VJC H2 Chem 2013 Prelim P2 Soln

 VJC 2013 9647/02/PRELIM/13 [Turn over 1 Victoria Junior College 2013 H2 Chemistry Prelim Exam 9647/2 Suggested Answers 1 Planning A student was provided with a spirit burner containing a ‘fuel mixture’ which was prepared by mixing equimolar amounts of hexane and ethanol. The enthalpy change of combustion of this ‘fuel mixture’ is 13.2 kJ per mole of ‘fuel mixture’. He was told to use the enthalpy change of combustion of this ‘fuel mixture’ to find the heat capacity of a metal calorimeter using the apparatus shown below. Heat capacity is defined as the number of joules of heat needed to raise the temperature of the calorimeter by one Kelvin or one degree Celsius. Additional information: Specific capacity of water is 4.2 J cm3 K1 (a) Construct a balanced equation for the complete combustion of the ‘fuel mixture’ with state symbols. C6H14(l) + C2H5OH(l) + 25/2 O2(g)  8CO2(g) + 10H2O(l) [1] (b) Identify two possible sources of error and suggest an improvement to overcome each of them in the experiment. Errors: Heat loss to the surroundings by the calorimeter and water. Loss in amount of fuel mixture due to evaporation of the fuel mixture as ethanol and hexane are volatile liquids. Improvements: Cover and lag the calorimeter with non-flammable insulating material and conduct the experiment in a draught-free room, to minimize heat loss by the calorimeter and water to the surroundings. Cover the spirit burner to minimize rate of evaporation so as to minimize loss of fuel mixture. [3] spirit burner metal calorimeter 1503

 VJC 2013 9647/02/PRELIM/13 [Turn over 2 (c) Write a plan to determine the heat capacity of the metal calorimeter using the apparatus provided. In your plan you should give details of the procedure (number your steps) and provide a table to record the readings to be taken, including the units. 1) Weigh the spirit burner containing the ‘fuel mixture’ 2) Using a measuring cylinder, measure 100 cm 3 of water into the metal calorimeter. 3) Measure the initial temperature of the water using a thermometer. 4) Light the burner and allow it to heat the water in the calorimeter. 5) Monitor the temperature of water using the thermometer, and extinguish the flame when the temperature of the water reaches about 5 oC 6) Measure the final temperature of the water. 7) Cool and reweigh the spirit burner with the remaining ‘fuel mixture’.   Initial temperature of water/ oC T1 Final temperature of water/ oC T2 Initial mass of spirit burner with ‘fuel mixture’ / g M Final mass of spirit burner with remaining ‘fuel mixture’ /g N [5] (d) Outline how you would determine the heat capacity of the metal calorimeter based on the plan that you have written and other information given in this question. Since density of water is 1 g cm-3, mass of the water in the calorimeter = 100 g Let the Heat capacity of the calor