Testing for ions and gases Topic 8.4

What you need to know The following tests: Cations - Iron(II), Iron(III), Copper(II), Aluminium, Zinc, Calcium and Ammonium Anions – Nitrate, Chloride, Iodide, sulfate, carbonate Gases- ammonia, carbon dioxide, chlorine, hydrogen, oxygen

Cations Positive ions Fe2+ Fe3+ Cu2+ Al3+ Zn2+ Ca2+ NH4+

Iron(II) - Fe2+ Dirty green precipitate Doesn’t dissolve in excess In both sodium hydroxide and ammonia solution

Iron (III) - Fe3+ Red brown precipitate Doesn’t dissolve in excess In both sodium hydroxide and ammonia solution

Copper(II)- Cu2+ Pale blue precipitate with sodium hydroxide doesn’t dissolve in excess Pale blue precipitate with ammonia solution dissolves in excess to give a deep blue precipitate

Aluminium - Al3+ White precipitate doesn’t dissolve in excess sodium hydroxide White precipitate does dissolve in excess ammonia solution

Zinc - Zn2+ White precipitate with sodium hydroxide and ammonia solution dissolves in excess of both

Calcium - Ca2+ White precipitate with sodium hydroxide and with ammonia solution Doesn’t dissolve in excess of either!

Distinguishing Al3+, Zn2+ and Ca2+ With sodium hydroxide and ammonia Dissolves in excess sodium hydroxide and ammonia White precipitate Doesn’t dissolve in excess of either sodium hydroxide or ammonia Dissolves only in excess sodium hydroxide Zn2+ Ca2+ Al3+

Ammonium ion - NH4+ Ammonias is displaced from its compounds when they heated with a strong base Heat with sodium hydroxide- gas given off that turns damp red litmus blue

Anions Negatively charged ions NO3- Cl- I- SO42- CO32-

Nitrate - NO3- Add sodium hydroxide and aluminium foil Gas evolved that turns damp red litmus blue

Chloride - Cl- Add nitric acid and then silver nitrate solution White precipitate

Iodide - I- Add nitric acid and then silver nitrate solution Pale yellow precipitate

Sulfate - SO42- Add a few drops of acid (not sulfuric) then barium nitrate or barium chloride solution White precipitate

Carbonate - CO32- Add acid Bubbles of gas that turns limewater milky

Gases NH3 CO2 Cl2 H2 O2

Damp red litmus paper turns blue Ammonia NH3 Damp red litmus paper turns blue

Carbon dioxide CO2 Turns limewater milky

Bleaches damp litmus paper Chlorine Cl2 Bleaches damp litmus paper

Hydrogen H2 Hold a lighted splint to the tube containing hydrogen, the gas burns with a squeaky pop POP!

Relights a glowing splint Oxygen O2 Relights a glowing splint

What you should know The tests for : Cations - Iron(II), Iron(III), Copper(II), Aluminium, Zinc, Calcium and Ammonium Anions – Nitrate, Chloride, Iodide, sulfate, carbonate Gases- ammonia, carbon dioxide, chlorine, hydrogen, oxygen