Calculate the solubility (mol dm⁻³) of 40 g of CuSO₄ dissolved in 100 g of water at 120 °C. [Cu = 64, S = 32, O = 16]

Step 1: Find molar mass of CuSO₄

• Cu = 64
• S = 32
• O₄ = 16 × 4 = 64

Total = 64 + 32 + 64 = 160 g/mol

Step 2: Calculate moles of CuSO₄

\[ \text{Moles} = \frac{\text{Mass}}{\text{Molar mass}} = \frac{40}{160} = 0.25 \; \text{mol} \]

Step 3: Convert mass of solvent (water) to dm³

• Mass of water = 100 g
• Density of water ≈ 1 g/cm³, so 100 g ≈ 100 cm³
• 100 cm³ = 0.100 dm³

Step 4: Calculate solubility in mol/dm³

\[ \text{Solubility} = \frac{\text{Moles of solute}}{\text{Volume of solvent in dm³}} = \frac{0.25}{0.100} = 2.50 \; \text{mol/dm³} \]

Correct Answer: 2.50