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

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

JIPMERJIPMER 2019

Solution:


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

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

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

$\frac{0.693}{35}=\frac{2.303}{2\times60}log \frac{a}{a-x}$

$\frac{0.693\times2\times60}{36\times2.303}=log \frac{a}{a-x}$

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

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

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