Question

The volume of water that must be added to a mixture of 250 mL of 0.6 M $HCl$ and 750 mL of 0.2 M $HCl$ to obtain a 0.25 M solution is:

• A. 200 mL
• B. 250 mL
• C. 400 mL
• D. 300 mL

Answer 1

The correct option is A 200 mL

Let the amount of water to be added is $x$ mL.
Conserving the total moles before and after mixing:
$M_1{V}_1+M_2{V}_2=MV$
where $M_2$ and $V_2$ are the molarity and volume of 0.6 M solution.
$M_1$ and $V_1$ are the molarity and volume of 0.2 M solution and $M$ and $V$ are the molarity and volume of the final mixture.
So,
$0.25\times (1000+x)=(0.6\times 250)+(0.2\times 750)$
On solving, $x=200$ mL
Therefore, amount of water added is 200 mL.