Question

The amount of sodium hydroxide (in g) required to make 100 mL of its 0.5 M aqueous solution is

• A.
  5 g
• B.
  2 g
• C.
  10 g
• D.
  2.5 g

Answer 1

The correct option is B

2 g
$\text{Molarity}=\frac{\text{Number of moles of solute}}{\text{Volume of solution (in mL)}}\times 10000.5=\frac{\text{Number of moles of NaOH}}{100}\times 1000\text{Number of moles of NaOH}=\frac{0.5\times 100}{1000}\text{Number of moles of NaOH = 0.05}\text{Molar mass of NaOH}=40gmo{l}^{-1}\text{Number of moles}=\frac{\text{Mass}}{\text{Molar mass}}0.05=\frac{Mass}{40}\text{Mass of NaOH}=0.05mol\times 40gmo{l}^{-1}=2g$

Hence, the correct answer is option (b).