8. Consider the following mechanism, what is the role of water?

Question

Consider the following mechanism:

1. ClO^-(aq) + H₂O(l) <=> HClO(aq) + OH^-(aq) FAST

2. I^-(aq) + HClO(aq) => HIO(aq) + Cl^-(aq) SLOW

3. OH^-(aq) + HIO(aq) => H₂O(l) + IO^-(aq) FAST

What is the role of water?

Detailed explanation please

The answer is: catalyst

Answer 1

Look carefully at each step and notice that the HClO formed in step (1) is used up in step (2) making it an intermediate. Also notice that the OH- formed in step (1) is used in step (3) and that H₂O(l) is generated in step (3). Since H₂O(l) is used in step (1) and generated in step (3), it satisfies the definition of a catalyst, namely that is NOT used up or consumed during the reaction. As a side, you can also state that HIO is an intermediate as it is generated in step (2) and used in step (3).

Also, thought not asked for in this question, you should note that adding all steps together and canceling intermediates and catalysts, gives you the overall reaction:

ClO^- + I^- ===> Cl^- + IO^-