Question

Number of hydrogen ions present in 10 millionth part of $1.33{cm}^3$ of pure water at ${25}^{o}C$ is:

• A. $6.023$ million
• B. $60$ million
• C. $8.01$ million
• D. $80.23$ million

Answer 1

The correct option is C $8.01$ million

$10$ million $={10}^{-7}$

$\therefore$ $10$ millionth part of $1.33{cm}^3=1.33\times {10}^{-7}{cm}^3=1.33\times {10}^{-7}mL$

For pure water, $\left[H^{+}\right]={10}^{-7}mol/L$

$\Rightarrow$ $1L$ water contains $\left[H^{+}\right]={10}^{-7}mol$

or $1mL$ water contains $\left[H^{+}\right]=\frac{{10}^{-7}}{1000}={10}^{-10}mol$

or $10$ millionth part of $1.33{cm}^3$ water contains

$\left[H^{+}\right]=1.33\times {10}^{-7}\times {10}^{-10}mol=1.33\times {10}^{-17}mol$

$\therefore$ Number of $H^{+}$ ions $=1.33\times {10}^{-17}\times N_A$

$=1.33\times {10}^{-7}\times 6.022\times {10}^{23}$

$=8.009\times {10}^6=8.01$ million