Question

"No precipitation reaction can occur without exchange of ions between the two reactants." Justify this statement giving a balanced chemical equation for the reaction.

Answer 1

1. The statement "No precipitation reaction can occur without exchange of ions between the two reactants" is based on the principle that precipitation reactions involve the formation of an insoluble salt through the combination of ions from different reactants.
2. In these reactions, cations and anions in the solution combine to form an insoluble solid called a precipitate.
3. Consider the precipitation reaction between silver nitrate \[\ce{(AgNO3)}\] and sodium chloride \[\ce{(NaCl)}\] to produce silver chloride \[\ce{(AgCl)}\] as a precipitate.\[\ce{AgNO3_{(aq)} + NaCl _{(aq)} -> AgCl_{(s)} + NaNO3_{(aq)}}\] In this reaction, ions are exchanged between the two reactants:
   1. In AgNO3, silver ions \[\ce{(Ag+)}\] and nitrate ions \[\ce{(NO^3-)}\] are present.
   2. In \[\ce{NaCl}\], sodium ions \[\ce{(Na+)}\] and chloride ions \[\ce{(Cl^−)}\] are present.
4. Upon mixing, the silver ions \[\ce{(Ag+)}\] from \[\ce{AgNO3}\] combine with the chloride ions \[\ce{(CI^−)}\] from \[\ce{NaCl}\] to form the insoluble silver chloride \[\ce{(AgCl)}\] precipitate.
5. The sodium and nitrate ions remain in the solution as they are soluble.
6. Precipitation processes rely heavily on the exchange of ions, and the development of a solid precipitate is a clear indicator of the reaction.