Carbonate decomposition mass loss depends on CO2 percentage by mass

Steps:

• Decomposition reaction: MCO3 → MO + CO2 (or Li2CO3 → Li2O + CO2), mass loss equals CO2 mass.
• For 5 g samples, loss is proportional to (molar mass CO2 / molar mass carbonate) × 5 g.
• Calculate molar masses: Li2CO3 (74 g/mol), MgCO3 (84 g/mol), CuCO3 (123.5 g/mol), BaCO3 (197 g/mol).
• CO2 percentage highest for lowest-molar-mass carbonate: Li2CO3 (44/74 ≈ 59.5%), so greatest loss (≈2.97 g).

Why C is correct:

• Lithium carbonate (Li2CO3) has the lowest molar mass, maximizing CO2 fraction per the decomposition formula, yielding highest mass loss from 5 g.

Why the others are wrong:

• A: Barium carbonate's high Ba atomic mass (137) minimizes CO2 percentage (≈22%).
• B: Copper(II) carbonate's Cu mass (63.5) reduces CO2 percentage (≈36%).
• D: Magnesium carbonate's Mg mass (24) gives moderate CO2 percentage (≈52%), less than lithium.

Final answer: C