Find the chloride concentration of sea water by titrating with silver nitrate, using chromate(VI) as the indicator. Read the question, answer each part on paper, then work through it below and see how many of the 18 marks you would earn. The worked example shows a full-mark answer with the mark scheme point each line scores.
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Name the apparatus with its capacity and precision (a 50.00 cm3 burette, a 250.0 cm3 volumetric flask), give quantities you can actually measure, and put the steps in an order someone else could follow.
Show the working, carry the full value through, and give the answer to the number of significant figures or decimal places the data support, with units and the sign of an enthalpy change.
Headings with units, consistent decimal places, crosses plotted to within half a square, and a line of best fit drawn the way the question asks: straight, curved or extrapolated.
Pick the weakness that matters most for this method (heat loss, gas escaping, an end point hard to see), explain its effect on the result, and give an improvement that fixes that weakness.
The question on this page is rephrased from a Cambridge International past paper for teaching. The figures, wording of the workout and the worked example are our own; the marking follows the published mark scheme. The original question paper is available from Cambridge.