Question

Calculate the molarity of the resultant solution in each of the following cases:
i. 200 mL of 1 M HCl + 300 mL water
ii. 200 mL of 1 M HCl + 100 mL of 0.5 M HCl

• A. $0.4M,\frac{5}{6}M$
• B. 0.4 M, 0.5 M
• C. $0.2M,\frac{5}{6}M$
• D. 0.5 M, 0.5 M

Answer 1

The correct option is A $0.4M,\frac{5}{6}M$

(i) $M_R\times V_R=M_1\times V_1$
Where $M_R$ is the molarity and $V_R$ is the volume of the resultant solution and $M_1$ and $V_1$ is the molarity and volume of the HCl solution, respectively.
Molarity of the resultant solution, $M_R=\frac{M_1\times V_1}{V_R}=\frac{1\times 200}{500}=0.4M$
(Where $V_R$ is the volume of the resultant solution = (200 + 300) = 500 mL)
(ii). $M_1{V}_1+M_2{V}_2=M_R{V}_R$
Volume of the resultant solution, $V_R=V_1+V_2$
Molarity of the resultant solution, $M_R=\frac{M_1{V}_1+M_2{V}_2}{V_R}=\frac{(1\times 200)+(0.5\times 100)}{300}=\frac{5}{6}M$