© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Calculating yield Higher tier question Click anywhere on this screen to proceed.

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© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Calculating yield Higher tier question Click anywhere on this screen to proceed. Navigate using the links at the bottom of every screen.

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer Question (part 1) A chemist makes an apple flavouring called pentyl pentanoate in a chemical reaction. The equation for the reaction is given below. (a)Calculate the maximum mass of pentyl pentanoate that can be made from 100 g of pentan-1-ol. The formula mass of pentyl pentanoate is 190 g The formula mass of pentan-1-ol is 88 g [3] C 4 H 9 COOH + C 5 H 11 OH C 4 H 9 COOC 5 H 11 + H 2 O pentanoic acid pentan-1-ol pentyl pentanoate

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer Question (part 2) (b)The chemist wanted to make a banana flavouring, pentyl ethanoate. He calculated that the maximum yield of pentyl ethanoate is 500 g. He did the experiment but made only 250 g of pentyl ethanoate. Calculate the percentage yield of pentyl ethanoate for this experiment. Show clearly how you work out your answer. Percentage yield of pentyl ethanoate = ……………… % [2]

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer Explanation of question This question assesses specification statements on calculating yield. Both (a) and (b) ask you to do calculations. Make sure you show all stages of your working so that the examiner can follow them through. If you make a mistake, the examiner may still be able to award marks for the correct method.

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer D–C answer (a)Pentan-1-ol = 100 ÷ 88 So pentyl pentanoate = 100 ÷ 88 × 190 = 217 g (b)500 ÷ 250 = 2 % comment The answer to (a) is correct and so gains full marks. However, the working is poorly set out. The candidate would have gained no marks if they had made a mistake in their calculations. The answer to (b) is incorrect. The candidate has not used the correct formula for the calculation. In total, this candidate gains three marks. NextPrevious.

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer B–A* answer (a)Number of moles of pental-1-ol = mass there is ÷ mass of one mole = 100 ÷ 88 = 1.14 The equation shows that 1 mole of pentan-1-ol can make a maximum of 1 mole of pentyl pentanoate. So the maximum mass of pentyl pentanoate = number of moles × mass of 1 mole = 1.14 × 190 = g comment The answers to both parts are laid out clearly and well explained. Both answers are correct so the full five marks are gained. There are other methods you can use for working out these calculations. NextPrevious.

© Oxford University Press 2011 Unit C2 Part 1 Upgrade: Model answers 8 Question Explanation of question Answer B–A* answer (continued) (b)Percent yield = (mass made ÷ max mass possible) × 100% = (250 ÷ 500) × 100% = 50% comment The answers to both parts are laid out clearly and well explained. Both answers are correct so the full five marks are gained. There are other methods you can use for working out these calculations. NextPrevious.