Question

Equal volumes of $0.200\, M \,HCl$ and $0.400\, M\, KOH$ are mixed. The concentration of the principal ions in the resulting solution are

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

Answer 1

Answer: (C)

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