g·0C
4. Temperature change, ∆T
___________
___________
5. Heat evolved, qrxn
___________
___________
Write balanced equations for the two acid-base neutralization reactions:
____________________________________________________________________
____________________________________________________________________
6. mol OH– reacted (limiting reactant)
___________
___________
7. mol H2O formed
___________
___________
8. Heat of neutralization, ∆Hn
___________
___________
Calorimetry Data Sheet (Continued)
Name _________________________________
Part II. Enthalpy of Solution for the Dissolution of a Salt
Salt X
Salt Y
1. Mass of calorimeter and water
___________
___________
2. Mass of calorimeter
___________
___________
3. Mass of salt
___________
___________
4. Initial temperature of water from graph
___________
___________
5. Final temperature of solution from graph
___________
___________
___________
___________
Calculations
1. Mass of water
2. Specific heat of water
4.18 J/g·0C
3. Temperature change, ∆T
___________
___________
4. Heat change of water
___________
___________
5. Heat change of salt
___________
___________
6. Enthalpy of solution (per gram of salt), ∆Hs
___________
___________
Post-Lab Question: Explain the similarity between the two heats of neutralization in Part I:
Enthalpy of Neutralization for an acid-base reaction.
Enthalpy of Solution
Calorimeter Constant
Cool Water + Hot
Cool Water + Salt
Water
Total Volume used (mL)
Mass of Final mixture (Assume
the density of solution is 1.00
g/mL)
Initial Temperature (°C)
Final Temperature (°C)
∆T (°C)
Specific heat of mixture (c)
4.18 J/g°C
Heat evolved [qsoln] (J)
Heat absorbed [qrxn] (J)
Show calculations for Heat evolved/absorbed below:
4.18 J/g°C
Reaction Data
Solid
Mass
Water Mass
Specific Heat of
(assume density Water
of soln. is 1.00
g/mL)
CaCl2
4.18 J/g°C
Na2CO3
4.18 J/g°C

LiCl
4.18 J/g°C
NH4NO3
4.18 J/g°C
NaCl
4.18 J/g°C
NaC2H3O2
4.18 J/g°C
∆T
Heat Change of
Water (qsoln)
Select one solid from above and show the complete calculations for Heat Change of Water
below:
Solid selected: __________

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