Aqa Chemistry

Test for negative ions:

Carbonates?

Halides (chloride, bromide and iodide)?

Sulfates?

Nitrates?

Carbonates: Add a dilute acid (such as hydrochloric acic) to a carbonate it fizzes and produces carbon dioxide gas. When burnt copper carbonate in green and goes black and white zinc carbonate turns lemon yellow.

Halides: If we add diute nitric acid and silver nitrate solution to a unknown substance, the appearance of a pecipitate tells us that one of the halide ions is present. Chloride ions give a white precipitate, bromide ions give a cream precipitate and iodid ions give a yellow precipitate.

Sulfates: Produce a white precipitate when we add hydrochloric acid to them followed by bariun chloride solution.

Nitrates: We add sodium hydroxide solution and a little aluminnium powder to produce ammonia gas.

Test for positive ions:

Flame tests:

Sodium hydrosxide solution:

Coloured precipitates:

Ammonium ions:

Flame tests: Identifying metals in group 1 and 2 can be done with flame tests. Put a small amount onto a PLATINUM wire loop and dip in hydrochloric aced. Lithium - Bright Red. Sodium - Golden yellow. Pottasium - Lilac. Calcuim - Brick Red and  Barium - Green.

Soduim hydroxide solution: Aluminium, calcuim and magnesium ions all form WHITE PRECIPITATES with sodium hydroxide. If we add more sodium hydroxide then the aluminium ions dissolve. Calcium and magnesium ions can be distinguised by the flame test anyway.

Colured precipitates: When added to sodium hydroxide metal ions may become coloured. Copper ions - blue precipitate. If a substance contains Iron - dirty green. Solution is added to iron ions - Redish brown precipitate is formed.

Ammonium ions - Produce Ammonia when sodium hydroxide solution is added and the solution is warmed gently.