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18 exam-style questions with model answers, plus 24 quick multi-choice questions — every question on the site for this standard, grouped by the 6 pages of notes they come from.
Write a full answer before you reveal the model one — that comparison is where the marks come from. Every block links back to the notes that teach it.
Explain why the purpose "to find out which brand of orange juice contains the most vitamin C" does not meet this standard, and rewrite it so that it does.
Explain why a 1 : 1 acid–base titration is not suitable for this standard, and describe two alternatives that would be.
A student proposes to investigate how the ascorbic acid content of kiwifruit changes during ripening, using five fruit picked on five different days. Evaluate this design and justify the improvements you would make.
Explain what a primary standard is, state the properties one must have, and give two examples of redox titrants that are NOT primary standards.
Explain why warming is required when standardising permanganate against sodium oxalate, and explain how this relates to the reaction occurring.
A student investigating how ascorbic acid content changes over ten days analyses one sample per day, using the same bottle of iodine solution throughout and standardising it only on day one. Their results show a steady decline. Justify why this conclusion cannot be trusted, and evaluate what would be needed to secure it.
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.
A student's titres for one sample are 21.40, 20.85, 20.90 and 20.80 mL. Identify the concordant titres, calculate the mean, and explain why the first value is excluded.
Explain how a conclusion for this standard should be written so that it links the processed data to the purpose, and illustrate with an example.
A student's five data points show a clear downward trend, but one point sits 25% above the line. Evaluate how this should be handled in the report, and justify your recommendation.
Describe two possible sources of error in a titration-based investigation and state the direction each would bias the result.
Explain the difference between the precision and the validity of a set of results, and explain why a set of highly precise results can still fail to support a conclusion.
A student's evaluation reads: "There may have been human error. The results could be improved by repeating the experiment more times and being more careful." Evaluate this against the Excellence criterion and justify what a comprehensive evaluation would contain instead.