2.38 describe simple tests for the anions:

2.38      describe simple tests for the anions:

i           Cl−, Br− and I−, using dilute nitric acid and silver nitrate solution

Silver chloride is insoluble in water (see Section 4.6).  Silver bromide and silver iodide are also insoluble.  Adding silver nitrate solution to a solution containing these ions will produce a precipitate of the insoluble silver halide.  The solution must be acidified in case there are any hydroxide or carbonate ions present that would also give a precipitate with the silver ions.

Take a few cm3 of the sample to be tested. Add a similar volume of dilute nitric acid. Then add a few drops of silver nitrate solution and look for a precipitate.
chloride (Cl-)	white precipitate of silver chloride Ag+(aq) + Cl-(aq) → AgCl(s)
bromide (Br-)	cream precipitate of silver bromide Ag+(aq) + Br-(aq) → AgBr(s)
iodide (I-)	yellow precipitate of silver iodide Ag+(aq) + I-(aq) → AgI(s)

ii          SO42−, using dilute hydrochloric acid and barium chloride solution

Barium sulfate is insoluble (see Section 4.6).  A white precipitate of barium sulfate will form if a solution of barium chloride is added to a solution containing sulfate ions.  The solution must be acidified in case there are any carbonate ions present that would also give a precipitate with the barium ions.  Take a few cm3 of the sample to be tested.  Add a similar volume of dilute hydrochloric acid.  Then add a few drops of barium chloride solution.

Ba2+(aq)   +   SO42−(aq)  ®     BaSO4(s)

iii         CO32−, using dilute hydrochloric acid and identifying the carbon dioxide evolved

If carbonate ions are present, carbon dioxide gas will be given off when dilute HCl is added. Take a few cm3 of the sample to be tested.  Add a similar volume of dilute hydrochloric acid.  Bubble the gas evolved through limewater and the limewater will turn milky.

This test will also work on a solid sample of a carbonate.  (See Section 4.5)

CO32-(aq) + 2H+(aq)  → CO2(g)   +   H2O(l)