Question

Which of the following aqueous solutions, when added to $100ml$ of $0.1MHCl\left(aq\right)$ will cause no change in its $pH$? Assume volumes to be additive.

• A. $100ml$ distilled water
• B. $100ml$ of $0.1MHN{O}_3$
• C. $50ml$ of $0.2MHCl$
• D. $100ml$ of $0.1MAgN{O}_3$

Answer 1

The correct option is B $100ml$ of $0.1MHN{O}_3$

$M$ moles of $HCl=0.1\times 100=10$

The solution added should be such that,

$\left[H^{+}\right]=0.1M$ reamians the same.

When $100ml$ of $0.1M$ $HN{O}_3$ is added,

total $m$ moles of $H^{+}=10+100\times 0.1=20$

Total volume $=200ml$

$\therefore \left[H^{+}\right]final=\frac{20}{200}=0.1M$

Hence $pH$ will remain the same.