Question

If Half life of a substance is 36 minutes. Find amount left after $2hrs$, if initial amount is $10g$ ?

• A. 1 g
• B. 2 g
• C. 3 g
• D. 4 g

Answer 1

Answer: (A)

$t_{1/2}=\frac{0.693}{k}$

$k=\frac{0.693}{t_{1/2}}=\frac{0.693}{36}$

$k=\frac{2.303}{t}log\frac{a}{a-x}$

$\frac{0.693}{35}=\frac{2.303}{2\times 60}log\frac{a}{a-x}$

$\frac{0.693\times 2\times 60}{36\times 2.303}=log\frac{a}{a-x}$

$1.0=log\frac{a}{a-x}$

$10=\frac{a}{a-x}$ a = 10g (given)

$a-x=\frac{10}{10}$ = 1.0 g