Ions are formed when electrons are either added or removed from the
atoms. Chemical reactions are represented by simple molecular formulas. However the reactions actually take place by means of ions.
When reactions take place in aqueous medium that is, in presence of water, the atoms in the molecule either gain or loose electrons to form ions. these ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking by means of ions.However when done so,it is called total ionic equation.
Following denotions are used while writing the ionic equation.
(l) in the subscript means the compound is in its liquid state,
(s) in the subscript means solid state.
(g) in the subscript means gas state.
(aq) Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionically bonded compound,would dissociate into ions in water ,hence represented by (aq), Same about sodium bromide too. However the iodine molecule in the products is insoluble in water and hence shown as solid which precipitates.
To write the total ionic reaction,write the ionic forms,
2NaI ------------>2 Na+(aq) +2 I-(aq)
Br2--------------->2Br-(aq)
Also in the products,
2 NaBr(aq)---------------> 2 Na+(aq) + 2 Br-(aq)
Thus the total ionic reaction is written as
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s),
But since some ions i.e.Na+(aq) are present on both sides,they can be said to have not taken part in the reaction and hence treated as spectator ions. So if we overlook these ions from both sides,
The net ionic reaction is :-
Br2(l) + 2I-(aq) -----> 2Br-(aq) + I2(s)
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s)
CaCl2(aq) + 2AgNO3(aq) Ca(NO3)2(aq) + 2AgCl(s)
The dissociation would be
CaCl2(aq)--------------> Ca2+(aq) +2Cl−(aq)#
2AgNO3(aq)-----------------> 2Ag+ (aq)+ 2NO3−(aq)
Thus the total ionic equation would be:
Ca2+(aq) + 2Cl− (aq)+ 2Ag+(aq) + 2NO3−(aq) Ca2+(aq) + 2NO3− (aq)+ 2AgCl(s)
The net ionic reaction is
Ca2+(aq) + 2Cl− (aq)+ 2Ag+(aq) + 2NO3−(aq) ---------> Ca2+(aq) + 2NO3− (aq)+ 2AgCl(s)
2Cl− (aq)+ 2Ag+(aq)------------------> 2AgCl(s)
When reactions take place in aqueous medium that is, in presence of water, the atoms in the molecule either gain or loose electrons to form ions. these ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking by means of ions.However when done so,it is called total ionic equation.
Following denotions are used while writing the ionic equation.
(l) in the subscript means the compound is in its liquid state,
(s) in the subscript means solid state.
(g) in the subscript means gas state.
Illustration of writing net ionic equations
2NaI (aq) +Br2 (aq)--------------->2NaBr (aq) +I2(s)(aq) Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionically bonded compound,would dissociate into ions in water ,hence represented by (aq), Same about sodium bromide too. However the iodine molecule in the products is insoluble in water and hence shown as solid which precipitates.
To write the total ionic reaction,write the ionic forms,
2NaI ------------>2 Na+(aq) +2 I-(aq)
Br2--------------->2Br-(aq)
Also in the products,
2 NaBr(aq)---------------> 2 Na+(aq) + 2 Br-(aq)
Thus the total ionic reaction is written as
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s),
But since some ions i.e.Na+(aq) are present on both sides,they can be said to have not taken part in the reaction and hence treated as spectator ions. So if we overlook these ions from both sides,
The net ionic reaction is :-
Br2(l) + 2I-(aq) -----> 2Br-(aq) + I2(s)
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s)
Illustration II of writing net ionic equations
Consider another example of formation of silver chloride from silver nitrateCaCl2(aq) + 2AgNO3(aq) Ca(NO3)2(aq) + 2AgCl(s)
The dissociation would be
CaCl2(aq)--------------> Ca2+(aq) +2Cl−(aq)#
2AgNO3(aq)-----------------> 2Ag+ (aq)+ 2NO3−(aq)
Thus the total ionic equation would be:
Ca2+(aq) + 2Cl− (aq)+ 2Ag+(aq) + 2NO3−(aq) Ca2+(aq) + 2NO3− (aq)+ 2AgCl(s)
The net ionic reaction is
Ca2+(aq) + 2Cl− (aq)+ 2Ag+(aq) + 2NO3−(aq) ---------> Ca2+(aq) + 2NO3− (aq)+ 2AgCl(s)
2Cl− (aq)+ 2Ag+(aq)------------------> 2AgCl(s)
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