Question

$5.0\, g$ of sodium hydroxide (molar mass $40\, g \,mol^{-1}$) is dissolved in little quantity of water and the solution is diluted up to $100\, ml$. What is the molarity of the resulting solution ?

• A. $0.1\, mol\, dm^{ - 3}$
• B. $1.0\, mol\, dm^{ - 3}$
• C. $0.125\, mol\, dm^{ - 3}$
• D. $1.25\, mol\, dm^{ - 3}$

Answer 1

Answer: (D)

Given, $W$ (mass of solute) $=5.0 g$

$m$ (molar mass of solute) $=40 g mol ^{-1}$

Volume $=100 mL$

Molarity is given as,

$M =\frac{\text { Moles of solute }}{\text { Volume of solution (in L) }}$

$M =\frac{W \times 1000}{m \times \text { Volume of solution (in } mL )}$

$M =\frac{5.0 g \times 1000}{40 \times 100}$

$=1.25\, mol \,dm ^{-3}$