Identification of ions and gases

Learning objectives

Describe the tests for the cations aluminium, calcium, chromium(III), copper(II), iron(II), iron(III) and zinc using aqueous sodium hydroxide and aqueous ammonia (colour of the precipitate and whether it dissolves in excess), and the test for ammonium ions by warming with aqueous sodium hydroxide to release ammonia

Describe the flame tests used to identify lithium (red), sodium (yellow), potassium (lilac), calcium (orange-red), barium (light green) and copper(II) (blue-green) ions

Describe the tests for carbonate ions (add dilute acid and test the gas with limewater) and for chloride, bromide and iodide ions (acidify with dilute nitric acid, then add aqueous silver nitrate to give white, cream and yellow precipitates)

Describe the tests for nitrate ions (reduce with aluminium foil and aqueous sodium hydroxide, then test for ammonia), sulfate ions (acidify with dilute nitric acid, then add aqueous barium nitrate to give a white precipitate) and sulfite ions (add acidified aqueous potassium manganate(VII), which changes from purple to colourless)

Describe the tests for the gases ammonia (turns damp red litmus paper blue), carbon dioxide (turns limewater milky), chlorine (bleaches damp litmus paper), hydrogen (squeaky pop with a lighted splint), oxygen (relights a glowing splint) and sulfur dioxide (turns acidified aqueous potassium manganate(VII) from purple to colourless)

Plan and interpret a sequence of qualitative tests to identify an unknown salt, recording observations and conclusions in the way expected in Paper 5 and Paper 6