Question

$10^{-6}MNaOH$ is diluted $100$ times. The $pH$ of the diluted base is

• A. between 6 and 7
• B. between 10 and 11
• C. between 7 and 8
• D. between 5 and 6

Answer 1

Answer: (C)

$\left[O{H}^{-}\right]$ in the diluted base $=\frac{10^{-6}}{10^2}=10^{-8}$

Total $\left[O{H}^{-}\right]=10^{-8}+\left[O{H}^{-}\right]$ of water

$=\left(10^{-8}+10^{-7}\right)M$

$=10^{-8}[1+10]M$

$=11\times 10^{-8}M$

$pOH=-\log 11\times 10^{-8}$

$=-\log 11+8\log 10$

$=6.9586$

$pH=14-6.9586$

$=7.0414$