AQA Chemistry (2013) Unit 3

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  • Created on: 15-05-13 17:00

3.4.1 Tests for Positive Ions

·         Flame tests

o   Lithium (Li+) – crimson

o   Sodium (Na+) – yellow

o   Potassium (K+) – lilac

o   Calcium (Ca2+) – red

o   Barium (Ba2+) – green

o   Magnesium (Mg2+) – no colour

·         Reactions with NaOH

o   Aluminium, calcium and magnesium – white precipitates

o   If more NaOH added, aluminium precipitate dissolves

o   Copper (II) – blue precipitate

o   Iron (II) – green precipitate

o   Iron (III) – brown precipitate

3.4.2 Tests for Negative Ions

·         Carbonates

o   2H+ (aq) (acid) + CO23- (aq) (carbonate ion) = CO2 (g) + H2O (l)

o   Bubble through limewater – white precipitate (cloudy)

·         Halides (chloride, bromide, iodide)

o   Add dilute nitric acid

o   Then add silver nitrate solution

o   Chloride – white

o   Bromide – cream

o   Iodide – pale yellow

·         Sulphates

o   Add dilute HCl

o   Then add barium chloride solution

o   Sulphate present – white precipitate

§  Ba2+ (aq) + SO42- (aq) = BaSO4 (s)

3.4.3 Titrations

·         Used to know exact volumes of acid and alkali will neutralise


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