AJC_H2_CHEM_P2_Solutions

©2014AndersonJC/CHEM 1 H2 Chemistry 9647 2014 JC2 Prelim P2 Suggested Solutions 1 (a) (i) The boiling point increases with concentration because the temperature has to be raised in order to increase the lowered vapour pressure to that of the ambient value. [1] (ii)  [1m] straight–line or curve showing a gradual increase.  [1m] line to begin on the y–axis with the value 100C (or 373 K) labelled with units. [there is no ecf here from (i) to (ii)] [2] (b)  [1m] for a diagram which shows some form of heating (not a water bath, but allow oil–bath or heating mantle) of an apparatus (50 cm 3 round–bottomed flask / boiling tube) containing the KCl solution.  [1m] for showing the position of the thermometer bulb is half–immersed in the solution – the full line in the diagram indicates the water level (to allow accurate determination of the temperature of the equilibrium). [2] 100 C boiling point 0 concentration of potassium chloride (not required) saturated

©2014AndersonJC/CHEM 2 (c) Experimental Procedure 1. Weigh accurately about 2 g of solid KC l in a 50 cm 3 round–bottomed flask and record your reading. 2. Using a 50 cm3 burette, add 20 cm 3 of deionised water into the round–bottomed flask. 3. Stopper and shake the flask to dissolve the solid. 4. Add anti–bumping granules (boiling chips) to the solution. 5. Set up the apparatus as shown in (b). 6. Using a heating mantle (or oil–bath), gently heat the flask containing KC l solution, until the temperature remains constant. 7. Record this temperature (i.e. the boiling point). 8. Repeat steps 1 to 7, using 3 g, 4 g, 5 g and 6 g KC l, respectively.  [1m] for general outline of procedure with coherent sequence of steps leading to determination of boiling point (take reading when temperature remains constant).  [2m] for a method, which gives details / a list of the masses / volumes of water to be used along with masses of solid KC l to produce a solution, provided that the total mass / volume of water does not exceed 100 g / 100 cm 3 AND 0.357(same) waterof volume KCl solid of mass max.  or 0.357 waterof volume smallest (same) KCl solid of mass   [1m] if at least five different concentrations of KCl are prepared. (A method based on adding varying volumes of the water to one mass of solute is allowed, e.g. 10 cm3, 15 cm3, 20 cm3, 25 cm3, 30 cm3)  [1m] for safety & reliability considerations: steps 3 and 4 (or in diagram) Calculation of Molality Taking density of water to be 1 g cm–3 Molality = 1.00 x used waterdeionised of volume 1000x74.6 used KCl solid of mass  [1m] for correct general expression to calculate molality. [6] (d) The experiment is limited by the solution becoming saturated. [1]

©2014AndersonJC/CHEM 3 2 (a) Breath alcohol concentration = 2100 1 x 80 mg / 100 cm3 = 0.03809 mg / 100 cm3 breath alcohol concent