爲什麽在標準硫代硫酸鈉的實驗中加入硫酸後要立刻滴定?

from the Wikipedia article on sodium thiosulfate:

QuoteThiosulfate anion characteristically reacts with dilute acids to produce sulfur, sulfur dioxide and water:[1]

S2O32−(aq) + 2H+ (aq) → S(s) + SO2(g) + H2O(l)


So it's not that it needs sulfuric acid - any acid will do. Sulfuric acid can act as a weak oxidizing agent in the right circumstances, but this isn't it. In fact, the thiosulfate ion is actually its own oxidizing andreducing agent in acid. The two sulfur atoms exist in different oxidation states, with an average of +2. One sulfur atom then goes to +4 while the other goes to zero.


That means a competing reaction exist along side with your titration reaction.

So. Do the titration as soon as possible.

謝謝，不錯的信息～～～，很有用