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Edexcel Jan 2012 Paper 4 Q23
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![Question Number 23 (a)(i) Acceptable Answers Reject Mark (Ka =) [H+][C6H5COO]/[C6H5COOH] Penalise missing charges ALLOW [H3O+] in place of [H+] IGNORE state symbols and units even if incorrect Ka = [H+]2/[C6H5COOH] Question Number 23(a)(ii) [H+] = (6.3 x 105 x 0.0025) Acceptable Answers Mark (1) pH =log (6.3 x 105 x 0.0025) = 3.4 (1) Answer without working scores (2) marks 6.8 scores (1) IGNORE sf except 1 Reject answer if units given Question Number 23(b) Acceptable Answers Reject Mark Water neutralizes acid (pH) range (of indicator) 3.8 to 5.4 OR pKin = 4.7 (1) Bubble bath is (initially yellow since) pH less than 3.8 / is 3.4 (1) Adding of water/dilution (of acid) causes pH to rise/ means [H+] decreases (1) Hence pH rises to5.4 so blue/changes colour (1) If a(ii) pH>3.8 and <5.4 then loses second marking point but can score other marking points. If a(ii) pH>5.4 then can score first and third marking points only TOTAL FOR SECTION C = 21 MARKS TOTAL FOR PAPER = 90 MARKS 6CH0401 1201<br />](https://learnah.org/wp-content/uploads/2018/08/January_2012_MS_-_Unit_4_Edexcel_Chemistry_A-level_23.jpg)