✔ 最佳答案
anion is very obvious.
a gas which decolorize KMnO4, suggesting that it's a reducing agent.
together with the fact that it's acidic, it's quite sure that the gas is sulphur dioxide (colorless); and the anion is sulphite SO3(2-).
the flame is orange-red is not very clear; it can be sodium (golden yellow) or calcium (brick-red), depending on your observations.
However, the solid is insoluble, so the cation must be calcium: calcium sulphite is insoluble, but sodium sulphite isn't.
calcium sulphite.
p.s. i don't quite get (5). you mentioned that it's insoluble, then how can you tell white precipitate is formed? OR do you mean the white solid "remains undissolved"?
2010-12-01 19:02:58 補充：
calcium sulphite reacts with acid to give sulphur dioxide and calcium salts;
hydrochloric acid to give calcium chloride, which is soluble.
however, addition of alkali gives calcium hydroxide, which is only slightly soluble and tends to precipitate.
2010-12-01 19:04:47 補充：
so it's not really the "aqueous solution" of your sample; it's reaction mixture.
also, hydrochloric acid can be oxidized by permanganate, giving chlorine gas. permangnate is reduced to almost-colorless mananese(II) ion.
why don't you just put the solid into permanganate?
