Question

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

• A. between 7 and 8
• B. between 5 and 6
• C. between 6 and 7
• D. between 10 and 11
• E. between 9 and 10

Answer 1

The correct option is A between 7 and 8

Concentration of diluted base is $\left[{OH}^{-}\right]={10}^{-6}/100={10}^{-8}$

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

$\left[{OH}^{-}\right]={10}^{-8}+{10}^{-7}=11\times {10}^{-8}$

$pOH=-\log \left[{OH}^{-}\right]$

$pOH=-\log [11\times {10}^{-8}]=6.958$

$pH$ is $14-pOH=14-6.985=7.0414$

lies between 7 and 8.