Question

What volume of water must be added to a solution of 250 mL of a 6 M HCl solution and 650 mL of a 3 M HCl solution to obtain a 3 M resultant solution?

• A. 60 mL
• B. 350 mL
• C. 250 mL
• D. 500 mL

Answer 1

The correct option is C 250 mL

When two solutions are mixed to form a solution,
$M_1{V}_1+M_2{V}_2=M\times V$
Where $M_1$ and $M_2$ are the concentrations of the given HCl solutions and $V_1$ and $V_2$ are their respective volumes.
$M_1=6M,M_2=3M,V_1=250mL,V_2=650$ mL
M and V are the molarity and volume of the final solution, respectively.
$(250\times 6)+(650\times 3)=3\times V$
$\Rightarrow V=1150$ mL
$V_1+V_2=(250+650)$ mL = 900 mL
Therefore, 1150 – 900 = 250 mL of water should be added to obtain a 3 M resultant solution.