Question

The number of ${OH}^{-}$ ions in one mL solution of $pH=3$ is $6.023\times {10}^{a}M$. The value of $a$ is:

Answer 1

$pOH=14-pH=14-3=11$

$-log\left[O{H}^{-}\right]=11;\left[O{H}^{-}\right]={10}^{-11}$

So no of ions in 1 ml is $={10}^{-11}\times {10}^{-3}\times N_A={10}^{-14}\times N_A=6.023\times {10}^9$

So value of a is 9.