Rate equation for first order reaction is as follows:
Here, k is rate constant of the reaction, t is time of the reaction, is initial concentration and
is concentration at time t.
The rate constant of the reaction is .
(a) Let the initial concentration be 100, If 90% of the chemical is destroyed, the chemical present at time t will be 100-90=10, on putting the values,
Thus, time required to destroy 90% of the chemical is 23.03 days.
(b) Let the initial concentration be 100, If 99% of the chemical is destroyed, the chemical present at time t will be 100-99=1, on putting the values,
Thus, time required to destroy 99% of the chemical is 46.06 days.
(c) Let the initial concentration be 100, If 99.9% of the chemical is destroyed, the chemical present at time t will be 100-99.9=0.1, on putting the values,
Thus, time required to destroy 99.9% of the chemical is 69.09 days.