Empirical formula is the simplest (smallest) ratio of the each type of atom in a formula.
eg: In a compound having a formula of C6H12O6 find the empirical formula
elements C : H : O
Original ratio in the compound 6 : 12 : 6
Simplest ratio 1 : 2 :1
Empirical formula = CH2O
It is possible to calculate the empirical formula by obtaining the percentage by mass of a compound
e.g. A sample of the compound was analysed and found to contain 0.72 g of
carbon, 0.18 g of hydrogen and 0.96 g of oxygen. Find the empirical formula of the compound
1. Write the elements present in the compound
C H O
2. Write the percentages of masses in each element
0.72 0.18 0.96
3. Find the mole ratio of each atom by dividing the percentage mass by the relative atomic mass
0.72/12 0.18/1 0.96/16
=0.06 =0.18 = 0.06
4. Divide by the smallest number to get a whole number ratio (if this step does not produce whole numbers try more divisions, multiplications and rounding up)
0.06/0.06 0.18/0.06 0.06/0.06
=1 =3 =1
5. Now you can write the empirical formula by using the above ratios
CH3O