chemical analysis

首先, lime water 係 calcium hydroxide
會令lime water milky 有兩種(限於我的Chem知識), 一種係carbon dioxide, 另一種係sulphur dioxide.
如果Jimmy加 acid 落solution, 通常test anion (∵hydrogen ion)
∴呢種solution有機會含有 carbonate ion or hydrogencarbonate ion →→ 出carbon dioxide
亦有機會係 sulphite ion →→ 出sulphur dioxide


如果要futher confirm what substance it might be,
只要加 oxidising agent, 因為只有sulphite ion會 reduce oxidising agent
e.g.加acidified potassium permanganate solution.
If it has sulphite ion, solution changes from purple to colourless.

如果同oxidising agent無reaction, then it may be carbonate ion or hydrogencarbonate ion.
Then we add Magnesium ion into sample
If white precipitate is formed(magnesium carbonate is solid), that is caronate ion.
If it still remain colourless(magnesium hydrogen carbonate is aqueous), that is hydrogencarbonate ion.

Since shlphite salt (SO32-) gives out SO2 gas upon reaction with acid and SO2 gas can also turn lime water milky:
SO2(g) + Ca(OH)2(aq) --> CaSO3(s) + H2O(l)
Therefore, to further confirm the existence of sulphite salt, we should further test the gas evolved by:

Acidified KMnO4/K2Cr2O7
Owing to the reducing property of SO2, it can decolourize acidified KMnO4 and turn Acidified K2Cr2O7 from orange to green:
5SO32-(aq) + 2MnO4-(aq) + 6H+(aq) --> 2Mn2+(aq) + 5SO42-(aq) + 3H2O(l)
3SO32-(aq) + Cr2O72-(aq) + 8H+(aq) --> 2Cr3+(aq) + 3SO42-(aq) + 4H2O(l)

Wet blue litmus paper, owing to the acidic and bleaching properties of SO2, the paper first turns red and then colourless.

2008-03-26 08:59:20 補充：
I'm not sure if I miss some tests or other possible substances may exist, but I first provide other tests for SO2 here first:
3. Choking smell of SO2
4. Its aqueous solution can decolourize chlorine gas.