Rates, whats wrong with my working?

[geffman1]

hey guys I've got a question.

We examine the conversion of cyclopropane to propene, a first order process. If we begin with 0.0200 M cyclopropane and find that after 168 s the concentration of propene is 0.00286 M, what is the rate constant, k, at this temperature?

My working:
In[A]-In[A]=-kt
(In0.00286-In0.0200)/168=-k
therefor k=0.011576 however correct answer is 9.19x10-4

anyhelp would be good. thanks

 

[vertciel]

Hello there,

I get the same answer in mol/(L x s) as you. Could you verify that the correct answer is given in the same units?

Thanks.

 

[geffman1]

C. 9.19 x 10-4/s here's the answer out exercise, maybe they just made a mistake, are we using the right formula? thanks for the reply

 

[vertciel]

You're welcome.

Unfortunately, I still have not found a different answer. Is this textbook a recognised, leading one in chemistry? If not, then the answer key may be erroneous.