Question

The number of hydroxyl ions in $100mL$ of a solution having $pH10$ is

• A. $1\times 10^4$
• B. $3.012\times 10^4$
• C. $6.02\times 10^{18}$
• D. $6.023\times 10^{19}$

Answer 1

Answer: (C)

Given, $pH=10$
$\therefore \left[H^{+}\right]=1\times 10^{-pH}=1\times 10^{-10}mol/L$
$\therefore \left[O{H}^{-}\right]=\frac{1\times 10^{-14}}{1\times 10^{-10}}=1\times 10^{-4}mol/L$
$\because$ The number of hydroxyl ions present in $1mol=6.023\times 10^{23}$
$\therefore$ The number of hydroxyl ions in
$1\times 10^{-4}mol/L=6.023\times 10^{23}\times 10^{-4}/L$
$=6.023\times 10^{19}/L$
$\because$ In $1000mL$ number of hydroxyl ions
$=6.023\times 10^{19}$
$\therefore$ In $100mL$ number of hydroxyl ions
$=\frac{6.023\times 10^{19}\times 100}{1000}$
$=6.023\times 10^{18}.$