Question

How long will it take for 85% of the sample to decompose ?

Answer 1

The sample is 85% decomposed.
$a=100$ and $a-x=100-85=15$
The expression for the relationship between the rate constant k, the time t, the initial concentration a and final concentration a-x is as given below.
$t=\frac{2.303}{k}log\frac{a}{a-x}$
Substitute values in the above expression.
$t=\frac{2.303}{1.06\times {10}^{-3}}log\frac{100}{15}=1790min$.