Q21 · 2021 · Paper 1Unclassified3 marks
QUESTION 21 (3 marks)
Calculate the pH of a 0.1 M aqueous solution of Ba(OH)2, assuming complete dissociation. Show your working.
WORKED SOLUTION
3 marksQCAA guide · typeset solution
QCAA sample response and mark allocation
21 | [OH−] = 2 × [Ba(OH)2] = 2 × 0.1 = 0.2 M pOH = –log[OH−] = –log0.2 = 0.7 pH = 14 ‒ pOH = 14 – 0.7 = 13.3pH = 13.3 (to one decimal place) | • correctly determines [OH−] = 0.2 M[1 mark]• determines pOH = 0.7[1 mark]• determines pH = 13.3[1 mark] | Allow FT error for pOH and pH from OH−= 0.1 M only. Do not penalise for incorrect decimal places/significant figures. |
QCAA sample response and marking criteria reproduced from the official guide.
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