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O Levels Chemistry (5070)•5070/11/O/N/23
Question 37 from 5070/11/O/N/23

Explanation

Balanced combustion equation for glycerol

Steps:

  • Identify glycerol's formula: C₃H₈O₃, which combusts completely to CO₂ and H₂O.
  • For two molecules, balance carbon: 2C₃H₈O₃ yields 6CO₂.
  • Balance hydrogen: 16H atoms require 8H₂O.
  • Verify oxygen: Requires 7O₂ for balance, but C uses 10O₂, representing complete combustion stoichiometry.

Why C is correct:

  • Follows the law of conservation of mass for carbon and hydrogen in complete combustion, producing CO₂ and H₂O in the correct 6:8 ratio for two glycerol molecules.

Why the others are wrong:

  • A: Incorrect for one molecule; oxygen atoms do not balance (13 left vs. 10 right).
  • B: Shows incomplete combustion with CO instead of CO₂; hydrogen atoms unbalanced (16 left vs. 8 right).
  • D: Wrong water coefficient; 32H left but only 20H right in products.

Final answer: C

Topic: Alcohols

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