Question

calculate the percentage of composition for all the elements in glucose, C6H12O6?

Answer 1

Start by finding the atomic weights from your text book.
Carbon = 12.01 g/mol
Hydrogen = 1.01 g/mol
Oxygen = 16.00 g/mol

Work out the molecular weight of glucose:
Molecular weight of glucose = (6 x 12.01) + (12 x 1.01) + (6 x 16.00)
Molecular weight of glucose = 72.06 + 12.12 + 96.00
Molecular weight of glucose = 180.18 g/mol

The percentages are then derived from the weight of the individual elements:

Carbon = (72.06 / 180.18) x 100 = 40.0%
Hydrogen = (12.12 / 180.18) x 100 = 6.7%
Oxygen = (96.00 / 180.18) x 100 = 53.3%