Molecular and Ionic equations.
(1) Molecular equations: When the reactants and products involved in a chemical change are
written in molecular forms in the chemical equation, it is termed as molecular equation.
Examples: (i)
2222
24 ClOHMnClHClMnO
(ii)
4223
22 SnClFeClSnClFeCl
In above examples, the reactants and products have been written in molecular forms, thus the
equation is termed as molecular equation.
(2) Ionic equations:When the reactants and products involved in a chemical change are ionic
compounds, these will be present in the form of ions in the solution. The chemical change is
written in ionic forms in chemical equation, it is termed as ionic equation.
Examples: (i)
ClHMnO 44
2
22
2
22 ClOHClMn
(ii)
ClSnClFeClSnClFe 442262
4223
In above examples, the reactants and products have been written in ionic forms, thus the
equation is termed as ionic equation.
(3) Spectator ions:In ionic equations, the ions which do not undergo any change and equal in
number in both reactants and products are termed spectator ions and are not included in the
final balanced equations.
Example:
ClHZn 22
ClHZn 2
2
2
(Ionic equation)
H
Zn
2
2
2
HZn
(Final ionic equation)
In above example, the
Cl
ions are the spectator ions and hence are not included in the final
ionic balanced equation.
(4) Rules for writing ionic equations
(i) All soluble ionic compounds involved in a chemical change are expressed in ionic symbols
and covalent substances are written in molecular form. H
2
O, NH
3,
NO
2
, NO, SO
2
, CO, CO
2
, etc., are
expressed in molecular form.
(ii) The ionic compound which is highly insoluble is expressed in molecular form.
(iii) The ions which are common and equal in number on both sides, i.e., spectator
ions, are cancelled.
(iv) Besides the atoms, the ionic charges must also be balanced on both the sides.
The rules can be explained by following examples,
Example: Write the ionic equation for the reaction of sodium bicarbonate with sulphuric acid,
the molecular equation for the chemical change is,
NaHCO
3
+ H
2
SO
4
Na
2
SO
4
+ H
2
O + CO
2
NaHCO
3
, H
2
SO
4
and Na
2
SO
4
are ionic compounds, so these are written in ionic forms.
2
43
2 SOHHCONa
22
2
4
2 COOHSONa
Na
and
2
4
SO ions are spectator ions; hence these shall not appear in the final
equation.
HHCO 2
3
22
COOH
To make equal charges on both sides,
3
HCO should have a coefficient 2.
HHCO 22
3
22
COOH
In order to balance the hydrogen and carbon on both sides, the molecules of H
2
O and
CO
2
should have a coefficient 2 respectively.
HHCO 22
3 22
22 COOH or
HHCO
3 22
COOH
This is the balanced ionic equation.
Conversion of ionic equation in molecular form can be explained by following
example,
Example: Write the following ionic equation in the molecular form if the reactants are
chlorides.
2Fe
3+
+Sn
2+
2Fe
2+
+Sn
4+
For writing the reactants in molecular forms, the requisite number of chloride ions are
added.
ClSnClFe 262
23
or 2FeCl
3
+ SnCl
2
Similarly 8
Cl
ions are added on R.H.S. to neutralize the charges.
ClSnClFe 442
42
or 2FeCl
2
+ SnCl
4
Thus, the balanced molecular equation is, 2FeCl3+SnCl
2
= 2FeCl
2
+ SnCl
4
