Practise 15 exam-style questions on Instrumental methods (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
15 questions
1–6 marks each
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15 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
Instrumental methods are described as sensitive and accurate.
Explain what is meant by sensitive and by accurate.
Model answer
Sensitive means the method can detect very small amounts or very low concentrations of a substance. Accurate means the result is close to the true value, so the substance is identified correctly and the amount measured is correct.
Explanation
Do not confuse accurate (close to the true value) with repeatable (giving the same result each time). Sensitivity is about the smallest amount that can be detected.
Mark scheme
1 mark
sensitive: can detect very small amounts / low concentrations of a substance
allow can work with very small samples
1 mark
accurate: the result is close to the true value / correctly identifies the substance
do not accept 'gives the same result each time' for accurate
Question 2
2 marks
A sample contains a mixture of several different metal ions.
Explain why an instrumental method is more useful than chemical tests for identifying the metal ions in the sample.
Model answer
In chemical tests, the result for one ion can hide another; for example, the yellow flame of sodium masks other flame colours. An instrumental method such as flame emission spectroscopy produces separate lines for each metal ion, so every ion in the mixture can be identified.
Explanation
Chemical tests work best on a single pure compound. Instruments can pick out each component in a mixture, which is another important advantage.
Mark scheme
1 mark
in chemical tests the results for one ion can mask / interfere with those for another
allow e.g. flame colours can be masked / precipitate colours can be hidden
1 mark
an instrumental method can identify each ion in the mixture (e.g. each gives its own spectral lines)
Question 3
3 marks
Lead ions in drinking water are harmful even at very low concentrations. Water companies use instrumental methods to test for lead ions.
Explain why instrumental methods are used rather than chemical tests.
Model answer
Lead is harmful at very low concentrations, far too low for a chemical test such as forming a precipitate to detect. Instrumental methods are sensitive enough to detect these tiny amounts, and they also measure the concentration, so the company can check that it is below the safe limit.
Explanation
Two advantages matter here: sensitivity (detecting very low concentrations) and quantitative results (measuring how much is present). A precipitate test only says 'present' or 'not present', and only when there is enough to see.
Mark scheme
1 mark
the concentration of lead ions is very low
1 mark
chemical tests are not sensitive enough to detect such small amounts
allow instrumental methods are sensitive
1 mark
instrumental methods measure the concentration, so it can be checked against a safe limit
allow chemical tests only show whether an ion is present
Question 4
4 marks
Instruments are placed beside busy roads to monitor the concentration of pollutant gases, such as nitrogen dioxide, in the air 24 hours a day.
Suggest the advantages of using instruments rather than chemical tests for this monitoring.
Model answer
Instruments can work automatically and continuously, day and night, without anyone having to carry out tests. They give results immediately, so warnings can be issued as soon as pollution levels rise. They are sensitive enough to detect very low concentrations of pollutants, and they measure the actual concentration, so changes during the day can be recorded and compared with safety limits.
Explanation
Chemical tests need a person to carry them out and usually only show whether a substance is present. Continuous monitoring needs the speed, sensitivity and quantitative results that instruments provide.
Mark scheme
1 mark
can monitor continuously / automatically, without a person
max 4
1 mark
rapid: give results immediately so warnings can be issued when levels are high
1 mark
sensitive: can detect very low concentrations of the pollutant
1 mark
measure the concentration (quantitative), so changes over time can be recorded
1 mark
accurate results
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