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Edexcel Jun 2009 Paper 3 Q2
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![PMT 2 The enthalpy change for the reaction between zinc and copper(II) sulfate solution was determined using the procedure below. The ionic equation for the reaction is Zn(s) + Cu2+(aq)Zn2+(aq) + Cu(s) Procedure 1. Weigh about 5 g of zinc powder. 2. Measure 50.0 cm3 of 1.00 mol dm3 copper(II) sulfate solution into a polystyrene cup. 3. Stir the solution continuously with a thermometer and measure the temperature of the solution each minute for 3 minutes. 4. At exactly 3.5 minutes add the zinc powder to the copper(II) sulfate solution. 5. Continue to stir the solution and read the temperature each minute from 4 to 10 minutes. The results obtained are shown in the graph below. (a) (i) Use the graph to estimate the maximum temperature change, T, for the reaction. Show your working on the graph. (2) T =C *N34473A0416*<br />
PMT (ii) Calculate the number of moles of copper(II) sulfate in 50.0 cm3 of 1.00 mol dm3 solution. (1) (iii) The 5 g of zinc powder used is an excess. Calculate the mass of zinc that reacts exactly with 50.0 cm3 of 1.00 mol dm3 copper(II) sulfate solution. (1) (1) (iv) Explain why the mass of zinc is not used in the calculation of the heat energy for the reaction.(v) Use the value you have obtained for T to calculate the heat energy produced in the reaction between zinc and copper(II) sulfate. Include units with your answer. Use the expression energy produced (J) = mass of solutionspecific heat capacity of solution temperature rise [Assume the specific heat capacity of the solution to be 4.18 J g1 density of the solution to be 1.00 g cm3.] C1 and the (2) *N34473A0516* Turn over<br />
PMT (vi) Calculate the enthalpy change, H, for this reaction. Your answer should be in units of kJ mol1, expressed to two significant figures and include a sign. (2) H =kJ mol1 (b) (i) Explain why the temperature of the solution is measured for 3 minutes before adding the zinc. (1)(ii) Explain why the temperature of the solution is measured over a period of time after adding the zinc. (1)(iii) A polystyrene cup is used, rather than a glass beaker, to reduce heat loss. Explain why a polystyrene cup is a good choice. (1)*N34473A0616*<br />
PMT (iv) Explain why the solutions are continuously stirred in this experiment. (1)(v) Suggest a piece of apparatus suitable for measuring the 50.0 cm3 of copper(II) sulfate solution in this experiment. (1)(vi) Suggest ONE change in the apparatus used (other than using more accurate measuring equipment) that would improve the accuracy of the results. (1)(c) In two further experiments, using more accurate equipment and an improved method, the H for the reaction between zinc and copper(II) sulfate was determined to be 216.8 kJ mol1 while that for the reaction between zinc and lead(II) nitrate was found to be 154.0 kJ mol1. Place the three metals (copper, lead and zinc) in order of decreasing reactivity and justify your answer by using these H values. (2)(Total for Question 2 = 17 marks) *N34473A0716* Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJune_2009_QP_-_Unit_3_Edexcel_Chemistry_A-level_2-0.jpg)
![Correct Answer Reject Observation: Brown or red-brown or orange (1) Inference: Bromine / Br2 (1) Red Bromide (for bromine) Correct Answer From: Orange or yellow To: blue or green or blue-green Correct Answer Reject Reject Mark two points independently (Hydrogen) bromide oxidized / bromine oxidation number increased (from 1 to 0) / changes from -1 to 0 /Bromide loses an electron / (hydrogen) bromide is a reducing agent (1) sulfuric acid reduced / sulfur oxidation number decreases (from (+)6 to (+)4) / changes from (+)6 to (+)4 / sulfate gains electrons / sulfuric acid is an oxidizing agent (1) Accept (+)VI to (+)IV sulfate reduced Correct Answer Reject Vertical line at 3.5 minutes intersects extrapolated top line (1) Horizontal extrapolated lower line and 66-69 minus 20-22 = (cid:1)T (1) incorrect or no extrapolation line joining points at 3 & 4 minutes & extrapolated to intersect top line (0) Correct Answer (1 x 50 x 103) = 0.0500 IGNORE sf Correct Answer Reject Reject 65.4 x 0.05 = 3.27 (g) / 3.3 (g) Accept 65 x 0.05 = 3.25 (g) / 3.3 (g) Mark Mark Mark Mark Mark Mark Question Number 1 (b)(iii) Question Number 1 (b)(iv) Question Number 1 (b)(v) Question Number 2 (a)(i) Question Number 2 (a)(ii) Question Number 2 (a)(iii)<br />
Question Number 2 (a)(iv) Question Number 2 (a)(v) Question Number 2 (a)(vi) Question Number 2 (b)(i) Question Number 2 (b)(ii) Mark Mark Mark Correct Answer Reject Heat capacity negligible Accept: low specific heat capacity or zinc absorbs less heat than solution Mass negligible No heat absorbed by zinc All heat absorbed by solution Correct Answer Reject 50 x 4.18 x (cid:1)T (1) ((cid:1)T CQ on (a)(i)) Penalise use of incorrect mass here only. IGNORE c = 4.2 Jg11 (cid:1)T 44 45 46 47 48 49 Heat energy (kJ) 9.20 9.41 9.61 9.82 10.0(3) 10.2(4) (units if given must be consistent) (1) IGNORE sf except 1 sf Correct Answer =answer to (a)(v)answer to (a)(ii) (1) For 0.05 mol: Reject (cid:1)T 44 45 46 47 48 49 Heat energy (kJ) 9.20 9.41 9.61 9.82 10.0(3) 10.2(4) (cid:1)H / kJ mol-1 -180 -190 -190 -200 -200 -200 CQ on moles from 2 (a)(ii) Sign and 2 sf (1) [this mark may be awarded for any calculated value] Correct Answer Reject Mark Ensure equilibration or steady temperature or same temperature (as surroundings) More accurate temperature Correct Answer Reject To allow for cooling / a cooling correction / to compensate for heat loss Temperature correction To determine maximum temperature change More accurate temperature /(cid:1)T Mark<br />
Correct Answer Reject Mark Low specific heat capacity Low heat capacity Good insulator Poor heat conductor Low mass Absorbs less heat Correct Answer Ensure uniform temperature Accept to spread out heat (uniformly) IGNORE references to mixing reagents, increasing reaction rate, enabling reactants to react and temperature accuracy. Reject Mark Mark Mark Mark Correct Answer Reject Burette / pipette / measuring cylinder /volumetric or graduated flask Beaker /conical flask Correct Answer Reject Lid on polystyrene cup/ Increase insulation Accept Put cup in a beaker Magnetic stirrer Correct Answer Reject Zn>Pb>Cu OR Zinc displaces both so is most reactive (1) The more exothermic / negative (accept the larger) the (cid:1)H the greater the difference in reactivity (so lead more reactive than copper) (1) If the order of reactivity is reversed maximum 1 Answers in just terms of reactivity or electrochemical series Generalised answers References to energy or enthalpy required for the reaction Question Number 2 (b)(iii) Question Number 2 (b)(iv) Question Number 2 (b)(v) Question Number 2 (b)(vi) Question Number 2 (c)<br />](https://learnah.org/wp-content/uploads/2018/08/June_2009_MS_-_Unit_3_Edexcel_Chemistry_A-level_2-0.jpg)
