Question

The mechanism of a chemical reaction is given below.

(CH3)3CCl → (CH3)3C+ + Cl– (slow)

(CH3)3C+ + OH– → (CH3)3COH (fast)

Which of the following statements concerning the reaction is/are CORRECT?

1. The overall balanced reaction is: (CH3)3CCl + OH– → (CH3)3COH + Cl–

2. Hydroxide ion is a reaction intermediate.

3. The following rate law is consistent with the mechanism: rate = k[(CH3)3CCl][OH–].

Answer 1

1) The balanced reaction is (CH₃)₃CCl + OH ^- (CH₃)₃COH + Cl ^-

ANSWER : Correct

Slow: (CH₃)₃CCl (CH₃)₃C ⁺ + Cl ^-

Fast: (CH₃)₃C ⁺ + OH ^- (CH₃)₃COH

Overall : (CH₃)₃CCl + OH ^-   (CH₃)₃COH + Cl ^-

2) Hydroxide ion is a intermediate.

ANSWER : INCORRECT

Intermediate is a species produced in one step of reaction and it is consumed in another step of reaction.

In above reaction, (CH₃)₃C ⁺ is produced in first step of reaction and it is consumed in second step of reaction. Hence , intermediate is  (CH₃)₃C ⁺

Hydroxide ion is not a intermediate.

3) The following rate law is consistent with mechanism Rate = k [(CH₃)₃CCl ] [ OH ^-]

ANSWER : INCORRECT

In multi step reaction, rate of reaction depends on slow step of reaction. In this multi step reaction, first step is slow step.

Slow : (CH₃)₃CCl (CH₃)₃C ⁺ + Cl ^-

For above reaction, we can write rate of reaction = k [(CH₃)₃CCl] .

Rate of this multi step reaction will depend on concentration of (CH₃)₃CCl and not on OH ^- . Hence, rate law is

Rate = k [(CH₃)₃CCl] .