AQA Chemistry (2013) Unit 3
- Created by: Lex
- 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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