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When CrI3 reacts with H2O2 in the presence of NaOH to give Na2CrO4, NaIO4 and H2O, how many times greater is the rate of disappearance of NaOH compared with the rate of disappearance of CrI3?

1. 5
2. 3
3. 10
4. 27

Correct answer: 5

Solution

The balanced equation is 2 CrI3 + 27 H2O2 + 10 NaOH -> 2 Na2CrO4 + 6 NaIO4 + 32 H2O, so NaOH disappears 10/2 = 5 times as fast as CrI3.

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