AJC H2 CHEM P2

AJC JC2 PRELIM 2014 9647/02/H2 [Turn over ANDERSON JUNIOR COLLEGE 2014 JC2 PRELIMINARY EXAMINATIONS     NAME:______________________________ PDG:_____ /13 Register No: _____   CHEMISTRY 9647/02 Higher 2 3 September 2014 Paper 2 Structured Questions 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, PDG and register number on all the work you hand in. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all the questions. The use of an approved scientific calculator is expected where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 2 1 Total / 72 2 3 4 5 This document consists of 24 printed pages and 1 blank page.

2 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  1 Planning (P) At any temperature, equilibrium can be established between a liquid X and the vapour given off by that liquid. The pressure exerted by the vapour in equilibrium with the liquid is known as the vapour pressure. X(l) X(g) As the temperature of the system is raised, the vapour pressure increases. When this vapour pressure becomes equal to the surrounding (ambient) air pressure, the liquid boils. When the liquid contains a dissolved solid (solute), the vapour pressure above the liquid is reduced. To investigate how the boiling point of an aqueous solution of potassium chloride changes with concentration, a series of known, but different, concentrations of potassium chloride is prepared. Each solution is heated and its boiling point is determined. A graph of boiling point against concentration is then plotted. (a) (i) By considering how the vapour pressure changes as the concentration of aqueous potassium chloride increases, predict and explain how the boiling point of the solution will be affected by the concentration of the solution. …………………………………………………………… ………………………………………....... …………………………………………………………… ………………………………………....... …………………………………………………………… ………………………………………....... (ii) Display your prediction in the form of a sketch graph, labelling clearly the point representing the boiling point of pure water and its value, stating the units. [3] boiling point 0 concentration of potassium chloride

3 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  (b) Draw a diagram of the assembled apparatus you would use in the experiment. You should use only the apparatus normally found in a school or college laboratory and show clearly (i) how the solution will be heated and over–heating of the solution prevented; (ii) how the thermometer will be positioned. Label each piece of apparatus used, indicating its size or capacity, where appropriate. [2]

4 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  (c) When investigating how the boiling point of a solution changes with concentration, it is more convenient to represent the concentration of a solution as a molality. The molality of a solution is defined as the number of moles of a solute dissolved in one kilogram of water. Using the information given above, you are required to write a plan to investigate how the boiling point of an aqueous solution of potassium chloride changes with concentration of the solution. In addition to the standard apparatus found in a laboratory, you may assume that you are provided with:  100 g of deionised water (you should take particular note of this limited supply of water);  solid potassium chloride, KC l. [solubility of KCl at 25 C = 35.7 g per 100 g water] Your plan should include details of:  the preparation of a series of solutions of potassium chloride that can be used in the apparatus you have shown in (b) to obtain sufficient data to plot a graph as in (a)(ii);  how you would calculate the molality of one of these solutions. [A r: K, 39.1; Cl, 35.5; density of water = 1.00 g cm–3] …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………...............

5 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... [6] (d) State a limiting factor that must be taken into account when increasing the concentration of the aqueous potassium chloride. …………………………………………………… ………………………………………………............... …………………………………………………… ………………………………………………............... [1] [Total: 12]

6 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  BLANK PAGE

7 AJC JC2 PRELIM 2014 9647/02/H2 [Turn over  2 Blood alcohol concentration (BAC) is a good measure of the extent to which the activity of the central nervous system is depressed. It is usually defined as follows: BAC = mg of ethanol per 100 cm3 of blood At present in Singapore, the legal limit to drive is 80 mg of ethanol per 100 cm 3 of blood. If the blood of the driver is found to exceed this legal limit, he will be charged with drink–driving. Ethanol is sufficiently volatile to pass from the blood into the air in the lungs and the following equilibrium is set up. C2H5OH (blood) C2H5OH (g) As the ethanol concentration in the breath is related to that in the blood, a traffic police officer can test the driver’s breath using a device called a breathalyz er instead of drawing a driver’s blood to test his ethanol le