Chemistry


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 C6H12O6. 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 (CH2O).
Solution. Molecular mass of formaldehyde,
CH2O = 12 × 1 + 1 × 2 + 16 × 1 = 30
Mass of one mole of formaldehyde = 30 g
1 Mole of CH2O 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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