Theory:

We have learnt the number of entities present in a given substance so far. However, the percentage of a specific element present in a compound is frequently required.
The percentage composition of a compound represents the mass of each element present in \(100\) \(g\) of the compound.
The formula for calculating the mass percent of an element is given below:
 
Masspercentofanelement=MassoftheelementinthecompoundMolecularmassofthecompound×100
  
Let us look at few examples for calculating percentage composition.
 
Example: \(1\)
 
Calculate the mass percent of water (\(H_2O\)).
 
Solution:
 
MolecularmassofH2O=21+16=18g
 
Masspercentofhydrogen=218×100=11.11%Masspercentofoxygen=1618×100=88.89%
 
Example: \(2\)
 
Calculate the mass percent of methane (\(CH_4\)).
 
Solution:
 
MolecularmassofCH4=12+4=16g
 
Masspercentofcarbon=1216×100=75%Masspercentofhydrogen=416×100=25%
 
This percentage composition is used for determining the empirical formula and molecular formula.