Look up the atomic masses of each element in sucrose:
• C has an atomic mass of 12.011 u
• H has an atomic mass of 1.008 u
• O has an atomic mass of 15.999 u
Sucrose consists of 12 C atoms, 22 H atoms, and 11 O atoms, so one molecule has an atomic mass of about
12 (12.011 u) + 22 (1.008 u) + 11 (15.999 u) ≈ 342.3 u
Then
• C makes up (12 (12.011 u)) / (342.3 u) ≈ 0.4211 = 42.11%,
• H makes up (22 (1.008 u)) / (342.3 u) ≈ 0.06479 = 6.479%, and
• O makes up (11 (15.999 u)) / (342.3 u) ≈ 0.5141 = 51.41%
of sucrose
