AQA_A Level Chemistry Paper 3_Mark Scheme 2022 | Practice Paper 3
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AQA A Level Chemistry Paper 3 Mark Scheme 2022 Practice Paper 3 - - - 1. (a) Start a clock when KCl is added to water 1 Record the temperature every subsequent minute for about 5 minutes 1 Al ... low record the temperature at regular time intervals until some time after all the solid has dissolved for M2 Plot a graph of temperature vs time 1 Extrapolate back to time of mixing = 0 and determine the temperature 1 Drawing of suitable graph could score M2, 3 and 4 (b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J 1 Max 2 if 14.6 °C used as ΔT Moles of KCl = 5.00 / 74.6 = 0.0670 1 Enthalpy change per mole = +1128.6 / 0.0670 = 16 839 J mol-1 1 = +16.8 (kJ mol-1) 1 Answer must be given to this precision (c) ΔHsolution = 1 ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chloride ions) ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chloride ions) ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1) 1 (d) Magnesium ion is smaller than the calcium ion 1 Therefore, it attracts the chloride ion more strongly / stronger ionic bonding 1 [Total 12 marks] 2 (a) (i) Correctly plots all points (± one square) and draws straight line of best fit 1 Lose this mark if the candidate’s line is doubled or kinked. Lose this mark if the line does not pass within one square of the origin, extending the line if necessary. Plotted points cover over half of grid 1 (ii) 0.046 ± 0.002 (mol dm−3) 1 0.088 to 0.096 (mol dm−3) 1 Allow M1 × 2 Allow two marks for correct answer. Answer must be to at least two significant figures - - [Show More]
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