OBJECTIVE

The aim of the experiment are to determine the heat capacity of calorimeter and to measure the

energy changes accompanying neutralization for weak and strong acids.

MATERIAL

1 M HCl, 1 M HC2H3O2 (acetic acid), 1 M NaOH

APPARATUS

Thermometers, Styrofoam cups, 50 mL graduated cylinders, square cardboard with hole in

center, split one-hole stopper, 250 mL beakers, 400 mL beaker, hot plate.

PROCEDURE

Part A : Heat Capacity of Calorimeter

1. A calorimeter is constructed similar to the one shown in Figure 1 by nesting Styrofoam

cups together.

2. A thermometer is placed into the hole of cardboard square and is stabilized by a split one-

hole rubber stopper.

3. 50.0 mL of tap water are placed in the calorimeter cup. The system are allowed to reach

equilibrium for 10 minutes. The temperature is recorded.

Figure 1: Simple calorimeter

4. 50.0 mL of hot tap water is placed exactly in in a 250-mL beaker. The water is heated

until the temperature is about 15°C - 20°C above room temperature.

5. The temperature of the hot water is recorded.

6. The hot water is poured into the calorimeter.

7. The lid of the calorimeter is replaced and the water is stirred carefully with the

thermometer.

8. The temperature of the water is recorded every 5 seconds for first 3 readings and every 15

seconds for next 2 minutes.

9. A graph of temperature as a function of time is constructed.

Part B : Heat of Neutralization of HCI-NaOH

1. The calorimeter and the thermometer are dried with a towel. 50.0 mL of 1.0 M NaOH

is measured and is added to the calorimeter.

2. The lid of the calorimeter is replace without thermometer.

3. 50.0 mL of 1.0 M HCI is measured exactly into a dry beaker. The beaker is allowed

to stand near the calorimeter for 4 minutes.

4. The temperature of the acid is recorded.

5. The thermometer is rinsed with tap water and is wiped till it dry.

6. The temperature of the base solution is recorded.

7. HCI and NaOH is added.

8. The solution is stirred carefully and the temperature is recorded every 15 seconds.

9. A graph of temperature as a function of time is constructed.

Part C : Heat of Neutralization of HC ₂ H ₃ O ₂ - NaOH

1. The procedure in Part B is repeated. 1 M HC₂H₃O₂(acetic acid) is used instead of 1.0 M

HCI.

DATA/RESULT

Part A : Heat Capacity of Calorimeter

Notation

Time,

s

Temperat

ure

Temperat

ure

Temperat

ure

Temperat

ure

°C(1) °C(2) °C(3)

°C

(Average)

Tequilibri

um - 25 25 25 25

t₀ 0 43 42 44 43

t₁ 5 31 30 30 30.3

t₂ 10 31 30 30 30.3

t₃ 15 32 31 31 31.3

t₄ 30 36 36 36 36

t₅ 45 36 36 36 36

t₆ 60 35 35 35 35

t₇ 75 35 35 35 35

t₈ 90 35.2 35.1 35.2 35.2

t₉ 105 34.5 34 34.5 34.3

t₁₀ 120 34.5 34.5 34 34.3

t₁₁ 135 34 34 34 34

Part B : Heat of Neutralization of HCl-NaOH

Part C :

Heat

Neutralisation

of HC ₂ H ₃ O ₂ -

NaOH

Notation Time, s Temperature,

Temperatur

e Temperature Temperature

°C(1) °C(2) °C(3)

°C

(Average)

Tequilibriu

m - 33 33 33 33

t₀ 15 33 33 33 33

t₁ 30 32 32 31 31.7

t₂ 45 32 31.5 31.6 31.7

t₃ 60 32 31.2 31.5 31.6

t₄ 75 31.5 31.1 31 31.2

t₅ 90 32 31 31 31.3

t₆ 105 31 31.2 31 31.1

t₇ 120 32 31 31.2 31.4

t₈ 135 31.7 31.1 30 30.9

t₉ 150 31 31 31 31t1₀ 165 31.5 31 30 30.8t1₁ 180 31 31 31 31

Notation

Time,

s

Temperatur

e

Temperatur

e

Temperatur

e

Temperatur

e

°C(1) °C(2) °C(3)

°C

(Average)

Tequilibriu

m - 28 27.8 28 27.9

t₀ 15 29 28 28.5 28.5

t₁ 30 28.3 28 29 28.4

t₂ 45 28.5 28 28.2 28.2

t₃ 60 28 28 28.2 28.1

t₄ 75 28 28 28.1 28.0

t₅ 90 28 28 28 28

t₆ 105 28 28 28 28

t₇ 120 28 28 28 28

t₈ 135 28 28 28 28

t₉ 150 28 28 28 28

t₁₀ 165 28 28 28 28

t₁₁ 180 28 28 28 28

SAMPLE OF CALCULATIONS

A) Heat Capacity of Calorimeter

1. Temperature of calorimeter and water before mixing = 25.0 °C

2. Temperature of warm water = 50.0 °C

3. Heat lost by warmer water = (Ti – Tf) x 50 g x 4.18 J/g.K

= [(52.0 + 273)– (35.2 + 273)]K x 50 g x 4.18 J/g.K

= 3511.2 J

4. Heat gained by cooler water = (Tf – Ti) x 50 g x 4.18 J/g.K

= [(35.2 + 273)– (25.0 + 273)]K x 50 g x 4.18 J/g.K

= 2131.8. J

6. Heat gained by the calorimeter = Heat lost by warmer water – Heat gained by cooler water

= 3511.2 J – 2131.8 J

= 1379.4J

7. Heat capacity of calorimeter = heat gained by the calorimeter / temperature increases

= 1379.4 J / (35.2 – 25.0) °C

= 135.24 J/°C

B) Heat of Neutralization of HCl-NaOH

1. Temperature of calorimeter and NaOH =25.7 °C

2. ΔT determined from curve after adding HCl to the NaOH =

3. Heat gained by solution = q = msolutionswater Δt

= (100 g)( 4.18 J/g. °C)(31.0 – 25.7) °C

= 2215.4 J

4. Heat gained by calorimeter = q = CcalΔt

= (135.24 J/°C)(31.0 – 25.7) °C

= 716.77 J

5. Total joules released by reaction [(3) + (4)] = 716.77 J + 2215.4 J

= 2932.172 J

6. HCl + NaOH NaCl + H2O

7. The number of moles of HCl in 50 mL of 1.0 M HO = molarity x liters of solution

= 1.0 M x 0.05 L

= 0.05 mol HCl

8. The number of moles of H2O produced in reaction of : 50 mL 1.0 M HCl and 50 mL 1.0 M NaOH

= number of moles of HCl × ratio of moles of H2O to HCl

= 0.05 mol HCl ×(1mol of H2O /1mol of HCl)

= 0.05 mol water

9. Joules released per mole of water formed

= total joules released / number of moles of water produced

= 2932.172 J / 0.05 mol H2O

= 58.64 kJ

C) Heat of Neutralization of HC2H3O2 - NaOH

1. Temperature of calorimeter and NaOH = 27.9 °C

2. ΔT determined from curve after adding HC2H3O2 to the NaOH =

3. Heat gained by solution = q = msolutionswater Δt

= (100 g)( 4.18 J/g. °C)(28.0 – 27.9) °C

= 41.8 J

4. Heat gained by calorimeter = q = CcalΔt

= (135.24 J/°C)(31.0 – 25.7) °C

= 716.77 J

5. Total joules released by reaction [(3) + (4)] = 41.8J + 716.77 J

= 758.57 J

6. HC2H3O2 + NaOH NaC2H3O2 + H20

7. The number of moles of H2O produced in reaction of: 50 mL 1.0 M HC2H3O2 and 50 mL 1.0 M NaOH

= number of moles of HC2H3O2 × ratio of moles of H2O to HC2H3O2

= 0.05 mol HC2H3O2 × (1mol H2O/1mol HC2H3O2)

= 0.05 mol H2O

8. Joules released per mole of water formed

= total joules released / number of moles of water produced

= 758.17 J / 0.05 mol H2O

= 15.17 kJ

DISCUSSIONS

The basic principle of heat transfer applied to obtain the calorimeter heat capacity and

heat of neutralization is when heat is evolved, the reaction is exothermic. If heat is absorbed, the

reaction is endothermic. In this experiment, two exothermic reactions will be observed, and the

heat of reaction for each will be found. The basic principle for the “heat of neutralization,” which

is the enthalpy change produced when an acid and a base react to form water.

The first three readings temperature were recorded for every 5 seconds because in order

to detect if there are small change of temperature as the solution does not mix well yet. This time

was used to wait for the solution to well mixed and reach their equilibrium temperature. At this

time, the transfer of heat is in action. It is also to get the average temperature of the calorimeter.

This average temperature reading would portray the stable equilibrium reading of the

calorimeter.

The value obtain are experimental data that must be compared to the true value in order

to gauge the accuracy of this experiment. The theoretical value of the joules released per mole of

water for the HCl reaction is 58.2 kJ/mol while for acetic acid is 55.8 kJ/mol.

When the magnitude of heat of neutralization for weak and strong acid is compared the

number of moles of NaOH acting on acid in both experiment are same. While initial any final

temperature may vary, the change in temperatures should be the same. Thus, the two heat of

neutralization should be the same.

A few suggestions appropriate apparatus should be used in order to get more accurate

result is a pipet should have been used for maximum accuracy because using a graduated

cylinder leaves room for a crucial error in volume determination, which would then lead to errors

in determination of mass, molar content of the solution, and every other derivative formula.

Inaddition, the thermometer had to be calibrated, which improves accuracy but is itself an

imprecise technique. The thermometer and the calorimeter should wipe till it completely dry to

prevent the errors in reading. The calorimeter also should run in closed area to prevent the heat

easily lost to the surrounding.

CONCLUSION

For experiment part A, temperature of calorimeter and water before mixing is 25.0 °C

while the temperature of warm water is 50.0 °C. We can conclude that heat lost by warmer

water is 3511.2 J. Besides that, heat gained by cooler water 2131.8. J. Therefore, heat

capacity of calorimeter is equal to heat gained by the calorimeter / temperature increases and

the answer is 135.24 J/°C.

For experiment part B, we calculated heat of neutralization of HCI-NaOH. At first,

temperature of calorimeter and NaOH is 25.7 °C. While we can see that ΔT determined from

curve after adding HCl to the NaOH is .Heat gained by calorimeter is 716.77 J. Heat gained

by the calorimeter for heat neutralization of HCI – NaOH is1379.4J.

For experiment part C, we can conclude that there are slightly different in heat gained by

calorimeter of strong acid of HCI and weak acid, HC2H3O2. The heat gained by calorimeter of

weak acid is low than heat gained by calorimeter of strong acid that is 18.52 kJ.

At the end,we can say that the experiment was successful as the procedure was carried

out correctly. The calorimeter prove as a good heat insulator for this experiment, as it prevent the

heat lose as the solution is put in it. Even the result is not too accurate, we can conclude that

neutralization process releases energy in the form of heat and it is exorthermic processes.

Moreover, accurate apparatus can lead to a improvement in the result we got.

REFERENCES

Raymond,C. Chemistry Tenth Edition. (2010). McGraw.Hill International Edition.

Chemical Engineering Faculty. (2010). Chemistry Laboratory CHE 235.

Yeap Tok Kheng. Chemistry. (2008). Pearson Longman.

Universiti Teknologi Malaysia Institutional Repository. (2008). Specific heat capacity of pure

triglycerides by differential scanning calorimeter 2008. Retrieved from

http://eprints.utm.my/5212/

Virtual Chemistry Experiment Calorimetry. (2009). Heat of Neutralization. Retrieved from

http://www.chm.davidson.edu/vce/calorimetry/HeatOFNeutralization.html

Slowinski, E.J.; Wolsey, W.C.; Masterton, W.L. Chemical Principles in the

Laboratory, 7th ed.; Harcourt: Fort Worth, 2001; pp 99-106.