1. Learning objective:
To be able to identify chemical species from their characteristic behaviour
22/05/2018
Anions
Sulfate (SO42-): Add dilute hydrochloric acid followed by barium chloride solution  thick white precipitate OR Add barium chloride solution then dilute hydrochloric acid  thick white precipitate remains on addition of acid Ba2+ (aq) + SO42- (aq)  BaSO4 (s)
Carbonate (CO32-): Add dilute hydrochloric acid  effervescence (fizzing) Bubble gas through limewater  turns milky owing to CO2 CO H+ (aq)  CO2 (g) + H2O (l) Group 2 carbonates (and Li2CO3) release CO2 on heating: MCO3 (s)  MO (s) + CO2 (g)

2. Anions
Halides (X-): Add dilute nitric acid followed by silver nitrate: White ppt chloride (Cl-)
Cream ppt bromide (Br-)
Yellow ppt iodide (I-) Ag+ (aq) + Cl- (aq)  AgCl (s)
Can be followed up by testing solubility of silver halide in ammonia: AgCl: soluble in dilute and concentrated ammonia AgBr: soluble in concentrated ammonia only AgI: insoluble in ammonia OR
Add concentrated sulfuric acid to solid halide: Cl-: steamy white fumes; turn damp blue litmus red Br-: steamy white fumes; followed by orange liquid/gas I-: Purple fumes/grey solid forms

3. Cations
Flame tests Clean nichrome wire in concentrated HCl and blue Bunsen flame Moisten wire and pick up solid sample. Hold sample in blue flame:
Li+ Na+ K+ (often masked by sodium ion – use blue filter to check) Ca2+ Sr2+ Ba2+
Ammonium ion (NH4+): Dissolve in sodium hydroxide solution Warm gently Test fumes with red litmus Red  blue demonstrates presence of ammonia gas (NH3) and so ammonium ions in original solid