2.39 describe tests for the gases

i hydrogen

• burns with a 'squeaky pop' sound

ii oxygen

• will relight a glowing splint

iii carbon dioxide

• Turns lime water cloudy

iv ammonia

• Damp red litmus paper blue
• Damp universal indicator purple

v chlorine

• bleaches damp litmus paper white

2.38 describe tests for the anions

i) Cl-, Br- and I-, using dilute nitric acid and silver nitrate solution

• Chloride ions + nitric acid + silver nitrate > white precipitate (silver chloride)
• Bromide ions + nitric acid + silver nitrate > cream precipitate (silver bromide)
• Iodide ions + nitric acid + silver nitrate > yellow precipitate (silver iodide)

ii) SO4 2- (sulphate ions) using dilute hydrochloric acid and barium chloride solution

• SO4(2-) + HCl + Ba(2+) > white precipitate (barium sulphate)

iii) CO3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved

• Carbonate + acid > salt + water + carbon dioxide
• Carbon dioxide produced will turn lime water cloudy

2.37 describe tests for the cations

i) Li+, Na+, K+, Ca2+ using flame tests

• Lithum: red
• Sodium: orange (so strong can mask other colours)
• Potassium: lilac
• Calcium: brick red

ii) NH4+, using sodium hydroxide solution and identifying the ammonia evolved

• NH4 + OH > NH3 + H2O
• ammonium ions + hydroxide ions > ammonia + water
• ammonia (pungent smelling gas) turns red litmus paper blue

iii) Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution

• Copper(ii) sulphate + sodium hydroxide > blue precipitate
• Iron(ii) sulphate + sodium hydroxide > green precipitate
• Iron(iii) sulphate + sodium hydroxide > brown precipitate