Question

The $pH$ value of $HCl({10}^{-12}M)$ is

• A. $-7$
• B. $7$
• C. $12$
• D. $-12$

Answer 1

Answer: (B)

We know that ${10}^{-12}M$ solution of $HCl$ is very dilute. So concentration of $H$ ions due to self-ionisation of water cannot be neglected. Therefore, ${[H^{+}]}_{total}=H^{+}[fromHCl+water]$ $-\log [1.00001\times {10}^{-7}]=7.$ We also know that $pH=-\log [H^{+}]$ $=-\log [1.00001\times {10}^{-7}]=7$