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Quantitative Analysis · Part 2 of 3
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
State what each of the burette, the pipette and the conical flask should be rinsed with before a titration.
Explain the effect on the calculated concentration if a student rinses the conical flask with the sample solution instead of distilled water.
A student obtains three titres agreeing to within 0.05 mL but the final concentration is 8% higher than the manufacturer's stated value. Analyse what this tells you about the errors in the investigation, and justify a set of checks to locate the problem.
State three properties a substance must have to be used as a primary standard, and give one example of a substance that is a primary standard and one that is not.
Explain why phenolphthalein rather than methyl orange must be used when titrating ethanoic acid in vinegar with sodium hydroxide.
A student standardises their sodium hydroxide solution against sodium carbonate, then uses it to titrate vinegar. A classmate argues the standardisation is a waste of time because the NaOH bottle is labelled 0.100 mol L−1. Evaluate this argument and justify whether the standardisation is necessary.
Describe how three significant variables were controlled in a titration investigation.
Explain the difference between a random error and a systematic error in a titration, giving one example of each, and explain why repeating a titration helps with only one of them.
A student writes in their evaluation: "My results were accurate because my three titres agreed to within 0.05 mL." Justify why this statement is chemically unsound, and describe what evidence would be needed to support a claim of accuracy.