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AQASpec 4.8Foundation & Higher~25 min

Chemical Analysis

Chemistry · Topic revision workspace

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Topic overview

What you need to know

Chemical Analysis is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. A single element or compound with a fixed melting and boiling point. Not a mixture. Two or more substances not chemically bonded, which can be separated by physical methods. A technique for separating mixtures of dissolved substances based on how they move through a stationary phase with a solvent. Rf = distance moved by substance ÷ distance moved by solvent.

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

  • Pure Substance: A single element or compound with a fixed melting and boiling point. Not a mixture.
  • Mixture: Two or more substances not chemically bonded, which can be separated by physical methods.
  • Chromatography: A technique for separating mixtures of dissolved substances based on how they move through a stationary phase with a solvent. Rf = distance moved by substance ÷ distance moved by solvent.
  • Rf Value: Retention factor: distance moved by substance ÷ distance moved by solvent front. Used to identify substances.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

  • Flame Test: A method to identify metal ions by the colour of flame they produce. Li⁺ = crimson, Na⁺ = yellow, K⁺ = lilac, Cu²⁺ = green/blue.
  • Test for Hydrogen: Hold a burning splint near the gas. Hydrogen makes a squeaky pop.
  • Test for Oxygen: Insert a glowing splint into the gas. Oxygen relights a glowing splint.
  • Test for Carbon Dioxide: Bubble the gas through limewater (calcium hydroxide solution). CO₂ turns limewater milky/cloudy.

Core knowledge

Key facts for Chemical Analysis

1

Pure Substance

A single element or compound with a fixed melting and boiling point. Not a mixture.

2

Mixture

Two or more substances not chemically bonded, which can be separated by physical methods.

3

Chromatography

A technique for separating mixtures of dissolved substances based on how they move through a stationary phase with a solvent. Rf = distance moved by substance ÷ distance moved by solvent.

4

Rf Value

Retention factor: distance moved by substance ÷ distance moved by solvent front. Used to identify substances.

5

Flame Test

A method to identify metal ions by the colour of flame they produce. Li⁺ = crimson, Na⁺ = yellow, K⁺ = lilac, Cu²⁺ = green/blue.

6

Test for Hydrogen

Hold a burning splint near the gas. Hydrogen makes a squeaky pop.

7

Test for Oxygen

Insert a glowing splint into the gas. Oxygen relights a glowing splint.

8

Test for Carbon Dioxide

Bubble the gas through limewater (calcium hydroxide solution). CO₂ turns limewater milky/cloudy.

Active recall

Close the notes and answer these

  1. 1.Without looking, explain pure substance and give one example or consequence.
  2. 2.Without looking, explain mixture and give one example or consequence.
  3. 3.Without looking, explain chromatography and give one example or consequence.
  4. 4.Without looking, explain rf value and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

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