Question regarding rates for reaction..please help

Question

The following set of data was obtained by the method of initial rates for the reaction:

(H3C)3CBr OH- -> (H3C)3COH Br-

What is the order of reaction with respect to ion, OH-?

[(H3C)3CBr] (M) ..... [OH-] (M) .... Initial Rate (M/s)

....0.25..................... 0.25 ...............1.1 x 10^-4

....0.50..................... 0.25 ...............2.2 x 10^-4

....0.50..................... 0.50 ...............2.2 x 10^-4

A)zero B)first C)second D)none of these

please explain the answer.. thank you.

Answer 1

The easiest way to do this is to look at where the [OH-] doubles which is the 2nd to 3rd row from 0.25 to 0.50. If you look at the [(H3C)3CBr)] you can see that from the 2nd to 3rd row, the concentration remains constant which is what we want. Now look at the corresponding Initial Rates and from 2nd to 3rd row the rate increased by a factor of 1. So you can write out a simple equation like this:

2^x = 1

Solve the equation:

x = 0

Since anything to the zero power equals one.

So your answer is A) zero

with respect to [OH-]

This makes sense because increasing the concentration of [OH-] while the other reactant remained constant did not affect the initial rate of reaction at all.