Halide Ions

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Trends in Halide Ions

Reducing power of Halides INCREASES down the group

To reduce something, the halide has to lose an electron from the outer shell. How easy this is depends on the attraction between the nucleus and the outer electrons

As we go down a group, the attraction gets weaker because:

  • The ions are bigger, so the electrons are further away from the nucleus
  • There are extra inner electrons shells, so there is a greater shielding effect

When the halides reacts with Sulfuric Acid, the following happens

  • Fluorine/Chlorine - Not strong enough reducing agent to reduce the sulfuric acid, so HX (X being the halide) is formed
  • Bromine - Bromine is strong enough to reduce sulfuric acid, it happens in a redox reaction. The products formed are bromine (diatomic), sulfur dioxide and water
  • Iodine - Undergoes 2 redox reactions, first one produces Iodine (diatomic), sulfur dioxide and water, When iodine reacts with sulfur dioxide, it produces H2S, Iodine (diatomic) and water
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Test for Halides

Silver Nitrate is used to test for Halides

Ag+(aq) + X-(aq) ---> AgX(s) ... where X is F,Cl,Br or I

The colour of the preticipates are

  • Fluoride - No precipitate
  • Chloride - White Precipitate
  • Bromide - Cream Precipitate
  • Iodide - Yellow Precipitate

Then to test for a second time, you can add ammonia solution

  • Chloride Precipitate - Dissolves in DILUTE ammonia solution
  • Bromide Precipitate - Dissolves in CONCENTRATED ammonia solution
  • Iodide - INSOLUBLE in concentrated ammonia soulution
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These are very good concise notes, i assume from the revision guide as they are so similar to my own! :)

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