Ionic Equations
An
ionic equation shows only
the ions
that participate in a chemical
reaction producing a new substance
that has a change in state; for example, a product that precipitates
from two aqueous solution reactants.
Example 1
The reaction between soluble lead nitrate, Pb(NO3)2 and soluble potassium iodide, KI, produces insoluble lead iodide, PbI2, which precipitates, and soluble potassium nitrate KNO3 (which remains as dissociated ions in the solution).
The chemical equation is written as
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
The ionic equation for the above is
Pb2+(aq) + 2I-(aq) → PbI2(s)
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
In the ionic equation, the dissociated aqueous lead Pb2+ ion of the lead nitrate reactant is chosen because it changes to a precipitate.
The same goes for the dissociated aqueous iodide I-(aq) ion.
Example 2
The reaction between hydrochloric acid and sodium carbonate produces the salt sodium chloride, carbon dioxide and water.
The chemical equation is written as
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
The ionic equation is written as
2H+(aq) + CO32-(aq) → CO2(g) + H2O(l)
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
Example 3
The neutralisation reaction between hydrochloric acid and sodium hydroxide produces the salt sodium chloride and water.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The ionic equation for the neutralisation reaction can be written as
H+(aq) + OH-(aq) → H2O(l)
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Example 1
The reaction between soluble lead nitrate, Pb(NO3)2 and soluble potassium iodide, KI, produces insoluble lead iodide, PbI2, which precipitates, and soluble potassium nitrate KNO3 (which remains as dissociated ions in the solution).
The chemical equation is written as
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
The ionic equation for the above is
Pb2+(aq) + 2I-(aq) → PbI2(s)
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
In the ionic equation, the dissociated aqueous lead Pb2+ ion of the lead nitrate reactant is chosen because it changes to a precipitate.
The same goes for the dissociated aqueous iodide I-(aq) ion.
Example 2
The reaction between hydrochloric acid and sodium carbonate produces the salt sodium chloride, carbon dioxide and water.
The chemical equation is written as
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
The ionic equation is written as
2H+(aq) + CO32-(aq) → CO2(g) + H2O(l)
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
Example 3
The neutralisation reaction between hydrochloric acid and sodium hydroxide produces the salt sodium chloride and water.
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The ionic equation for the neutralisation reaction can be written as
H+(aq) + OH-(aq) → H2O(l)
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
