Weigh, dissolve, make up, titrate. Every step has a trap.
Making a standard solution and titrating against it comes up in almost every 9701 Paper 5. Here you make 250.0 cm³ of sulfamic acid solution by weighing by difference, then titrate sodium hydroxide against it. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge AS & A Level Chemistry 9701 Paper 5. It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 9701/52 October/November 2024, (preparing a standard solution of sodium carbonate) · official past papers
Practise next: 9701/52 February/March 2024, (weighing by difference and making up a standard solution) · official past papers
Practise next: 9701/52 October/November 2025, (standard solution and titration with potassium thiocyanate) · official past papers
Examiner reports used: 9701 November 2023, March 2024, June 2024, November 2024, March 2025, November 2025 and March 2026.
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What a full-mark diagram shows
Weighing
Weigh by difference on a top-pan balance: boat with solid, then the boat after tipping, so you know the mass actually transferred.
The standard solution
Dissolve in a beaker, pour through a funnel into a 250.0 cm³ volumetric flask, rinse everything into it, make up to the mark, stopper and invert.
The titration
25.0 cm³ volumetric pipette with a filler, burette rinsed with the acid, conical flask on a white tile, drop by drop near the end point.
Recording
Burette readings and titres to two decimal places; concordant titres within 0.10 cm³.
Habits the examiner reports keep asking for
Rinse into the flask. Missing the rinsings is the most common error in the reports.
Invert the stoppered flask several times. “Fill the flask” is not the same as making up to the mark.
Say “volumetric pipette”, with its capacity. “Pipette” alone is ambiguous.
Rinse with the solution it will hold, not just with distilled water, and give one answer, not two.
Safety needs a specific hazard and precaution, not just “gloves”.