Question

Hydrolysis of DDT is a first order reaction, its half life is $10years$. Time to hydrolyse $10g$ DDT to half is:

• A. $100years$
• B. $50years$
• C. $5years$
• D. $10years$

Answer 1

Answer: (D)

$10years$

$K=\frac{0.693}{t_{1/2}}=\frac{0.693}{10years}$

If initial concentration $a=10$ gm and final concentration

$x=\frac{a}{2}=5gm$

then, $t=\frac{2.303}{K}\log \frac{a}{a-x}=\frac{2.303}{.693}\times 10\times \log \frac{10}{5}$

$=\frac{2.303\times 10\times \log 2}{.693}=\frac{2.303\times 10\times 0.301}{0.693}=10years.$