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O Levels Chemistry (5070)•5070/12/O/N/24
Question 10 from 5070/12/O/N/24

Explanation

Empirical formula from mass percentages Steps:

  • Calculate oxygen mass percent: 100% - 48.6% - 8.1% = 43.3%.
  • Convert to moles assuming 100 g sample: C = 48.6/12 = 4.05 mol, H = 8.1/1 = 8.1 mol, O = 43.3/16 = 2.706 mol.
  • Divide each by smallest moles (2.706): C = 1.5, H = 3.0, O = 1.0.
  • Multiply by 2 for whole numbers: C₃H₆O₂.

Why none match:

  • Calculated formula C₃H₆O₂ (48.6% C, 8.1% H, 43.3% O) fits data exactly per mole ratio definition.

Why the others are wrong:

  • A and C (CH₂O): Yields 40% C, 6.7% H; C percentage too low.
  • B (C₂H₃O₂): Yields 40.7% C, 5.1% H; both C and H percentages mismatch.
  • D (C₂H₅O₂): Yields 39.3% C, 8.2% H; C percentage too low.

Final answer: C₃H₆O₂

Topic: Formulae

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