Question

A stock solution of $10$ $M$ $NaOH$ was used to prepare $2$ L of $0.5$ $M$ $NaOH$. How many millilitres of sodium hydroxide stock solution ?

• A. $10$ ml
• B. $100$ ml
• C. $1000$ ml
• D. $200$ ml
• E. $2000$ ml

Answer 1

The correct option is B $100$ ml

$MV=M^{\prime }{V}^{\prime }$
M is the molarity of stock solution (10 M).
V is the volume (in L) of stock solution.
M' is the molarity of diluted solution ( 0.5 M).
V' is the volume of diluted solution (2 L).
Hence,
$10\times V=0.5\times 2$
$V=0.1$ L
Also 1 L $=$ 1000 ml
Hence, $V=0.1\times 1000$ ml $=100$ ml.
Hence, 100 ml of the stock solution are required.