Edexcel Jun 2013 Paper 1 Q20 (with explained solutions) |

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Edexcel Jun 2013 Paper 1 Q20

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20 Copper(II) sulfate solution, CuSO4(aq), can be made by adding an excess of solid copper(II) oxide, CuO, to boiling dilute sulfuric acid. This is an exothermic reaction. The balanced equation for this reaction is CuO(s) + H2SO4(aq) o CuSO4(aq) + H2O(l) (a) (i) Complete the ionic equation for this reaction, including state symbols. CuO(s) + (ii) Calculate the mass of copper(II) oxide needed, if a 10% excess is required, when 0.020 mol of sulfuric acid is completely reacted. [Relative atomic masses: Cu = 63.5 and O = 16.0] (b) (i) Suggest, with a reason, how the copper(II) oxide should be added to the boiling sulfuric acid. (2) (2) (2)*P41649A01324* 13 Turn over<br />
(ii) When the reaction is complete, the excess copper(II) oxide is removed by filtration. To prepare crystals of copper(II) sulfate-5-water, CuSO4.5H2O, the resulting solution is boiled to remove excess water. How would you know when sufficient water had been removed? (1)(iii) After cooling the solution, crystals form. State the colour of the crystals. (1)(iv) The crystals all have the same shape. What does this indicate about the arrangement of the ions? (1)(c) (i) Calculate the molar mass of copper(II) sulfate-5-water, CuSO4.5H2O. Remember to include the appropriate units in your answer. You will need to use the Periodic Table as a source of data. (2) 14 *P41649A01424*<br />
(ii) Calculate the percentage yield if 2.7 g of copper(II) sulfate-5-water is obtained from 0.020 mol of sulfuric acid. (iii) What is the most likely reason for the yield being well below 100%? (2) (1)(d) When the crystals are heated, they turn white. On adding water, they return to their original colour. Suggest a use for this reaction. (1)(Total for Question 20 = 15 marks) *P41649A01524* 15 Turn over<br />
BLANK PAGE 16 *P41649A01624*<br />

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Question Number 20(a)(i) CuO(s) + 2H+(aq)Cu2+(aq) + H2O(l) Acceptable Answers Left hand side (1) right hand side (1) Reject Mark If SO4 2- are on both sides max one mark ALLOW correct entities and balancing with no or incorrect state symbols for one mark. Charges within water molecule ALLOW multiples It is sometimes difficult to be sure of the 2 on the Cu2+. Give BOD provided 2H+ on the left of the equation Question Number 20(a)(ii) 1.749/1.75/1.7 with or without Acceptable Answers working scores 2 If answer incorrect look for Mass = 79.5 x 0.02 OR =1.59 (1) OR TE from incorrect mass for one mark Their mass x 1.1= their correct answer to 2/3/4SF (g) (1) Accept crossed 7s ALLOW both ways of writing 4 and be generous if 4 looks like 9 Acceptable Answers Question Number 20(b)(i) Add in small portions / use a spatula / use a small spoon / slowly / gradually (1) To prevent (mixture / acid) boiling over / frothing / spilling / splashing / splash back (1) Mark independently Bubbles are neutral IGNORE add carefully / cautiously alone Reject 1.74 1.8 Mark Reject Mark Spitting / violent reaction / fizzing Because reaction is exothermic alone Bubbles of carbon dioxide<br />
Question Number 20(b)(ii) Dip in glass rod. Remove and allow Acceptable Answers to cool. See if crystals form ALLOW any workable suggestion Examples: See crystals / salt forming around edge of beaker Depth of colour of solution increases Solution / colour becomes darker Solution / colour becomes deeper blue Dark blue solution Reduce volume by at least half / until crystals form Question Number 20(b)(iii) Blue Acceptable Answers Question Number 20(b)(iv) (The ions are arranged in a) Acceptable Answers regular (way) / lattice OR The ions are arranged in the same way / have same arrangement / have uniform arrangement The term structure is neutral and should be ignored IGNORE statements about ions attracting or repelling Mark Reject Solution thickens Precipitate forming Mark Mark Reject Any mention of green or other colour Reject The ions are arranged in a similar / fixed way<br />
Question Number 20(c)(i) Acceptable Answers 249.6 g mol-1 ALLOW 249.5 g mol-1 ALLOW 250 g mol-1 value (1) units (1) Common wrong values are 159.5 / 6, 185.5 / 6, 249 ALLOW unit mark with any or no value. ALLOW g / mol for unit Question Number 20(c)(ii) Max yield = 249.6 x 0.02 = 4.992(g) (1) Acceptable Answers Percentage yield = 2.7 x 100 4.992 = (54.0865) = 54% (1) If 249.5 is used = (54.1082) = 54% OR 2.7 / 249.6 = 0.01082 (1) Percentage yield = 0.01082 x 100/0.02 = 54% (1) ALLOW TE from any value in (i), and note 159.6 gives 84.6% 185.6 gives 72.7% IGNORE SF except one SF Correct answer, no working scores (2) Question Number 20(c)(iii) (Copper(II) sulfate is soluble) so some Acceptable Answers remains in solution / some remains on the filter paper IGNORE other transfer errors Incomplete crystallization / not all the crystals are formed Reject g/mol-1 Reject Mark Mark Mark Reject Experimental error/ incomplete reaction Filtering alone Efflorescence<br />
Acceptable Answers Reject This is a (chemical) test for (the presence of) water Invisible ink Moisture / humidity test Test to see if solutions are aqueous Check to see if substance is hydrated Drying agent Quantitative measurements of water content. Mark Total for Question 20 = 15 Marks Question Number 20(d)<br />

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