Analysis & the Atmosphere is a core part of GCSE Chemistry. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Pure substanceOne element or compound — sharp melting point
MixtureTwo or more substances not chemically joined
FormulationUseful mixture made to exact quantities, e.g. paint
Mobile phaseThe solvent that moves up the paper
Stationary phaseThe paper the solvent moves through
BaselinePencil line where spots are placed at the start
Flame testHeat sample on wire — colour reveals the metal ion
PrecipitateInsoluble solid formed when two solutions mix
Sodium hydroxide testIdentifies metal ions by precipitate colour
Instrumental analysisMachine-based methods like spectroscopy
SensitiveDetects very small amounts of a substance
AccurateResult is very close to the true value
Rf valueDistance moved by spot ÷ distance moved by solvent
Solvent frontHighest point the solvent reaches on the paper
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
How does a pure substance melt?✗ Gradually over a wide range of temperatures. ✓ At a sharp, fixed temperature.
How does chromatography separate substances?✗ Only by colour — colourless substances can't be separated. ✓ By how strongly each is attracted to the paper versus the solvent.
What happens to electrons when sodium reacts with chlorine?✗ Sodium and chlorine share an electron between them. ✓ Sodium loses one electron to chlorine; the resulting Na+ and Cl- ions attract electrostatically.
Why do metals conduct electricity?✗ Metal atoms themselves move to carry the current. ✓ Delocalised electrons are free to move through the lattice of positive ions, carrying charge.
At which electrode are positive ions reduced during electrolysis?✗ Positive ions are reduced at the anode because that's where positive things go. ✓ At the cathode (the negative electrode) — positive ions gain electrons there.
Practise Analysis & the Atmosphere — free games
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