Question

Which of the following should be done in order to prepare $0.40$ M $NaCl$ starting with $100$ ml of $0.30$ M NaCl?

[Mol. wt. of $NaCl$$=58.5$]

• A. Add $0.585$ g NaCl
• B. Add $20$ ml water
• C. Add $0.010$ ml NaCl
• D. Evaporate $10$ ml water

Answer 1

Answer: (A)

Add $0.585$ g NaCl

$M=\frac{n}{VinL}$

Using above expression, we cqan say that,

$100$ ml of $0.30$ M$=0.3\times \frac{100}{1000}=0.03$ mole of NaCl

Similarly, $100$ ml of $0.40$ M $=0.04$ mol of NaCl

Moles of NaCl to be added $=0.04-0.03$ $=0.01$ mol $=0.01\times 58.5$ g $=0.585$ g

Hence, the correct option is $A$