The reaction `[Co (NH_(3))_(5)Br]^(2) + (H_(2)O) rarr [Co(NH_(3))_(5)(H_(2)O)]^(3+) + Br^(-)` is followed by measuring a property of the solution known as the optical density of the solution which may be taken to be linearly related to the concentration of the reactant. The values of optical density are `0.80, 0.35` and `0.20` at the end 0f `20` minutes, `40` minutes and infinite time after the start of the reaction which is first order. Calculate the rate constant.

Options

A. `6.93 xx 10^(-3) "min"^(-1)`
B. `3.51 xx 10^(-3) "min"^(-1)`
C. `6.93 xx 10^(-2) "min"^(-1)`
D. `3.51 xx 10^(-3) "min"^(-1)`

Answer

C

Explanation

`(2.303)/((40 - 20))"log"((0.80 - 020))/((0.35 - 0.20)) = 6.93 xx 10^(-2)`