AS Chemistry cation identification tests a visual guide

AS Chemistry cation identification tests a visual guide Designed by Samuel Millar

KEY suspected aqueous cation (colour indicated) { reagent solution: Na. OH (aq) NH 3 (aq) KSCN(aq) K 2 Cr. O 4 (aq) precipitate solution smoke sodium hydroxide solution ammonium hydroxide solution potassium thiocyanate solution potassium chromate solution

COPPER (II) NH 3 (aq) (add dropwise) Cu 2+(aq) pale blue ppt soluble in excess: deep blue soln (complex ion solution) Na. OH (aq) Cu 2+(aq) pale blue ppt insoluble in excess

IRON (III) NH 3 (aq) or Na. OH (aq) Fe 3+(aq) rust-brown ppt insoluble in excess KSCN (aq) Fe 3+(aq) blood red soln (complex ion solution)

IRON (II) NH 3 (aq) or Na. OH (aq) Fe 2+(aq) dirty green ppt insoluble in excess

BARIUM (II) KCr. O 4 (aq) Ba 2+(aq) yellow ppt soluble in hydrochloric acid: yellow soln

AMMONIUM Na. OH(aq) NH 4+(aq) HEAT pungent colourless gas evolved reacts with hydrogen chloride vapour: white smoke

ALUMINIUM (III), ZINC (II), MAGNESIUM (II) These cations all produce white precipitates with Na. OH and NH 3 solutions. The precipitates have the following solubilities in excess: Al 3+ (aq) NH 3 (aq) insoluble Na. OH soluble: (aq) colourless soln (ppt amphoteric) Zn 2+ (aq) Mg 2+ (aq) soluble: insoluble colourless soln (complex ion soln) colourless soln (ppt amphoteric)

FLAME TESTS Cation Li+ Na+ K+ Ca 2+ Sr 2+ Ba 2+ Cu 2+ Burning glass Flame colour Crimson-red Yellow/orange Lilac/pink through blue glass Brick red Red Green Blue-green Orange!