Question

Equal volumes of $0.200MHCl$ and $0.400MKOH$ are mixed. The concentration of the principal ions in the resulting solution are

• A. $\left[K^{+}\right]=0.400M,\left[C{l}^{-}\right]=0.200M,\left[H^{+}\right]=0.200M$
• B. $\left[K^{+}\right]=0.200M,\left[C{l}^{-}\right]=0.200M,\left[O{H}^{-}\right]=0.100M$
• C. $\left[K^{+}\right]=0.200M,\left[C{l}^{-}\right]=0.100M,\left[O{H}^{-}\right]=0.100M$
• D. $\left[K^{+}\right]=0.200M,\left[C{l}^{-}\right]=0.100M,\left[O{H}^{-}\right]=0.200M$

Answer 1

Answer: (C)

$K^{+}$and $C{l}^{-}$remain unchanged but due to dilution (in equal volumes), molar concentration of each is halved
$\left[C{l}^{-}\right]=0.1M$
$\left[K^{+}\right]=0.2M$
Also, $\left[O{H}^{-}\right]>\left[H^{+}\right]$, mixture is basic
${\left[O{H}^{-}\right]}_{\text{mix }}=\frac{0.4-0.2}{2}=0.1M$