Question

How many moles of $NaOH$ must be added to $200ml$ of $0.1M$ solution of $H{NO}_3$ to get a solution having pH value $2$? (considering $NaOH$ in solid state)

• A. $0.08$
• B. $0.018$
• C. $0.011$
• D. $0.01$

Answer 1

The correct option is B $0.018$

At $0.1MHN{O}_3$ $pH=$ $-log\left[{10}^{-1}\right]=1$

mole of $HN{O}_3$ = $0.1M\times 0.2L=0.02mole$

For $pH=2$ $H^{+}$ ion concentration must be = ${10}^{-2}$

mole of $HN{O}_3$ = $0.01M\times 0.2L=0.002mole$

$NaOH+HN{O}_3\to H_{2}O+NaN{O}_3$ to make pH =2, we have to neutralize $0.02-0.002$ mole hydronium ions. Thus $0.018$ mole of $NaOH$ will be added in solution.