Investigating hydrogen halides

Outline the procedure

• react potassium halides with sulfuric acid —— hydrogen halides are produced and can react with hydrogen halides

• react potassium halides with phosphoric acid —— hydrogen halides are produced but cannot react with hydrogen halides

Test for sulphur dioxide

potassium manganate (VII) - it is decoloured by gas

Test for hydrogen sulphide

lead ethanoate solution - black precipitate of lead sulphide

Explain the appearance of each potassium halide when adding concentrated sulfuric acid

• Potassium Chloride - white misty fumes

• Potassium Bromide - orange fumes

• Potassium Iodide - purple fumes

Explain what happens when you add ammonia solution with potassium halide

• Potassium Chloride - white precipitate

• Potassium Bromide - cream precipitate

• Potassium Iodide - yellow precipitate

What is the effect of each potassium halide on damp blue litmus paper

• Potassium Chloride - Red

• Potassium Bromide - Red

• Potassium Iodide - Pink/Red

  • H+ ions released

Effect of potassium magnate solution on each potassium halide

• Potassium Chloride - no change

• Potassium Bromide - decolourised (SO2)

• Potassium Iodide - no change

  • initially added sulfuric acid

Effect of lead ethanoate solution on each potassium halide

• Potassium Chloride - no change

• Potassium Bromide - no change

• Potassium Iodide - black precipitate forms (H2S)

  • initially added sulfuric acid

Appearance when adding phosphoric acid to potassium halide

• Potassium Chloride - Fizzing

• Potassium Bromide - Fizzing

• Potassium Iodide - Fizzing

Solubility of product in water

• Potassium Chloride - very soluble

• Potassium Bromide - very soluble

• Potassium Iodide - very soluble

Effect of product in water

• Potassium Chloride - no change

• Potassium Bromide - lots of brown vapour produced

• Potassium Iodide - lots of purple vapour produced

Thermal stability ______ as you go down the group

decreases

When do you use phosphoric acid when reacting with potassium halide

To get a pure sample of potassium bromide and potassium chloride