Question

We have 100 mL of 0.1 M $KCl$ solution. To make it $0.2$ M:

• A. evaporate 50mL water
• B. evaporate 50mL solution
• C. add 0.1 mol $KCl$
• D. add 0.01 mol $KCl$

Answer 1

Answer: (A), (B), (D)

The correct options are
A evaporate 50mL water
B evaporate 50mL solution
D add 0.01 mol $KCl$

$100ml\times 0.1M=xml\times 0.2M$
$x=\frac{100mL\times 0.1M}{0.2M}=50mL$

Hence to make the required solution, the total volume of the solution should be reduced to 50 mL.
This can be done by evaporating 50 mL of water or solution.

Also $Molarity=\frac{\text{Number of moles of solute}}{\text{Volume of solution}}$

Substitute values in the above expression.

$Molarity=\frac{n}{0.1L}=0.2M$

Hence, $n=0.02M$
Thus, the number of moles should be increased from $0.01$ to $0.02$ by addition of $0.01$ moles of $KCl$.