Zinc sulphate contains 22.65% Zn and 43.9% . If the law of constant proportions is true, then the ma — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question

💡 Solution & Explanation

# Solution: Mass of Zinc in Zinc Sulphate Crystals **Step 1: Identify the composition** Zinc sulphate crystals contain: - Zn: 22.65% - $H_2O$: 43.9% - Therefore, $SO_4$: 100% − 22.65% − 43.9% = 33.45% **Step 2: Apply the law of constant proportions** The law of constant proportions states that a compound always contains the same elements in the same mass ratio, regardless of source or amount. **Step 3: Calculate mass of Zn in 40g crystals** If the crystals contain 22.65% Zn by mass: $$\text{Mass of Zn} = 40 \text{ g} \times \frac{22.65}{100} = 9.06 \text{ g}$$ **Step 4: Verify the formula** This corresponds to $ZnSO_4 \cdot 7H_2O$ (heptahydrate), where: - Molar mass = 65 + 96 + 126 = 287 g/mol - Zn percentage = $\frac{65}{287} \times 100 = 22.65\%$ ✓ **Answer: 9.06 g of Zn** is required to produce 40g of zinc sulphate crystals, following the constant mass ratio guaranteed by the law of constant proportions.