Parts (c), (d) and (e) – Indicative of the recent trend for the dumbing down of the exam – rather than getting the students to work out that a buffer solution is present, the fact that calculations relating to the concentrations of the remaining acid and salt are included BEFORE asking the pH, mean that there is a lot of hand holding and guiding students to the correct answer. For a comparison take a look at 1996, 2(c) where a similar question was asked (pH of a buffer) but no such specific clues were given.
The “per mole” part of the units for DH and DS will definitely screw up some candidates calculations. Again, part (d) is the type of HUGE clue to part (e) that we are beginning to see more and more of and never did in the past. (If you have any doubt, take a look at 1996, 3(d) for comparison purposes).
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As I predicted, hopelessly easy. Part (a)(ii) will cause a headache at the reading since I feel many students will interpret the question to mean that they should include the moles of NaNO3 “formed”. I think this is a poorly worded question and the examiners have given themselves an unnecessary headache – I am surprised that it got on to the exam paper. The third example of the dumbing down occurs in part (c). The excellent candidates are being penalized by the exam telling the students about oxidizing and reducing agents – this levels the playing field to too great a degree and such clues have seldom been given in the past (according to my records this has only happened three times before; 1968, 1978 and 1979) and I don’t think such blatant help SHOULD be provided.
Parts (d) and (e) continue the “dumbing down” theme. In part (d)(iii) the formula is set-up to make part (e) ridiculously easy. In the past there has never been so much hand-holding and direction for determining the effect of experimental error (see 1999,5(e) as an example).
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