Question

To 20 mL of 1.5 M $HCl$ solution, 30 mL of water is added and to this resultant solution again 75 mL of 0.4 M HCl is added. The molarity of the resultant solution is:

• A. 0.40 M
• B. 2.10 M
• C. 0.48 M
• D. 5.5 M

Answer 1

The correct option is C 0.48 M

In the first case,
$M_1{V}_1=M_2{V}_2$
here, $M_1=1.5M;V_1=20mL;V_2=50mL$
So $M_2=\frac{1.5\times 20}{50}=0.6M$
Now, to this 0.6 M of 50 mL $HCl$ solution, 75 mL of 0.4 M $HCl$ is added.
Using,
$M_3=\frac{M_1{V}_1+M_2{V}_2}{V_3}$
where $V_3=50+75=125$ mL
$M_3=\frac{(0.6\times 50)+(75\times 0.4)}{125}{M}_3=0.48M$