“The reaction between an alkali and two different solutions of an acid” is one of the most common 0620 practical questions. By hand, pour acid A into the burette, run some out so the level is on the scale, measure 25 cm³ of alkali in the measuring cylinder, add the indicator, then turn the tap and swirl until the colour just changes. Rinse the burette and do it again with acid B. Then complete the results table, compare the two acids and evaluate the method. The concentrations change every attempt. Allow about 30 minutes.
Checked: Cambridge IGCSE Chemistry 0620 Papers 5 and 6, 2020 to 2025. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
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All four burette readings recorded and matching your burette, each final reading larger than the initial one, both volumes worked out correctly, every value to 0.1 cm³ (one decimal place), a volume of acid A close to the supervisor’s, and a volume of B that is the right multiple of your volume of A.
The colour change of the indicator, which acid is more concentrated and why (it needed the smaller volume), how many times more concentrated from your own two volumes, and a predicted volume for a different amount of alkali, with its unit.
Why the indicator changes colour at the end point, the advantage of a volumetric pipette, how to check reliability, the main source of error, and why the burette is rinsed with the new solution.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.