The molecular equation for the
reaction between solutions of NaCl and Pb(NO3)2 is
–2NaCl(aq) + Pb(NO3)2 (aq) ® PbCl2 (s) + 2NaNO3 (aq)
When the soluble salts are represented
in the aqueous ionic form you get the full ionic equation
–2Na+ (aq) + 2Cl-(aq) + Pb2+ (aq) + 2 NO3 -(aq) ® PbCl2 (s) + 2Na+ (aq) + 2 NO3 -(aq)
Notice hydrated sodium and nitrate ions do not undergo any
change (and are referred to as spectator
ions); they remain in solution (in aqueous ionic form)
from start to finish, and as such can be eliminated from the equation giving
us
–2Cl-(aq)
+ Pb2+ (aq) ® PbCl2 (s)
The above equation showing only the
species that undergo change, showing only
the species that are involved in the reaction, is referred to as a (net) ionic equation.