Take C = 12, H = 1, O = 16. What is the percentage by mass of oxygen in ethanol, C₂H₅OH?
Correct answer B. 34.8%
Explanation
Molar mass of C₂H₅OH = 24 + 6 + 16 = 46 g/mol. Percentage of oxygen = (16/46) × 100 = 34.8%. The value 52.2% is the carbon percentage.
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