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Quantitative Investigation · Part 2 of 3
6 exam-style questions with model answers, plus 8 quick multi-choice questions — every question on this part of the standard, grouped by the 2 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
State why potassium permanganate titrations need no indicator, and state which acid must be used to acidify them and why.
Explain why starch is added only near the endpoint in an iodine–thiosulfate titration, and explain the effect of adding it at the start.
Justify each step of an iodometric determination of hypochlorite in bleach in relation to the reactions occurring and the nature of the sample.
State the Beer–Lambert law, define each symbol with its unit, and explain why absorbance is proportional to concentration in a colorimetry experiment.
Explain why the standard curve must cover an appropriate range, and explain what would go wrong if a sample's absorbance fell above the highest standard.
Compare colorimetry with titration as analytical techniques for a trend investigation, and justify which you would choose to measure copper(II) concentration in a series of soil extracts.