Question

The hydrogen ion concentration of three monoprotic acids $A,B$ and $C$ are $1\times {10}^{-5}\text{mol/L},1\times {10}^{-3}\text{mol/L}$ and $1\times {10}^{-2}\text{mol/L}$ respectively.
The correct order of their acidic strength is:

• A. $A>B>C$
• B. $B>C>A$
• C. $C>B>A$
• D. $A>C>B$

Answer 1

The correct option is C $C>B>A$

$pH=-\log \left[H^{+}\right]$
$pH$ of acid $A$ $=-\log \left[H^{+}\right]=-\log \left[{10}^{-5}\right]=5$
$pH$ of acid $B$ $=-\log \left[H^{+}\right]=-\log \left[{10}^{-3}\right]=3$
$pH$ of acid $C$ $=-\log \left[H^{+}\right]=-\log \left[{10}^{-2}\right]=2$
Since lower the value of $pH$, higher is the acidic strength.
$\therefore C>B>A$