Question 1 What is a chemical formula?
Question 2 Give few examples of formulae of elements?
Question 3 Give few examples of formulae of compounds?
Question 4 Define molecular mass?
A chemical formula represents the composition of a molecule of the substance in terms of the symbols of elements present in the molecule.
Formulae of Elements
For Ex:Hydrogen(H2),Nitrogen(N2),Oxygen(O2),Chlorine(Cl2),Bromine(Br2) etc
For Ex:Water(H2O),carbon dioxide(CO2),sulphur dioxide(SO2),ammonia(NH3), methane(CH4),ethanol(CH3CH2OH) etc.
The molecular mass of a substance is relative mass of its molecules as compared with mass of C-12 atom taken as 12 units.
The molecular mass is equal to sum of its atomic masses of all the atoms present in one molecule of substance.
Atomic mass of O =16 u
Molecular mass of water =2 × atomic mass of H+1 × atomic mass of O
=2 × 1 + 16 × 1
= 18 u