How to find the empirical formula and molecular formula

Empirical formula is the simplest whole number ratio of various elements in the compound. Molecular formula is the actual number of atoms present in the compound. Here, we will discuss more about the E.F. and molecular formula of the compound.

What is empirical formula

E.F. is the simple whole number ratio of elements in the compound. There are few steps to calculate the E.F. of the compound.

  1. Divide the percentage of elements by respective atomic masses to form the moles.
  2. Calculate the simplest molar ratio by dividing each number of moles by the smallest number of moles
  3. Convert in to simple whole number ratio by multiplying with appropriate integers.
  4. This simple whole number ratio represents E.F.

Let’s solve the numerical below having C % = 24.27 H% = 4.07 Cl % = 71.65 Calculate the E.F. and M.F.

Following the steps above we will find the E.F. and M.F.

Empirical formula of compound = CH2Cl

n = M.mass / E.F. mass = 98.96 / 49.5 = 2

Molecular formula = n X E.F. = 2 X CH2Cl = C2H4Cl2

Empirical formula and Molecular formula calculation

What is molecular formula

Molecular formula is the actual number of atoms present in the compound.

Molecular formula = n X Empirical formula ( n = 1,2,3 )

n = Molecular mass / Empirical formula mass

Calculation of %age composition from formula

%age of any element = Mass of the element / Molecular mass of the compound X 100

FAQ’s on empirical formula and Molecular formula

  1. Are empirical formulas unique ?

Answer : E.F. is not unique. It can describe different chemical structures or isomers. But molecular formula is specific.

2. What is C6H12O6 called ?

Answer : Glucose is a sugar with a molecular formula C6H12O6

3. What is O2 called?

Answer : O2 is the molecular formula of the oxygen gas.

4. What is the relationship between M.M. and E.F.M.

Answer : M.M. = n X E.F.M.

Check out the structure of NH3 here

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