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AQA Jun 2017 Paper 1 Q3
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![The ionic product of water, Kw = 2.931015 mol2 dm6 at 10 C . 1 Which is the correct expression for Kw? Tick () one box. [H A Kw = O] [H2 ] ][OH B Kw = [H+][H2O] C Kw = [H+][OH] D Kw = [H ][OH O] [H [1 mark] 0 3 0 3 0 3 . 2 0 3 . 3 Calculate the pH of pure water at 10 C Give your answer to two decimal places. [2 marks] pH of water Suggest why this pure water at 10 C is not alkaline. [1 mark] *06* IB/M/Jun17/7405/1<br />
0 3 . 4 Calculate the pH of a 0.0131 mol dm3 solution of calcium hydroxide at 10 C Give your answer to two decimal places.[3 marks] pH of solution 0 3 . 5 The 0.0131 mol dm3 calcium hydroxide solution at 10 C was a saturated solution. A student added 0.0131 mol of magnesium hydroxide to 1.00 dm3 of water at 10 C and stirred the mixture until no more solid dissolved. Predict whether the pH of the magnesium hydroxide solution formed at 10 C is larger than, smaller than or the same as the pH of the calcium hydroxide solution at 10 C Explain your answer. [2 marks] pH of magnesium hydroxide compared to calcium hydroxide Explanation *07* Turn overIB/M/Jun17/7405/1<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_QP_-_Paper_1_AQA_Chemistry_A-Level_3-0.jpg)
![Total Question Answers 03.1 03.2 Ans = C [H+] = Kw =2.93 x 1015 (= 5.41 x 108) pH = ( log (5.41 x 108) = 7.27 03.3 [H+] = [OH-] [OH] = 0.0131 x 2 = 0.0262 [H+] = (Kw / [OH] ) = 2.93 x 1015 / 0.0262 (= 1.118 x 1013) pH = ( log (1.118 x 1013) = 12.9514 = 12.95 03 4 Or [OH] = 0.0131 x 2 = 0.0262 pOH = (log 0.0262) = 1.5817 pH =(log Kw pOH = log 2.93x10151.58 =14.531.58) = 12.95 Mark MARK SCHEMEA-LEVEL CHEMISTRY7405/1JUNE 2017 Additional Comments/Guidance Must be 2dp 7.27 scores 2 marks allow description in words equal moles/quantities/numbers/ratio of H+ and OH- pH = 12.95 scores 3 marks pH = 12.42 scores 2 marks (Kw = 1x10-14) pH = 12.65 scores 1 mark (not multiplied by 2) pH = 12.35 scores 1 mark (divided by 2) pH = 12.12 scores 0 marks (no x2 and wrong Kw) allow to 2dp or more 18 of 35<br />
MARK SCHEMEA-LEVEL CHEMISTRY7405/1JUNE 2017 03.5 smaller / lower pH / less alkaline / more acidic (magnesium hydroxide) is less soluble / sparingly soluble/ solubility of hydroxide increases down group II Total If not smaller CE = 0/2 Allow pH number between 8 and 12 M2 dependent on M1 but if blank mark on Ignore concentration and dissociation Ignore incorrect formula Do not allow Mg(OH)2 is insoluble 19 of 35<br />](https://learnah.org/wp-content/uploads/2018/08/June_2017_MS_-_Paper_1_AQA_Chemistry_A-Level_3-0.jpg)
