AQA A-level CHEMISTRY (7405/3) Paper 3 Mark scheme June 2023

AQA A-level CHEMISTRY (7405/3) Paper 3 Mark scheme June 2023. catalyst ALLOW reduces Ea IGNORE speeds up reaction IGNORE provides alternative path IGNORE proton donor IGNORE dehydrating agent 1 Question Answers Additional comments/Guidelines Mark 1.2 electric heater/heat mantle or (hot) water bath IGNORE not with a Bunsen/naked flame / gently ALLOW hot water ALLOW heating/hot plate/ sand bath / oil bath ALLOW reference to flame/Bunsen if in context of heating a water bath NOT any indication of direct heat from Bunsen 1 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 12 Question Answers Additional comments/Guidelines Mark 1.3 M1 there is a bung/stopper (in the end of the condenser) M2 idea of pressure build up M3 water goes the wrong way through the condenser M4 water does not fill the condenser / condenser is not cool enough owtte M2 stopper could be forced out IGNORE glass shatters / explodes water in at top / out at bottom IGNORE condenser is wrong way round ALLOW less condensing / vapour/gas/reactants/products will not condense / not as effective at cooling/condensing vapour/reactants/products escapes IGNORE uneven cooling NOT mixture in flask not cooled ALLOW M1/M3 neck of flask not sealed owtte M2/M4 vapour/reactants/products can escape IGNORE references to clamps 4 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 13 Question Answers Additional comments/Guidelines Mark 1.4 M1 to neutralise/react with/remove the acid M2 carbon dioxide / gas is produced ALLOW carboxylic/ethanoic and/or sulfuric IGNORE react with/neutralise the distillate/mixture IGNORE to act as a base NOT if incorrect acid named ALLOW effervescence / bubbles / fizzes IGNORE water vapour produced NOT if incorrect gas named IGNORE pressure build up (as in Q) 2 Question Answers Additional comments/Guidelines Mark 1.5 M1 ethyl ethanoate/it is immiscible with / insoluble in water M2 ethyl ethanoate/it is less dense / has lower density (than water) ALLOW water/solution and ethyl ethanoate/it do not mix, OR aqueous and organic layers do not mix ALLOW ethyl ethanoate/it is hydrophobic IGNORE references to polarity / intermolecular forces IGNORE different/low density NOT lighter ALLOW answers for either mark from either part 2 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 14 Question Answers Additional comments/Guidelines Mark 1.6 to remove/absorb water / as a drying agent ALLOW reacts with water ALLOW to dry the product/it IGNORE dehydrates NOT reference to crystals forming NOT to dry the reactants NOT to remove soluble impurities 1 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 15 Question Answers Additional comments/Guidelines Mark 1.7 M1 mass of ethanol = 10 x 0.790 (= 7.90 g) M2 amount of ethanol = 7.90 46.0 (= 0.172 mol) AND amount of ethanoic acid = 5.25 60.0 (= 0.0875 mol) M3 (limiting reagent is) ethanoic acid M4 (max amount of ethyl ethanoate = 0.0875 mol) max mass of ethyl ethanoate = 88.0 x 0.0875 (= 7.70 g) M5 % yield = 5.47 M4 x 100 = 71.0% (70.6 to 71.1 to min 2sf) Allow ECF at each stage M1 scores from 0.172 mol of ethanol M2 need to see numbers or sums for both substances M2 10/46 can only be ECF if 10 is identified as a mass M3 ECF from M2 if both amounts clearly shown and nethanol<nethanoic acid M4 independent of M3 Alternative M4 & 5 M4 Amount of ethyl ethanoate formed = 5.47 88.0 (=0.0622) M5 % yield = M4 0.0875 x 100 = 71.0% Correct answer scores M4 and M5 but mark M1/2/3 separately M5 must show an attempt at mass or moles of ester formed divided by mass or moles of ester expected 5 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 16 Question Answers Additional comments/Guidelines Mark 1.8 reaction is an equilibrium/reversible ALLOW losses during distillation/isolation/purification/transfer / incomplete distillation / side reactions / byproducts ALLOW incomplete reaction ALLOW impurities/contamination/water present / not dry IGNORE water is also produced (during the reaction) 1 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2023 17 Question Answers Additional comments/Guidelines Mark 2.1 Displayed formula of pentan-1-ol NOT pentan-3-ol NOT –OH