✔ 最佳答案
1.
When the colourless solution of potassium bromide and the deep purple solution of potassium manganate(VIII) are mixed, the reaction mixture becomes brown.
2MnO4-(aq) + 16H+(aq) + 10Br-(aq) → 2Mn2+(aq) + 8H2O(l) + 5Br2(aq)
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2.
The purple potassium manganate(VII) solution is decolourized.
2MnO4-(aq) + 16H+(aq) + 10Cu(aq) → 2Mn2+(aq) + 8H2O(l) + 5Cu2+(aq)
Firstly, It is hardly to observe the blue colour of the Cu2+(aq) ions. This is because the Cu2+(aq) ions formed are very diluted, and the blue colour of Cu2+(aq) ions is pale. However, although the manganate(VII) ions are also very dilute, the purple colour of manganate(VII) ions is deep enough to be observed.
Secondly, the copper powder added is usually in large excess, and only a small amount of copper powder is reacted. Therefore, it is hardly to observe that the copper powder dissolves.
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3.
The green (actually blue) chromium(III) chloride solution changes to orange.
3S2O82-(aq) + 2Cr3+(aq) + 7H2O(l) → 6SO42-(aq) + Cr2O72-(aq) + 14H+(aq)
The reaction may be slow. Ag+(aq) may act as a catalyst to speed up the reaction.
2008-06-28 17:47:31 補充：
The last line is:
The reaction may be slow. Ag^+(aq) ions can be used as a catalyst to speed up the reaction.
