Universiti Tunku Abdul Rahman (kampar Campus) Bachelor Of Science (hons)

Universiti Tunku Abdul Rahman (Kampar Campus) Bachelor of Science (Hons) Biotechnology Year 1 Semester 2 Group 1 Laboratory 1B (UESB 1212) (II) The Properties of Matter Lecturer: Ms. Chew Yin Hoon Student’s Name: Cheah Hong Leong Student’s ID: 08AIB03788 Experiment No. 1 Title: Determination of the Enthalpy Change of Reaction of a Monobasic Acid with Sodium Hydroxide. Date: 20 January 2009

Title: Determination of the Enthalpy Change of Reaction of a Monobasic Acid with Sodium Hydroxide. Objective: -

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To determine the calorimeter constant of a given Dewar flask (calorimeter). To determine the enthalpy change of the reaction between nitric acid with sodium hydroxide.

Introduction: Thermodynamic is the study of energy and heat in motion. The enthalpy is the heat content of a material under a state. Usually there are changes in enthalpy of a material when any chemical or physical changes take place. This is due to the chemical bonds formation and deformation that occur during the reaction. When the chemical bonds is formed, energy is released to the environment, while when chemical bonds is breaked, energy is required in order to break the bonds. Therefore, any chemical changes that take place will lead to the changes in enthalpy of the material. In a laboratory, it is hard to measure accurately the transfers of heat in a particular reaction. To measure accurately the transfers of heat in a reaction, the reaction must be occurs in an isolated system from the surrounding environment. In other words, the reaction must be occurs adiabatically so that no heat, or at least minimum of heat can transfers to and from the surrounding environment. The isolated system can be provided by the calorimeter. Calorimeter is an apparatus used to measure the heat change (enthalpy change). There are many kinds of calorimeters; one of the commonly used in a laboratory is the Dewar flask. Dewar flask is thermos bottle apparatus. Dewar flask has an insulating vacuum space that does not allow any exchange of heat of the content in it with the surrounding environment. Therefore, all the content in it will remain in constant temperature, any change in temperature must be due to chemical reaction takes place in it. Every calorimeter has a unique calorimeter constant. Calorimeter constant of the particular calorimeter must be determined first before the apparatus is used to calculate the enthalpy of a reaction occurs in it. The calorimeter constant can be determined by first measure the changes in temperature when a reaction of a known enthalpy, occurs in it. Then, the calorimeter constant can be calculated by the following formula: Ccal = ∆H ∆T

Experimental Procedures: Apparatus and Materials-

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Dewar flask Stop clock Thermometer 25 cm3 graduated pipette Suction bulb 10 cm3 graduated cylinder Burette Retort stand Beakers Concentrated sulphuric acid ( H2SO4 ) Concentrated nitric acid ( HNO3 ) 1M of sodium hydroxide 0.1 M of hydrochloric acid ( HCl ) Methyl orange indicator

ProcedurePart 1: Determination of calorimeter constant of the given Dewar flask 1. 100 cm3 of distilled water was pipetted into the Dewar flask (calorimeter).

2. The water in the flask was stirred with the thermometer. 3. Meanwhile, the temperature of the water was measured and recorded at interval of 1 minute over a period of 5 minutes. 4. About 2 cm3 of concentrated sulphuric acid was introduced into the calorimeter by a graduated cylinder at the end of the period. 5. The solution in the calorimeter was continually stirred; the temperature was continually measured and recorded at 1 minute interval over the period of 10 minutes until the temperature value had become constant. 6. The solution in the calorimeter was allowed to cool. 7. A burette was filled in with 1M of sodium hydroxide solution and clamp onto a retort stand. 8. 25 cm3 of the sulphuric acid solution in the calorimeter was pipetted into a beaker. 9. The sulphuric acid solution was titrated against the 1M of sodium hydroxide solution so that the molarity of the sulphuric acid can be determined.

Part 2: Determination of the enthalpy of reaction between nitric acid and sodium Hydroxide. 1. The calorimeter of known constant was introduced with a mixture of 50 cm3 of

2. 3.

4. 5.

sodium hydroxide solution and 50 cm3 of water. The solution in the calorimeter was stirred and the temperature observation was made at interval of 1 minute over a period of 5 minutes. The temperature value obtained was recorded. After the period of time, the solution in the calorimeter was added with 5cm3 of 10M nitric acid solution from a graduated pipette. The solution in the calorimeter was continually stirred and the temperature of the solution was continually measured and recorded at interval of 1 minute over a period of 10 minutes. At the end of the period of time, the solution was added with 3 drops of methyl orange indicator to ensure the acidity of the solution. If the solution was found to be alkaline, it must be titrated with 0.1M of hydrochloric acid, and vice versa.

Part 3: Determination of the enthalpy of dilution of nitric acid 1. 100 cm3 of distilled water was pipetted into the calorimeter by graduated pipette.

2. The distilled water was stirred with thermometer and the temperature of water was measured and recorded at interval of 1 minute over the period of 5 minutes. 3. At the end of the period of time, nitric acid was introduced into the distilled water in the calorimeter. 4. The solution in the calorimeter was continually stirred and the temperature was continually recorded at interval of 1 minute over the period of 10 minutes.

Experimental results: DataTable 1: Temperature records of the water and sulphuric acid solution in the calorimeter. Time, t (min) 1 o Temperature, T ( C) 2 6.0 11 3 2.5

12 3 2.5

13 3 2.5

14 3 2.5

2 2 6.0 15 32.5

3 2 6.0

4 2 6.0

5 2 6.0

6 3 3.0

7 3 2.5

8 3 2.5

9 3 2.5

10 32.5

Table 2: Volume of sodium hydroxide solution required in titration with sulphuric acid solution Burette readings, V (cm3) 22.2 1.1 21.1

Final volume reading Initial volume reading Volume of NaOH solution

Table 3: Temperature records of sodium hydroxide solution before and after the addition of nitric acid in calorimeter. Time, t (min) 1 Temperature, T (oC) 2 5.0 11 3 0.5

12 3 0.5

13 3 0.5

14 3 0.5

2 2 5.0

3 2 5.0

4 2 5.0

5 2 5.0

6 3 0.5

7 3 0.5

8 3 0.5

9 3 0.5

10 30.5

15 30.5

Observation on the colour of the solution in the calorimeter after the addition of nitric acid on the sodium hydroxide solution: red colour appears after drops of methyl orange indicator was added into the solution. Table 4: Temperature records water and nitric acid solution in the calorimeter. Time, t (min) 1 Temperature, T (oC) 2 6.0 11 2 6.5

12 2 6.5

13 2 6.5

14 2 6.5

2 2 6.0 15 26.5

3 2 6.0

4 2 6.5

5 2 6.5

6 2 6.5

7 2 6.5

8 2 6.5

9 2 6.5

10 26.5

Analysis and CalculationsFrom graph 1, The change in temperature, ∆T = 6.5 oC From table 2, 21.1 cm3 of 1M sodium hydroxide solution required to titrate the 25.0 cm3 of sulphuric acid solution 1 mole of sodium hydroxide produces 1 mole of hydroxide ions when dissolved in water. Number of moles of NaOH required in the titration = MV 1000 = (21.1 cm3)(1M) 1000 = 0.0211 mole Number of moles of hydroxide ions = 0.0211 mole 1 mole of sulphuric acid produces 2 moles of hydroxonium ions when dissolved in water. 1 mole of hydroxonium ions reacts with 1 mole of hydroxide ions; therefore, 0.0211 moles of hydroxonium ions react with 0.0211 moles of hydroxide ions. Number of moles of hydroxonium ions = 0.0211 mole Number of moles of sulphuric acid = 0.0211 mole 2 = 0.01055 mole MV = 0.01055 mole 1000 (25.0 cm3)(M) = 0.01055 mole 1000 Number of moles of sulphuric acid = 0.422M

By plotting the graph of heat liberated against molarity of sulphuric solution, the enthalpy of reaction can be determined from the graph obtained. From graph 2, ∆H = 3.016 KJ Ccal = ∆H ∆T = 3.016 KJ 6.5 oC = 0.464 KJ/ oC From graph 3, The change of temperature, ∆T = 5.5 oC ∆H = Ccal. ∆T = (0.464 KJ/ oC) (5.5 oC) = 2.552 KJ However, the enthalpy obtained from the calculation above is still incorrect; the enthalpy of dilution of nitric acid must be considered. From graph 4, The change of temperature, ∆T = 0.5 oC ∆Hdilution = Ccal. ∆T = (0.464 KJ/ oC) (0.5 oC) = 0.232 KJ Given that ∆Hreaction = ∆H - ∆Hdilution = 2.552 KJ – 0.232 KJ = 2.320 KJ

= -2.320 KJ Discussion: Dewar flask is used as calorimeter because of its thermos flask properties. It has a layer of vacuum that do not allows any transfer of heat. Therefore, any changes of temperature due to chemical changes can be measured accurately. However, in this experiment, the temperature change of the contents was not measured accurately because the Dewar flask was opened when the temperature was measured. In other words, the content in the Dewar flask was not fully isolated and the chemical changes were not taken place adiabatically. Therefore, there were some minor exchanges of heat of the system with the environment. The temperature measured was not fully accurate and therefore the enthalpy of reaction calculated also not fully accurate. The enthalpy of the reaction calculated was only merely accurate. The reaction was known to be exothermic because the temperature increase when the reaction occurred shown that heat was released. In the part 3 of the experimental procedure, the purpose of the procedure was to obtain the enthalpy of dilution of nitric acid in water. The dilution of nitric acid in water also involves the enthalpy change, which also has to be taken account into the calculation. Conclusion: The enthalpy change of the reaction of sodium hydroxide solution with the nitric acid solution, ∆Hreaction is about -2.320 KJ. References: Zvi Szafran, Ronald M. Pike, Judith C. Foster. (2003). Microscale General Chemistry Laboratory With Selected Microscale Experiment, Second Edition. John Wiley & Sons, Inc.