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Aqueous Halides with Silver Nitrate

This video demonstrates how to test for halide ions using silver nitrate solution. Step 1: Add dilute nitric acid to remove carbonate impurities (already done before this video) Step 2: Add silver nitrate solution (1:49) Step 3: Observe the colour of the resulting precipitate Step 4: As an optional addition, you can add dilute or concentrated ammonia solution. This is useful because the colour of the precipitates formed in step 3 can be difficult to distinguish. The chloride precipitate is obviously white, but the other two aren't really very different from each other. You couldn't be sure which you had unless you compared them side-by-side. Chloride Ions Ag+(aq) + Cl-(aq) → AgCl(s) The resulting precipitate is white. As an additional test, the precipitate dissolves in dilute ammonia. Bromide Ions Ag+(aq) + Br-(aq) → AgBr(s) The resulting precipitate is pale cream. As an additional test, the precipitate dissolves in concentrated ammonia, but not dilute ammonia. Iodide ions Ag+(aq) + I-(aq) → AgI(s) The resulting precipitate is pale yellow. As an additional test, the precipitate does not dissolve in either dilute ammonia or concentrated ammonia. All of the precipitates change colour if they are exposed to light - taking on grey or purplish tints. This is called ‘photosensitivity’. This property can be used in photography. The fluoride ion does not form any precipitate when silver nitrate is added: silver fluoride is soluble in water. Unlike the other silver halides, it is not photosensitive. It has few uses.