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: Finding Mass of Zinc in Zinc Sulphate Crystals **Given Information:** - Zinc sulphate crystals contain 22.65% Zn - Total crystal mass = 40 g - Need to find mass of Zn required **Step 1: 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. Therefore, the percentage composition remains constant regardless of the sample size. **Step 2: Calculate Mass of Zinc** If zinc sulphate crystals contain 22.65% Zn by mass, then: $$\text{Mass of Zn} = \frac{22.65}{100} \times 40 \text{ g}$$ $$\text{Mass of Zn} = 0.2265 \times 40$$ $$\text{Mass of Zn} = 9.06 \text{ g}$$ **Answer: 9.06 g (or approximately 9.1 g)** **Why This Works:** The 22.65% composition is invariant—whether analyzing 1 g or 40 g of the crystals, zinc always constitutes 22.65% of the total mass. This directly follows from the law of constant proportions, which guarantees fixed elemental ratios in any sample of a pure compound.