Chapter : 3. Atoms & Molecules
Mass percentage of an element from molecular formula
Mass percentage of an element from molecular formula : The molecular formula of a compound may be defined as the formula which specifies the number of atoms of various elements in the molecule of the compound.
Example. The molecular formula of glucose is C
6H
12O
6. This indicates that a molecule of glucose contains six atoms of carbon, twelve atoms of hydrogen and six atoms of oxygen.
The mass percentage of each element is then calculated by the following formula:
Example. Calculate the percentage composition (by mass) of formaldehyde (CH
2O).
Solution. Molecular mass of formaldehyde,
CH
2O = 12 × 1 + 1 × 2 + 16 × 1 = 30
Mass of one mole of formaldehyde = 30 g
1 Mole of CH
2O contains 1 mole (12 g) of carbon. 2 moles of hydrogen (2 g) and 1 mole of oxygen (16 g)
Percentage of carbon =
Percentage of hydrogen =
Percentage of oxygen =
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