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Anion Lab
Manual
2. Aqueous Barium Nitrate
in Qualitative Analysis
b) Test For Sulphite ion, SO32-(aq)
Barium ions react with sulphite
ions to form a white precipitate of barium sulphite,
which dissolves in dilute nitric or dilute hydrochloric
acid to form a colourless solution. The H+
ions in the dilute acid reacts with the white precipitate
to from a soluble salt and sulphur dioxide gas. Sulphur
dioxide gas evolved turns orange acidified potassium
dichromate green in colour or decolourises purple acidified
potassium manganate(VII).
Ba2+ (aq) + SO32-
(aq) -----> BaSO3 (s)
BaSO3 (s) + 2H+
(aq) -----> Ba2+ (aq)
+ SO2 (g) + H2O (l)
It is important to note that dilute
sulphuric acid cannot be used as it introduces sulphate
ions that interfere with the test.
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