CIE Nov 2013 v3 Paper 5 Q2 (with explained solutions) |

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CIE Nov 2013 v3 Paper 5 Q2

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Examiners For Use When heated, aqueous hydrogen peroxide, H2O2, decomposes to form oxygen and water. 2H2O2(aq)2H2O(l) + O2(g) The decomposition can also occur at room temperature if a suitable catalyst is added. Both of the solids, manganese(IV) oxide and lead(IV) oxide, will catalyse the decomposition. The following information gives some of the hazards associated with manganese(IV) oxide and lead(IV) oxide. Manganese(IV) oxide: Poisoning can occur by inhalation or swallowing the powder. Lead(IV) oxide: Poisoning can occur by inhalation or swallowing the powder. The powder can also cause skin irritation. You are provided with a 0.300 mol dm3 solution of hydrogen peroxide and a syringe with a capacity of 100 cm3. (a) Provide the following information about experiments you would carry out to collect oxygen from the decomposition of hydrogen peroxide and to determine, using identical masses, which of the two catalysts was the most ef cient at promoting this decomposition: a fully labelled diagram of the apparatus to be used that would ensure that no oxygen would be lost when the experiment was carried out, a calculation of the maximum volume in cm3 of the aqueous hydrogen peroxide that could be used such that the oxygen produced would not exceed the volume of the syringe, a statement of the measurements you would take that would allow you to say which of the catalysts was most efficient. The molar volume of a gas at 25 C is 24.0 dm3. Please continue into the space provided on the next page if necessary.UCLES 2013 9701/53/O/N/13 [Turn over<br />
Examiners For Use [6] (b) What other feature of the catalyst should be controlled?[1] (c) If one of the experiments takes 2 minutes to complete, draw a sketch graph with labelled axes showing how the volume of oxygen produced will vary with time between 0 and 3 minutes.UCLES 2013 9701/53/O/N/13 [2]<br />
(d) State the hazards that might be encountered when using the solids required in this experiment and give the one essential precaution you would take to make sure these chemicals were handled safely during the experiments.[1] [Total: 10] Examiners For UseUCLES 2013 9701/53/O/N/13 [Turn over<br />

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$PMT Page 2 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 53 Question Expected Answer Mark (a) (i) (The solubility of air) decreases (as the temperature is increased). Dissolving is exothermic so an increase in temperature will promote the reverse reaction (or backwards or right to left). (ii) Axes are labelled AND graph is a curve/straight line showing a decrease in solubility with temperature. Graph is scaled and starts at 0 o point (25 o C, 19 cm dm 3 C on the solubility axis AND goes through ), AND ends at point (100 o 3 dm ) AND C, 0cm provided there is no maximum or minimum in the curve. Units required for this mark. (b) (i) temperature (ii) solubility (of air). Total 5 (a) Diagram shows a container with both chemicals named and attached to a syringe connected without leaks. Container shows the catalyst and hydrogen peroxide separated ready to mix. 100 cm of oxygen is 100/24000 = 0.00417 (mol) (0.004166666) Mol of H2O2 is 2mole answer above = 0.00834 (0.00833333) (ecf on alternative volume of oxygen used) Volume of hydrogen peroxide is therefore (answer above1000)/0.30 (27.8 cm Allow 28 cm ) (27.78 cm ) (27.7777773 cm (units are required) (reverse calculation also accepted) The reaction is timed from the moment of mixing to the collection of a stated volume of oxygen. (b) surface area of catalyst. (c) Axes are labelled (vol and time or min or s etc.) AND graph is a curve starting at the origin, shows the steepest slope at the start and slowing down as reaction proceeds x-axis has numerical scale from the origin to at least 3 min and graph shows no change in volume of oxygen after 2 minutes. The time axis must be scaled and have a unit of min or s.Cambridge International Examinations 2013<br /> PMT Page 3 Mark Scheme Syllabus Paper GCE A LEVELOctober/November 2013 9701 53 Question Expected Answer Mark (d) lead(IV) oxide causes (skin) irritation AND wear (safety) gloves OR Either catalyst or both catalysts (or names or powders or solids) are poisonous AND wear a face mask OR do in a fume cupboard. Total 10 (a) Mr(CCl 4) = 154 AND Mr(C2H2Cl 4) = 168 (b) (i) Mol of CCl 4 = 0.0469 AND mol of C2H2Cl 4 = 0.0531 AND mole fraction = 0.0469/(0.0469 + 0.0531) = 0.469 (ii) Mol of CCl 4 = 0.0918 AND mol of C2H2Cl 4 = 0.00821 AND mole fraction = 0.0918/(0.0918 + 0.00821) = 0.918 (c) The x-axis must start at zero and be labelled as mole fraction with no units and y-axis as temperature or T/ C. Plotted points must cover at least half the grid in both directions. All 16 points plotted correctly The vapour line is a continuous curve of best fit that does not deviate to accommodate an off curve point. The liquid line is a continuous curve of best fit that does not deviate to accommodate an off curve point. (d) Anomalous point is circled at T = 99.3 o C (for the vapour curve). Analysis was made at a temperature that was too low. (e) Horizontal line drawn from 0.500 on the liquid mol fraction curve to meet vapour curve. Correctly reads the value from the vapour curve (f) For C2H2Cl 4 (0.5/120)100 = 0.417% OR (1.0/120)100 = 0.833% For CCl 4 (0.5/76)100 = 0.658% OR (1.0/76)100 = 1.316% (g) (i) CCl (ii) Vapour produced when a mixture is heated has a greater proportion of CCl4 than the mixture/liquid. Total 15Cambridge International Examinations 2013<br />$

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