Question

An organic compound was used with sodium metal and extracted with distilled water. On adding freshly prepared $FeS{O}_4$ solution followed by the addition of $FeC{l}_3$ and dil. $HCl$ used greenish-blue solution. $0.30$ g of the organic compound after kjeldahlisation evolved a gas (X), which was passed on $100$ ml of $0.1$ M $H_{2}S{O}_4$. The excess of acid required $20$ ml of $0.5$ M NaOH for neutralisation. The amount of acid left after neutralisation with base is:

• A. $10$ ml
• B. $90$ ml
• C. $50$ ml
• D. $80$ ml

Answer 1

The correct option is C $50$ ml

As following reaction suggests:
$H2SO4+2NaOH------------->Na2SO4+2H2O$
20 mL (0.5M)
So, 20 mL (0.5 M) of NaOH is required to neutralise 20 mL (0.25M) H2SO4.
As given, molarilty of $H2SO4=100mL\left(0.1M\right)$.
So, $\left(0.25/1000\right)\ast 20=\left(0.1/1000\right)\ast x$
x = volume required of 0.1 M acid
$x=\left(0.25/0.1\right)\ast 20=\left(25/10\right)\ast 20$ = $50mL$
So, The amount of acid left after neutralisation with base is $50mL$.