Question

The amount of lactic acid, $H{C}_3{H}_5{O}_3$, produced in a sample of muscle tissue was analysed by reaction with hydroxide ion. Hydroxide ion was produced in the sample mixture by electrolysis. The cathode reaction was,
$2H_{2}O\left(l\right)+2e^{-}\to H_2\left(g\right)+2O{H}^{-}(aq.)$
Hydroxide ion reacts with lactic acid as soon as it is produced. The end point of the reaction is detected with an acid-base indicator. It required $115$ seconds for a current of $15.6mA$ to reach end point. How many grams of lactic acid (a monoprotic acid) were present in the sample?

Answer 1

No. of moles of lactic acid $=$ No. of mole of $O{H}^{-}$ used
$=$ No. of faraday used in electrolysis
Number of faraday used $=\frac{I\times t}{96500}=\frac{15.6\times {10}^{-3}\times 115}{96500}$
$=1.86\times {10}^{-5}$
Mass of lactic acid $=$ Number of moles $\times$ Molecular mass
$=1.86\times {10}^{-5}\times 90=1.674\times {10}^{-3}g$.