A) 900 mL
B) 700 mL
C) 500 mL
D) 300 mL
Correct Answer: B
Solution :
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
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