Explain why instrumental methods of analysis are often preferred over traditional chemical tests when identifying substances in a sample. In your answer, refer to the speed, sensitivity and accuracy of instrumental methods.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Scientists working in a forensic laboratory need to identify very small traces of unknown substances found at a crime scene. They must produce reliable results quickly.
Model answer (5 marks)
Instrumental methods are faster, giving results within seconds to minutes, whereas traditional tests can take hours.
They are highly sensitive, detecting trace amounts (ng–µg) that chemical tests miss.
They provide greater accuracy and reliability, giving quantitative data rather than qualitative.
They can distinguish between substances that give similar colour or precipitate reactions, and can identify components of mixtures.
They generate data that can be stored and matched against reference libraries, enabling definitive identification of unknowns.
They are highly sensitive, detecting trace amounts (ng–µg) that chemical tests miss.
They provide greater accuracy and reliability, giving quantitative data rather than qualitative.
They can distinguish between substances that give similar colour or precipitate reactions, and can identify components of mixtures.
They generate data that can be stored and matched against reference libraries, enabling definitive identification of unknowns.
Examiner tips
- Use the word ‘faster’ and give a time comparison; mention sensitivity in terms of trace detection; state accuracy as quantitative data; note the ability to resolve similar substances; highlight database matching.
- Show the five points in separate sentences or bullet‑style points to demonstrate clear structure.
Common mistakes
- Mixing up speed with sensitivity; not mentioning trace detection; claiming accuracy without specifying quantitative data; forgetting the database comparison; using vague terms like ‘better’ instead of ‘more accurate’.
Mark scheme (5 marks)
- Instrumental methods are faster / give results more quickly than traditional chemical tests
- Instrumental methods can detect very small / tiny amounts (traces) of a substance — they are more sensitive
- Instrumental methods are more accurate / more reliable than traditional tests
- Instrumental methods can identify substances that traditional chemical tests cannot distinguish between / can identify mixtures of substances
- Instrumental methods produce data that can be stored / compared to a database / reference library to identify an unknown substance
Key terms in this question
instrumental methods · sensitivity · accuracy
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Instrumental analysis questions
- A sports drink manufacturer wants to check that a new batch of drink contains th…
- A forensic scientist is analysing an unknown white powder found at a crime scene…
- A pharmaceutical company produces a painkiller tablet. Quality control scientist…
- A water company routinely monitors its treated drinking water for traces of diss…