Question

$6.90$ M solution of $KOH$ in water contains $30$% by mass of $KOH$. What is the density of solution?

• A. $1.155$ g/mL
• B. $1.258$ g/mL
• C. $1.288$ g/mL
• D. $1.358$ g/mL

Answer 1

Answer: (C)

$1.288$ g/mL

The molar mass of $KOH$ is $56.1$ g/mol.

$6.90$ M $KOH$ solution corresponds to $6.90$ moles ( or

$6.90\times 56.1=387.09$ g) of $KOH$ in $1$ L of solution.

The solution contains $30$% by mass of $KOH$.

Thus, the mass of the solution is $387.09\times \frac{100}{30}=1288$ g.

The density of the solution is $\frac{Mass}{Volume}=\frac{1288}{1000}=1.288$ g/mL.

So, the correct option is $C$