Test: Empirical Formula & Mass Calculations - NEET MCQ

Empirical formula of mass CH = (12 + 1) = 13 
Molecular formula = Empirical formula x n

Empirical Formula:

The empirical formula of a substance represents the simplest relative whole number ratio of the atoms of each element contained in the molecule of the substance.

Example: the empirical formula for glucose is CH₂O. Thus the molecule of glucose contains atoms of carbon, hydrogen and oxygen in the ratio 1:2:1.

Empirical formula represents the simplest whole number ratio of various atoms in a compound hence here n=2 and the empirical formula is C₂H₄O.

Molecular mass of the gas = Molecular mass of N₂ = 28 g 

Molecular formula mass = n X (Empirical formula mass) 

Empirical formula mass of the gas = 12 + 2 = 14 g 

Therefore, n = 28/14 = 2 

Hence the molecular formula is (CH₂)₂ or C₂H₄. 

The empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound.

Molecular formula of glucose is C₆H₁₂O₆.

Its empirical formula is CH₂O.

For CH₃COOH, the empirical formula is also CH₂O.

The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound

Both molecular mass and formula mass signify the same thing.

Formula unit mass is the term used for mass of ionic compounds.  Similarly, molecular mass is used for mass of covalent compounds (molecules).

The only reason we use two different terms is because molecules are covalent compounds meaning they have only non-metals. So ionic compounds cannot be a molecule and therefore it would not make sense to find the molecular mass for an ionic compound, so we just call it the "formula mass", when we are talking about ionic compounds.

Molecular mass: For covalent compounds, compounds that contain only non-metals such as SO₂, CO₂ etc.

Formula mass: For ionic compound, compounds that contain metals and non-metals such as Na₂CO₃, K₂CO₃ etc.

Empirical formula represents the simplest whole number ratio of various atoms in a compound hence for both C₂H₂ and C₂H₆ the empirical formula is CH.

Empirical formula mass is (2 X 12) + 1 + 80 = 105g and molar mass of the compound is 314 g/mol.

Hence, n = 3

Therefore, the molecular formula is C₆H₃Br₃.

Empirical formula of an acid is CH₂O₂

(Empirical formula) ×n= molecular formular

n = Whole number multiple i.e 1,2,3,4......

if n=1 molecular formula CH₂O₂

Empirical formula mass = 49.5 g.

Molecular mass = 99 g

Therefore n = 2

Therefore molecular formula of compound = (CH₂Cl)₂

Molecular formula of the compound is (C₅H₄)_n
since here n = 2 therefore molecular formula will be C₁₀H₈.