Alternative paper 4

Please read these tests for the cations and anions for your Alternative paper 4.

Test for cations:
Add Dilute sodium hydroxide solution. Precipitate form, add aqueous ammonia solution or NaOH solution to see if the precipitate dissolves.

Observation for the following cations:
Fe2+ - Dark Green ppt
Fe3+ - Brown ppt
Cu2+ - Blue ppt
Ca2+, Mg2+ - White ppt - Do not dissolve in excess Ammonia solution or NaOH solution.
Al3+, Zn2+, Pb2+ - White ppt - Dissolve in excess.

Test for Anions:

Carbonate : Add dilute acid : Observation: bubbles/ effervescene - Test for the gas using limewater.

Sulphate: Add acid followed by barium chloride/ nitrate solution. (Any soluble barium salt + any soluble sulphate forms a white dense barium sulphate precipitate. ) then add dilute acid again. Observation: White ppt, insoluble in excess

Nitrate: Boil the nitrate in sodium hydroxide solution and add fine aluminium powder or aluminium foil. Observation: Ammonia gas is given off, (pungent smell)
Test for ammonia gas to confirm is that litmus paper turn from red to blue.

Test for halogens: Always add dilute nitric acid first, then silver nitrate solution.

Chloride: add dilute nitric acid and silver nitrate solution. Observation: white precipitate Bromide: add dilute nitric acid and silver nitrate solution. Observation: Cream ppt

Iodide: dilute nitric acid and silver nitrate solution. Observation : yellow ppt

Test for gases
Test for Carbon Dioxide: Limewater : Observation: turns limewater milky
Test for oxygen gas: Glowing split: Observation: Relights glowing splint
Test for hydrogen gas: Burning split. Observation: "POP" sound
Test for sulphur dioxide: potassium dichromate(VI) solution, observation: turns the solution from orange to green.
Test for ammonia gas : damp red litmus paper. Observation: Turns red litmus paper blue.
Test for chlorine: damp blue litmus. Observation: bleach the litmus paper