11.3 some reactions of the halide ions

Describe the relative reactivity of halide ions as reducing agents

Halides’ reducing power increases down the group due to increase in ionic radii as the valence electrons are held less tightly and therefore can be lost more easily

Describe and explain the reaction of halide ions with aqueous silver ions followed by aq ammonia

Can be used to identify halide ions.

• A white precipitate of AgCl forms if chloride ions are present

• A cream precipitate of AgBr forms if bromide ions are present

• A yellow precipitate of AgI forms if iodide ions are present

Explain the addition of ammonia after the halide test

• The silver halide precipitates can look similar So need to confirm identity

• Add dilute ammonia

• If the precipitate dissolves, chloride

• If it does not dissolve, add concentrated ammonia

  • If it dissolves, bromide

• If it still does not dissolve, iodide

Describe and explain the reaction of halide ions with concentrated sulfuric acid

General equation:   H₂SO₄ (l) + X^– (aq) → HX (g) + HSO₄^– (aq)

Halides react with concentrated H2SO4 to produce toxic gases

Describe observations when chloride ion reacts with concentrated sulfuric acid

Steamy white fumes of HCl gas

Describe observations when bromide ion reacts with concentrated sulfuric acid

Reddish brown Br2 gas

Describe observations when sodium iodide reacts with concentrated sulfuric acid

H₂SO₄ (aq) + NaI (s) → HI (g) + NaHSO₄(aq)

Describe observations and write equation for the reaction of HI with concentrated sulfuric acid

Violet / purple I₂ vapour

Yellow solid of S

Strong, bad (egg) smell of H₂S

Describe and explain where the reaction of halide ions with concentrated sulfuric acid

Fume cupboard as gases produced are toxic