🎯 Common Question Types:
- Rf calculation from a given chromatogram (1–2 marks) — always show formula and substitution
- "State two advantages of instrumental methods" (2 marks) — one mark per advantage
- Identifying a pure/impure sample from number of spots (1 mark)
- Flame emission spectroscopy and line spectra (2–3 marks) at HT
📝 Key Command Words:
- Calculate: Show Rf = d(substance) / d(solvent front), substitute values, give answer to 2 d.p.
- State: Give a brief factual answer — no explanation needed unless asked
- Identify: Name the element/substance from the evidence given
- Suggest: Apply your knowledge to a new context — there may be more than one correct answer
- Explain: Give a reason WHY, not just what happens
⚠️ Common Mistakes to Avoid:
- Dividing solvent distance by substance distance (upside-down Rf — gives a number > 1)
- Writing "Rf = 0.80 cm" — Rf has NO UNITS, never add cm
- Stating only one advantage of instrumental methods when the question asks for two
- Confusing the simple flame test colour with a line spectrum — they test different things
- Saying an impure sample "has fewer spots" — impure means MORE spots (multiple components)
This exam tips covers Exam Tips within Instrumental Analysis for GCSE Chemistry. Revise Instrumental Analysis in Chemical Analysis for GCSE Chemistry with 6 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Instrumental Analysis
Which formula correctly calculates the Rf value in chromatography?
State two advantages of using instrumental methods of analysis compared with traditional chemical tests.
Quick recall flashcards
What is the formula for calculating the Rf value in chromatography?
Rf = distance moved by substance ÷ distance moved by solvent front
Always between 0 and 1. No units.
In paper chromatography, what does the number of spots on a chromatogram tell you about purity?
One spot → pure substance (single component)
Multiple spots → mixture / impure sample (multiple components, each with different Rf)