Chemical Analysis | AQA GCSE Chemistry Notes | Topic 8
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Pure substance: a single element or compound, not mixed with any other substance.
Pure elements and compounds melt and boil at specific temperatures.
Formulation: a mixture that has been designed as a useful product e.g. paint.
Chromatography can be used to separate and identify parts of a mixtures.
Chromatography has a stationary phase (paper) and mobile phase (solvent).
Some parts of the mixture are more soluble than others, so they travel different distances in the mobile phase.
Rf = distance moved by substance/ distance moved by solvent (0 to 1).
Tests for gases
Hydrogen: burning splint will produce a squeaky pop
Oxygen: glowing splint will relight
Carbon dioxide: bubble in limewater and shake and it will turn cloudy.
Chlorine: use damp litmus paper and it will bleach and turn white.
Tests for metal ions
Lithium: crimson
Sodium: yellow
Potassium: lilac
Calcium: orange-red
Copper: green
Sodium hydroxide test (add sodium hydroxide and it forms these precipitates)
Aluminium: white
Calcium: white
Magnesium: white
Copper(II): blue
Iron(II): green
Iron(III): brown
Test for carbonates: since acid + metal carbonate forms salt + water + carbon dioxide, react supposed carbonate with acid and then do carbon dioxide test.
Halide test: react with silver nitrate (and dilute nitric acid). Forms precipitate.
Silver Chloride: white
Silver Bromide: cream
Silver Iodide: yellow
Sulfate test: react with barium chloride solution (and HCl) and it forms a white precipitate.
Instrumental methods are an accurate, sensitive and rapid way to detect and identify elements and compounds.
Flame emission spectroscopy is an example.
The sample is put into a flame and the light given out is passed through a spectroscope.
The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.