Question
Calculate the pH of 0.01 M HCl solution.

Answer

HCl is a strong acid, hence it ionises completely.
$\begin{array}{ccc} HCl ( aq ) \longrightarrow  &H ^{+}( aq ) & + Cl ^{-}( aq ) \\ 0.01 M & 0.01 M & 0.01 M \end{array}$
$\begin{array}{l}\therefore\left[ H ^{+}( aq )\right]=0.01 M =1 \times 10^{-2} M \\ \text { Now, } pH =-\log _{10}\left[ H ^{+}( aq )\right]\end{array}$
$=-\log _{10}\left[1 \times 10^{-2}\right]=-[\overline{2} \cdot 0000]=2$

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