Question

What will be the molarity of a solution, which contains 5.85 g of NaCl (s) per 500 mL?

• A. $20mol{L}^{-1}$
• B. $2mol{L}^{-1}$
• C. $4mol{L}^{-1}$
• D. $0.2mol{L}^{-1}$

Answer 1

The correct option is D $0.2mol{L}^{-1}$

Calculating the number of moles of solute


Mass of solute (Nacl) = 5.85 g
Molar mass of solute (Nacl) = 58.5 g/mol

$\therefore$ Number of moles of solute (Nacl) =
$\frac{\text{Mass of solute}}{\text{Molar mass of solute(Nacl)}}=\frac{5.85}{58.5}=0.1mol$

Molarity

To find molarity, formula used is:
Volume of the solution = 500 mL = 0.5 L

Molarity = $\frac{\text{number of moles of solute}}{\text{Volume of solution (in L)}}$

$=\frac{0.1mol}{0.5L}=0.2mol{L}^{-1}$

Thus, molarity of the given solution is $0.2mol{L}^{-1}$