Question

For converting a solution of $\text{100 mL KCl}$ of 0.4 M concentration into a solution of $\text{KCl}\text{0}\text{.05}\text{M}$ concentration. The quantity of water added is

• A. 900 mL
• B. 700 mL
• C. 500 mL
• D. 300 mL

Answer 1

Answer: (B)

Key Idea: First calculate the total volume of solution by using formula ${\text{M}}_1{V}_1=M_2{V}_2.$ Then subtract original volume of $\text{KCl}$ solution (= 100 mL) from calculated volume to get the amount of water added. Given ${\text{M}}_1=0.4M,M_2=0.05M$ $V_1=100mL,V_2=?$ $M_1{V}_1=M_2{V}_2$ $0.4\times 100=0.05\times V_2$ or $V_2=\frac{0.4\times 100}{0.05}$ $\text{=}\text{800}\text{mL}$ Volume of water to be added $=V_2-V_1$ $=800-100$ = 700 mL