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
Question
A sample of $CaCO_3$ has Ca = 40%, C = 12% and O = 48%. If the law of constant proportions is true, then the mass of Ca in 5 g of $CaCO_3$ from another source will be :
💡 Solution & Explanation
# Solution The law of constant proportions (law of definite proportions) states that a chemical compound always contains the same elements in the same fixed mass ratio, regardless of its source. **Step 1: Identify the composition from the given sample** The sample contains: - Ca = 40% - C = 12% - O = 48% These percentages represent the fixed mass ratio in any pure sample of $CaCO_3$. **Step 2: Apply the law to find mass of Ca in 5 g** Since the mass percentage of Ca is constant at 40% in all samples of $CaCO_3$: $$\text{Mass of Ca in 5 g} = \frac{40}{100} \times 5 \text{ g} = 2 \text{ g}$$ **Step 3: Verification** This can be verified by calculating the molar mass: - $CaCO_3$: Ca(40) + C(12) + O₃(48) = 100 g/mol - Mass fraction of Ca: $\frac{40}{100} = 40\%$ ✓ **Answer: 2 g of Ca will be present in 5 g of $CaCO_3$ from any source.** The law of constant proportions guarantees that the elemental composition by mass remains invariant across different samples of the same compound.