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Activity 3 – Lab work

LAB 2: HEAT OF NEUTRALIZATION

Learning outcome

1. To determine heat capacity of a calorimeter.

2. To measure the energy changes accompanying neutralization for weak and strong acids.

3. Demonstrate effective team role and responsibility in the task execution.

Scenario

You are working as a Product Engineer in Berjaya Sdn. Bhd. which produces Alk X. Alk X is a strong base material that used to neutralize accidentally acids spill through acid-base neutralization reaction. Reactions Alk X with acids will generate some heat. As a product engineer, you and your team are asked to construct a simple coffee cup calorimeter and measure the heat changes accompanying neutralization for weak and strong acids with Alk X. Refer to the theory given.

Objectives

This activity requires your team to construct the calorimeter, determine heat capacity of a calorimeter and measure the heat changes accompanying neutralization for weak and strong acids with base. You are provided with a diagram of simple calorimeter (Figure 1).

Assessment

Upon completion of the experiment, write a technical report about your team’s finding. You need to use the following guiding questions as your discussion in the report.

Questions:

1. What is the basic principle of heat transfer applied to obtain the calorimeter heat

capacity and heat of neutralization?

2. Compare the magnitude of heat of neutralization for Part A and B with the theoretical

value.

3. Compare the magnitude of heat of neutralization for weak and strong acid.

4. What is the objective of recording the first 3 readings temperature for every 5

seconds?

5. Suggest appropriate apparatus should be used in order to get more accurate result.

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Pre-Experiment Assessment

A. Planning/Preparation)

All team members arrive at the process operation site to discuss on the plan to construct the calorimeter and measure the energy changes for the heat neutralization reaction.

Task

1. Familiarize with the diagram of calorimeter and all the chemicals needed to run the

experiment.With reference to Figure 1, identify the apparatus needed to construct the

calorimeter.

Figure 1 A simple calorimeter.

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.

Chemicals

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

2. Understand how the calorimeter works to measure the heat changes of neutralization reaction.

3. Decide on the test parameter (temperature of reaction system)

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B. Allocation of Roles and Teamwork

1. Analyze the tasks to be performed and divide among your team who to perform the tasks.

Every student need to fill in the Peer Evaluation Grid form.

No Task description Member

1 Introduction and theory

2 Collecting Data

3 Analyze the result

4 Safety awareness

C. Experimental Procedure

Part A: Heat Capacity of Calorimeter

1. Construct a calorimeter similar to the one shown in Figure 1 by nesting two styrofoam

cups together.

2. Place a thermometer into the hole in the cardboard square and stabilize it by a split

one-hole rubber stopper.

3. Place exactly 50.0 mL of tap water in the calorimeter cup. Allow the system for 10

minutes to reach thermal equilibrium. Record the temperature (to nearest 0.1°C).

4. Place exactly 50.0 mL of hot tap water in a 250-mL beaker. Heat the water until the

temperature is about 15°C – 20°C above room temperature.

5. Record the temperature of the hot water.

6. Pour the hot water into the calorimeter.

7. Replace the lid of the calorimeter and stir the water carefully with the thermometer.

8. Record the temperature of the water every 5 seconds for first 3 readings and every 15

seconds for next 2 minutes.

9. Construct a graph of temperature as a function of time.

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Part B: Heat of Neutralization of HCl – NaOH

1. Dry the calorimeter and the thermometer with a towel. Measure 50.0 mL of 1.0 M

NaOH and add it to the calorimeter.

2. Replace the lid of the calorimeter without the thermometer.

3. Measure exactly 50.0 mL of 1.0 M HCl into a dry beaker. Allow it to stand near the

calorimeter for 4 minutes.

4. Record the temperature of the acid.

5. Rinse the thermometer with tap water and wipe till it dry.

6. Record the temperature of the base solution.

7. Add the HCl to the NaOH.

8. Stir the solution carefully and the record temperature every 15 seconds.

9. Construct a graph of temperature as a function of time.

Part C: Heat of Neutralization of HC2H3O2 – NaOH

1. Repeat the procedure in Part B. Use 1 M HC2H3O2 (acetic acid) instead of 1 M HCl.

D. Post-Experiment Assessment

You have completed the task. Carry out a team review on the test result.

Part A: Heat Capacity of Calorimeter

Notation Time, s Temperature, °C (1)

Temperature, °C (2)

Temperature, °C (3)

Temperature, °C (Average)

Tequilibrium

t0

t1

t2

t3

t4

t5

5

t6

t7

t8

t9

t10

t11

Part B: Heat of Neutralization of HCl – NaOH

Notation Time, s Temperature, °C (1)

Temperature, °C (2)

Temperature, °C (3)

Temperature, °C (Average)

Tequilibrium

t0

t1

t2

t3

t4

t5

t6

t7

t8

t9

t10

t11

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Part C: Heat of Neutralization of HC2H3OH – NaOH

Notation Time, s Temperature, °C (1)

Temperature, °C (2)

Temperature, °C (3)

Temperature, °C (Average)

Tequilibrium

t0

t1

t2

t3

t4

t5

t6

t7

t8

t9

t10

t11

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Appendix

Theory

Every chemical change is accompanied by a change in energy, usually in the form of heat. The energy change of a reaction that occurs at constant pressure is termed the heat reaction or the enthalpy change. The symbol ∆H (the symbol ∆ means “change in”) is used to denote the enthalpy change. If heat is evolved, the reaction is exothermic (∆H < 0); and if heat is absorbed, the reaction is endothermic (∆H > 0). In this experiment, the heat (enthalpy) of neutralization will be measured when an acid and a base react to form water. This quantity of heat is measure experimentally by allowing the reaction to take place in a thermally insulated vessel called a calorimeter. The heat liberated in the neutralization will cause an increase in the temperature of the solution and the calorimeter. If the calorimeter were perfect, no heat would be radiated to the laboratory. The concern in this experiment is with the heat of the reaction and because some heat is absorbed by the calorimeter itself, the amount of heat absorbed by the calorimeter must be known. This requires the determination of the heat capacity of the calorimeter. Heat capacity of the calorimeter means the amount of the heat (that is, the number of joules) required to raise the temperature by 1 Kelvin (1°C). In this experiment, the temperature of the calorimeter and its contents is measured before and after the reaction. The change in the enthalpy, ∆H, is equal to the negative product of the temperature change, ∆T, times the heat capacity of the calorimeter and its contents;

∆𝐻 = −∆𝑇(𝐶𝑐𝑎𝑙𝑜𝑟𝑖𝑚𝑒𝑡𝑒𝑟+ 𝐶𝑐𝑜𝑛𝑡𝑒𝑛𝑡𝑠)

Note that the numerical difference on the Celcius scale is the same as the numerical difference on the Kelvin scale where ∆T is the difference between the final and initial temperatures; ∆T = T f – Ti. Because ∆H is negative for an exothermic reaction whereas ∆T is positive, a negative sign is required in the first equation. Energy balance equations for heat transfer involved;

Heat lost by warmer water = (T2 – Tf) x 50 g x 4.18 J/g.K

Heat gained by cooler water = (Tf – T1) x 50 g x 4.18 J/g.K

Heat lost by warmer water - Heat gained by cooler water = Heat gained by the calorimeter

[(T2 – Tf) x 50 g x 4.18 J/K.g] – [(Tf – T1) x 50 g x 4.18 J/K.g] = (Tf – T1) x heat capacity of calorimeter