- 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.