A sample of has Ca = 40%, C = 12% and O = 48%. If the law of constant proportions is true, then the — Mole Concept and Some Basic Concepts of Chemistry Chemistry Question

💡 Solution & Explanation

# Solution: Law of Constant Proportions **Understanding the Law:** The law of constant proportions states that a compound always contains the same elements in the same mass ratio, regardless of its source. **Step 1: Identify the given composition** - Ca = 40% - C = 12% - O = 48% These percentages represent the constant mass ratio in any pure sample of $CaCO_3$. **Step 2: Apply to the 5 g sample** If 5 g of $CaCO_3$ from another source obeys the law of constant proportions, it must have the same composition: $$\text{Mass of Ca} = 5 \text{ g} \times \frac{40}{100} = 2 \text{ g}$$ **Step 3: Verify with molar mass** - Molar mass of $CaCO_3$ = 40 + 12 + 48 = 100 g/mol - Mass fraction of Ca = $\frac{40}{100} = 0.40$ ✓ This confirms the 40% composition is consistent. **Conclusion:** By the law of constant proportions, **2 g of Ca** will be present in any 5 g sample of pure $CaCO_3$, regardless of its source. The mass ratio of elements in a compound is invariant.