Question

$pH$ of a solution produced when aqueous solution of $pH=6$ is mixed with an equal volume of an aqueous solution of $pH=3$ is about:

• A. $3.3$
• B. $4.3$
• C. $4.5$
• D. $4.0$

Answer 1

Answer: (A)

The $pH$ of solution is negative logarithm of hydrogen ion concentration.
$pH=-log\left[H^{+}\right]$
Hence, $\left[H^{+}\right]={10}^{-pH}$
$pH=3$ and $pH=6$ corresponds to hydrogen ion concentrations of $0.001M$ and $0.000001M$ respectively.
Assuming $1L$ of each solution is mixed,
the concentration of resulting solution is $\frac{0.001M+0.000001M}{2}=0.0005M$.
$pH=-log\left[H^{+}\right]=-log\left(0.0005\right)=3.3$