Chemistry C3 Part 2

Based on Edexcel Textbook

pg 90-91 Looking for anions

Once the cations have been found you need to do a test to look for the anions (the negative ions). A preliminary test to look for hydroxide ions is to add litmus or universal indicator paper which will both turn a blue/purple.

If hydroxide ions aren't present add hydrocholic acid. Bubbles will be produced if carbonate or sulfite ions are present. To define between the two test which gas was present. It will be carbon dioxide for a carbonate but an acidic sulfur dioxide gas will mean it is a sulfite present.

To test for sulfate ions add barium chloride solution a white precipitate will be formed if sulfate ions were present but carbonate and sulfite ions also produce a white precipiate so to be sure which ion is present hydrochloric acid needs to be added as it will have no effect on the barium sulfate but sulfite and carbonate precipitates will be dissolved.

The halide ions (chloride, bromide and iodide) can be identified by adding silver nitrate solution adicified with dilute nitric acid. ( the dilute nitric acid is needed to remove any carbonate, sulphite or hydroxide ions present as they also form a precipitate). Different coloured precipiates will be formed for each halide ions. Chloride is white, Bromide is cream and Iodide is pale yellow.

pg 92-93 Analysis in Action

Analytical Chemists can be involved in a wide…