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?
Chemical Formula
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
Formula of Compounds
For Ex:Water(H2O),carbon dioxide(CO2),sulphur dioxide(SO2),ammonia(NH3), methane(CH4),ethanol(CH3CH2OH) etc.
For Ex:Water(H2O),carbon dioxide(CO2),sulphur dioxide(SO2),ammonia(NH3), methane(CH4),ethanol(CH3CH2OH) etc.
Molecular Mass
The molecular mass of a substance is relative mass of its molecules as compared with mass of C-12 atom taken as 12 units.
or
The molecular mass is equal to sum of its atomic masses of all the atoms present in one molecule of substance.
The molecular mass of a substance is relative mass of its molecules as compared with mass of C-12 atom taken as 12 units.
or
The molecular mass is equal to sum of its atomic masses of all the atoms present in one molecule of substance.
For Ex:Water(H2O)
Atomic mass of H= 1 u
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
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
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