# Rate Law Problem

cvc121
1. Homework Statement

Due to formatting problems, I have attached the question below.

The attempt at the solution:
I am not sure how to deal with the hydroxide ion since it is written above the arrow. I believe that this signifies a species not included in the overall reaction but is necessary for the reaction to proceed? An intermediate maybe? Therefore, should the hydroxide ion be in the rate law?

Using trials 1 and 2 where the concentration of OCI- and OH- is held constant, I have determined that the reaction is first order with respect to [I-].

However, there are no trials where the concentration of OCI- changes and the other two are held constant.

I am not sure how to proceed from here. Can anyone provide some guidance. Thanks. All help is very much appreciated.

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## Answers and Replies

Gold Member
I am not sure how to deal with the hydroxide ion since it is written above the arrow. I believe that this signifies a species not included in the overall reaction but is necessary for the reaction to proceed? An intermediate maybe? Therefore, should the hydroxide ion be in the rate law?
Is there any data from which you can deduce the answer?

Using trials 1 and 2 where the concentration of OCI- and OH- is held constant, I have determined that the reaction is first order with respect to [I-].
This looks correct to me.

However, there are no trials where the concentration of OCI- changes and the other two are held constant.

I am not sure how to proceed from here. Can anyone provide some guidance. Thanks. All help is very much appreciated.

If you find out how the rate depends on [I-] and [OH-], you should be able to calculate how the rate depends on [OCl-] even if the all three concentrations are changing.

cvc121
Thank you for your response.

Using trials 4 and 2, I have determined that the reaction order is -1 with respect to the hydroxide ion.

Therefore, I have determined the reaction to be first order with respect to [OCI-] using trials 2 and 3, for instance.

So rate law would be rate = k [I-][OCI-] / [OH-]?

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Homework Helper
Gold Member
Something written above the arrow for the reaction brackets (which is balanced without it) usually does the signify a catalyst. Whether the data says it really is one does not exactly hit you in the eye!

You could try looking at ratios of reactant concentrations And corresponding ratios of rates, and factoring in the one law that you do know to see whether that gives you anything. I haven't tried it.

Unless it is important for some external reason, this data does not seem to be worth wasting a lot of time on.

Gold Member
Thank you for your response.

Using trials 4 and 2, I have determined that the reaction order is -1 with respect to the hydroxide ion.

Therefore, I have determined the reaction to be first order with respect to [OCI-] using trials 2 and 3, for instance.

So rate law would be rate = k [I-][OCI-] / [OH-]?
That looks correct to me. Good job!