Question

What is the molarity of a solution prepared by dissolving 4 g of NaOH in 250 mL of solution? (Molar mass of NaOH = 40 g/mol)

• A. 0.2 M
• B. 0.4 M
• C. 0.8 M
• D. 1.6 M
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Hint:

To calculate molarity, use \( M = \frac{\text{moles of solute}}{\text{volume in liters}} \), ensuring volume is converted from mL to L (divide by 1000).

Answer 1

The Correct Option is B

Molarity (M) is defined as: \[ \text{Molarity} = \frac{\text{moles of solute}}{\text{volume of solution (in liters)}} \] Calculate moles of NaOH: \[ \text{Moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{4}{40} = 0.1 \, \text{mol} \] Volume of solution = 250 mL = 0.25 L. Thus: \[ \text{Molarity} = \frac{0.1}{0.25} = 0.4 \, \text{M} \] The molarity of the solution is: \[ {0.4} \]