What is Chemical Formula?

The symbolic representation of a compound that shows elements in the compound and also the ratio of their atoms is called chemical formula.

As elements are represented by symbols .

Similarly, compounds are symbolically represented by chemical formulas .

CHEMICAL FORMULAS :

Calcium Carbonate = CaCO₃

Water = H₂O

Sulphuric acid = H₂SO₄

Benzene = C₆H₆

Types of Chemical Formulas:

There are different types of chemical formulas of a compound .i.e.. empirical formula, molecular formula ,structural formula etc.

Empirical Formula:

   The chemical formula that gives the simplest or the most reduced whole number ratio of atoms present in a compound is called empirical formula.

Benzene = CH

(Empirical Formula)

Molecular Formula:

   The chemical formula that gives the actual number of atoms present in one molecule of a compound is called molecular formula.

e.g.

Molecular formula of Benzene is C₆H₆

Molecular formula of Glucose is C₆H₁₂O₆

Why some compounds have same empirical and molecular formula ?

If the compound’s chemical formula can not be reduced any more then  their empirical formula is the same as  molecular formula .

Important questions for Exams !!!

Question 1:

Vinegar is 5% acetic acid . This contains 2 carbon atoms ,  four hydrogen atoms and 2 oxygen atoms. Write its empirical and molecular formulas ?

Given:

Number of carbon atoms = 2

Number of hydrogen atoms = 4

Number of oxygen atoms = 2

Find out its empirical and molecular formulas

Solution:

 Molecular formula      = C₂H₄O2          

Finding Empirical formula  as follow:

 Empirical formula   =   CH₂O 

Question 2:

Caffeine ( C₈H₁₀ N₄ O₂) is found in tea and coffee . Write its empirical formula ?

Given:

molecular formula      = C₈H₁₀ N4O2 

Find out its empirical formula

Solution:

Empirical formula   =   C₄H₅ N₂O

Difference b/w Empirical & Molecular Formula:

Empirical Formula	Molecular Formula
Simplest or most reduced whole number ratio of atoms present in a compound	Actual number of atoms present in a molecule of a compound
Determined directly by different methods e.g. Combustion analysis , Elemental analysis.	Can never determined directly, only determined as follow: Molecular formula = n x (Empirical formula)
Empirical formula is used for all compounds	Molecular formula is used for only molecular compounds
e.g. Glucose = CH2O Water = H2O	e.g. Glucose = C6H12O6 Water = H2O

Significance or Importance of a chemical formula:

i)It is a shorthand Expression

ii) It shows different kinds of elements present in a compound

iii) It shows the ratio of atoms present in a compound

iv) It represents one molecule or one Formula unit of a compound

v) It represents one mole of a compound

vi) It shows the number of atoms present in one molecule

vii) It shows the number of Ions present in one Formula unit

vii) It shows the number of moles of each element in one mole of a compound

For e.g one molecule of Sulphuric acid (H₂SO₄) contains 2-atoms of H, 1-atom of Sulphur, and 4 – atoms of oxygen. One mole of H₂SO=4contains= 2 moles of H, 1-mole of S, and 4-moleOxygen-atoms.

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