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}}=0.4\,M,\,{{M}_{2}}=0.05\,M $ $ {{V}_{1}}=100\,mL,\,{{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