Question

What is the volume of methanol needed for making $2\,L$ of $0.4\,M$ solution? (Density of methanol $= 0.64\,kg\,L^{-1}$ and molar mass $= 32\,g\,mol^{-1}$)

• A. $20\,mL$
• B. $4\,mL$
• C. $40\,mL$
• D. $10\,mL$
• E. $80\,mL$

Hint:

Convert density into $g/L$ for easier calculation.

Answer 1

The Correct Option is C

Concept:
• Molarity: \[ M = \frac{n}{V} \]

Step 1: Moles required
\[ n = 0.4 \times 2 = 0.8\,mol \]

Step 2: Mass of methanol
\[ m = 0.8 \times 32 = 25.6\,g \]

Step 3: Volume using density
\[ \rho = 0.64\,kg/L = 640\,g/L \] \[ V = \frac{25.6}{640} = 0.04\,L = 40\,mL \] Final Conclusion:
Option (C)