Question

The deactivation of ascorbic acid follows first order kinetics. $25$ mL sample of juice is kept for $2$ months and after $2$ months, on titration with same $KI{O}_3$ in presence of $1MHCl$ solution requires $0.5$ mL of $KI{O}_3$ solution. The average life of fruit juice is :

• A. $60$ days
• B. $54.6$ days
• C. $86.5$ days
• D. $120$ days

Answer 1

Answer: (B)

$54.6$ days

$166$ mL sample of fresh juice requires $10$ mL of $KI{O}_3$.
$25$ mL of sample of fresh juice will require $=\frac{25}{166}\times 10=1.5$ mL of $KI{O}_3$.
After $2$ months, $25$ mL of sample of fresh juice requires $0.5$ mL of $KI{O}_3$.
Hence, $k=\frac{2.303}{t}log\frac{a}{a-x}$ for first order kinetics.
$k=\frac{2.303}{60}log\frac{1.5}{0.5}=0.0183$
The average life is $\frac{1}{k}=\frac{1}{0.0183}=54.6$ days.