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 lose electrons to form ions. These ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking place by means of ions. However when done so, it is called total 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.
The ionic reactions are single or double displacement reactions and are possible only with electrolytes.
Br2(l) + 2 NaI(aq) -----------> 2 NaBr(aq) + I2(s)
Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionic 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 equation, write the ionic forms as
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 equation is written as
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s).
CaCl2(aq)--------------> Ca2+(aq) +2Cl−(aq)
2AgNO3(aq)-----------------> 2Ag+ (aq)+ 2NO3−(aq)
Thus the total ionic equation would be:
When reactions take place in aqueous medium that is, in presence of water, the atoms in the molecule either gain or lose electrons to form ions. These ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking place by means of ions. However when done so, it is called total ionic equation.
Introduction to 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.
The ionic reactions are single or double displacement reactions and are possible only with electrolytes.
Total ionic equation: Illustration-I
Let us consider a reaction of iodine precipitation from bromine and sodium iodide.Br2(l) + 2 NaI(aq) -----------> 2 NaBr(aq) + I2(s)
Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionic 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 equation, write the ionic forms as
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 equation is written as
Br2(l) + 2 Na+(aq) +2 I-(aq) -----> 2 Na+(aq) + 2 Br-(aq) + I2(s).
Total ionic equation: Illustration-II
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- Consider another example of formation of silver chloride from silver nitrate
CaCl2(aq) + 2AgNO3(aq)
Ca(NO3)2(aq) + 2AgCl(s)
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)
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