acidified 左之後點..........................chem勁人唔該入黎

in fact it is learnt in chemistry bachelor level...

H+ act as an catalyst, which speed up the reaction. note that some reactions
need acid medium to proceed, not the oxidizing agent need acid.

for example: use acidified potassium dichromate to oxidize aldehyde(RCHO).

in fact, aldehyde react with the proton(acid) first, and then free dichromate
attack the resulting species. And it is not right to say the oxidizing agent need
acid to carry out reaction. It is acceptable to say oxidation of aldehyde need
an acidic medium.

2008-08-30 19:37:06 補充：
If there is no acid, only aldehyde and dichrmoate, there will be no reaction since dichromate
will not react with unprotonated aldehyde.