Question

What is the volume of water that must be added to a mixture of 250 ml of 6M $HCl$ solution and 650 ml of 3M $HCl$ solution to obtain a 3M solution?

• A. 75ml
• B. 150ml
• C. 300ml
• D. 250ml

Answer 1

The correct option is D 250ml

When two solutions are mixed together to form a solution, we apply the formula:

$M_1{V}_1+M_2{V}_2=M\times V$, where $M_1,M_2,V_1,V_2$ are the molarity and volume of the solutions being mixed, and M and V are the molarity and volume of the final solution.

$250\times 6+650\times 3=3\times V$
$⟹V=1150ml$

The total volume of the solution is 1150 ml. The volume present initially is $(250+650)=900$ ml solution. We need to add 250 ml of water to obtain a 3 M solution.

Hence, the correct option is $D$