NJC H2 CHEM P2 Question Paper Prelim

NJC Preliminary Examination 9647/02/14 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Answer on the Question Paper. Additional Materials: Data Booklet 9647/02 Wednesday 3 Sept 2014 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /16 3 /16 4 /17 5 /11 Total /72 This document consists of 15 printed pages and 1 blank page.

NJC Preliminary Examination 9647/02/14 2 For Examiner’s Use BLANK PAGE

3 NJC Preliminary Examination 9647/02/14 [Turn over For Examiner’s Use Answer all the questions. 1 Planning (P) A student was provided with a spirit burner. He was asked to determine the enthalpy change of combustion under laboratory conditions, H c, for ethanol using the following setup. Knowing that there could be significant heat loss arising from the above experimental setup, he decided to calibrate the calorimeter by burning 0.60 g of methanol (CH 3OH) to determine the calorimeter’s heat capacity, C calorimeter, which accounts for both the water and the copper can. 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. The temperature of the calorimeter rose from 25.0°C to 33.8°C. The same calorimeter was then used to measure the enthalpy of combustion of ethanol. (a) Given the enthalpy change of combustion of methanol is − 715 kJ mol –1, use the information above to calculate the heat capacity of the calorimeter, C calorimeter, stating its units. [2] calorimeter (copper can containing 50 cm3 of water) draught shield wick spirit burner containing selected alcohol stirrer lid thermometer

NJC Preliminary Examination 9647/02/14 4 For Examiner’s Use (b) Given the enthalpy change of combustion of ethanol is approximately −1370 kJ mol–1, calculate the minimum mass of ethanol required to give the same temperature change as that in the calibration. [2] (c) Write a plan to determine the enthalpy change of combustion, H c, of ethanol that the student will carry out. You may assume that you are provided with:  a thermometer with divisions of 0.2 °C division;  the apparatus normally found in a school or college laboratory. Your plan should include details of  the procedure to determine the enthalpy change of combustion of ethanol;  the readings recorded using appropriate table(s), including units;  precautions taken to ensure reliability of the experiment  an outline of how the results would be used to determine the enthalpy change of combustion of ethanol based on the plan that you have written using arbitrary values. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………..…………………….. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………………

5 NJC Preliminary Examination 9647/02/14 [Turn over For Examiner’s Use ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………. [7] (d) Identify one potential safety hazard in this experiment and state how you would minimise this risk. ....................................................................................................................................... ....................................................................................................................................... ...................................................................................................................................[1] [Total: 12]

NJC Preliminary Examination 9647/02/14 6 For Examiner’s Use 2 The simplest chemical reactions are those that occur in the gas phase in a single step, such as the transfer of a chlorine atom from ClNO2 to NO. ClNO2(g) + NO(g) NO 2(g) + ClNO(g) (a) (i) An equimolar mixture of C lNO2(g) and NO(g), at a total initial pressure of 3 atm, was allowed to react in a closed vessel at 1000 K. When equilibrium was attained at the 5 th minute, the partial pressure of C lNO2 was found to be 0.57 atm. Calculate the value for the equilibrium constant, K p , of this system. (ii) At the 10 th minute, more C lNO2 gas was pumped into the vessel at 1000 K, increasing the partial pressure of ClNO2 to 1 atm. Suggest how the position of the equilibrium would change. …………………………………………………………………………………………........... …………………………………………………………………………………………........... …………………………………………………………………………………………........... (iii) Hence illustrate clearly, in the pressure time graph below, the changes in the partial pressures of C lNO2 and NO2 when (I) the above gaseous system first reached equilibrium at the 5 th minute, (II) more C lNO2 gas was added into the vessel at the 10 th minute and a new equilibrium was attained at the 15th minute. Pressure Time 0

7 NJC Preliminary Examination 9647/02/14 [Turn over For Examiner’s Use (iv) Suggest whether the addition of an inert gas into the vessel would affect the position of the equilibrium. …………………………………………………………………………………………........... …………………………………………………………………………………………........... [7] (b) C lNO2 can behave as an ideal gas under certain experimental conditions. (i) State the two assumptions of kinetic theory of ideal gas. …………………………………………………………………………………………........... …………………………………………………………………………………………........... …………………………………………………………………………………………........... (ii) Predict whether C lNO2 behaves ideally under high pressure. …………………………………………………………………………………