Question

The pH of a solution obtained by mixing $50ml$ of $0.4M$ $HCl$ with $50ml$ of $0.2M$ $NaOH$ is:

• A. $-\log 2$
• B. $-\log 2\times {10}^1$
• C. $1.0$
• D. $2.0$

Answer 1

Answer: (C)

$1.0$

Millimole of $HCl=50\times 0.4=20$

Millimoles of $NaOH=50\times 0.2=10$

Millimoles of $HCl$ left $=20-10=10$

Volume of solution $=100ml$

$\therefore$ Moles of $HCl$ per litre $=\frac{10\times {10}^{-3}\times 1000}{100}={10}^{-1}M$

$pH=-\log \left({10}^{-1}\right)=1$