CHM 1032C Learning Tools

  Total Ionic and Net Ionic Equations

 The presence (or lack) of a driving force for reactions done in water can be evaluated using a net ionic equation. The total and net ionic equations show the real physical state of every component of the reaction. The compound is a strong electrolyte (a soluble ionic compound or a strong acid), then the compound is separated into the appropriate aqueous ions. Otherwise it is left in an undisassociated (ionic compounds) state or un-ionized state (weak acids, bases and water). Example 1: CaCO3(s) + HCl ® ?

Molecular Equation: CaCO3(s) + 2HCl(aq) ® CaCl2(aq) + H2O(l) + CO2(g)

Total Ionic Equation: CaCO3(s) + 2H+(aq) + 2Cl-(aq) ® Ca2+(aq) + 2Cl-(aq) + H2O(l) + CO2(g)

Net Ionic Equation: CaCO3(s) + 2H+(aq) ® Ca2+(aq) + H2O(l) + CO2(g)

The driving force was the formation of water and gas!

Example 2: Fe(s) + AgNO3(aq) ® ?

Molecular Equation: Fe(s) + 2AgNO3(aq) ® 2Ag(s) + Fe(NO3)2(aq)

Total Ionic Equation: Fe(s) + 2Ag+(aq) + 2NO3-(aq) ® 2Ag(s) + Fe2+(aq) + 2NO3-(aq)

 Net Ionic Equation: Fe(s) + 2Ag+(aq) ® 2Ag(s) + Fe2+(aq)

The driving force was the transfer of electrons from iron (the reducing agent) to the silver ion (the oxidizing agent). Remember: The reducing agent is the reactant that donates the electrons to the reactant that is reduced. When the reducing agent loses electrons, it is oxidized. The oxidizing agent in the reactant that receives the electrons from the reactant that is oxidized. In doing so, the oxidizer is reduced.

Example 3: K3PO4(aq) + 3HNO3(aq) ® ?

Molecular Equation: K3PO4(aq) + 3HNO3(aq) ® H3PO4(aq) + 3KNO3(aq)

Total Ionic Equation:

3K+(aq) + PO43-(aq) + 3H+(aq) + 3NO3-(aq) ® H3PO4(aq) + 3K+(aq) + 3NO3-(aq)

Net Ionic Equation: PO43-(aq) + 3H+(aq) ® H3PO4(aq)

The driving force was the formation of the weakly ionized acid.

Example 4: KNO3(aq) + HCl(aq) ® ?

Molecular Equation: KNO3(aq) + HCl(aq) ® KCl(aq) + HNO3(aq)

Total Ionic Equation:

K+(aq) + NO3-(aq) + H+(aq)+ Cl-(aq) ® K+(aq) + Cl-(aq) + H+(aq) + NO3-(aq)

Net Ionic Equation: There is no net because all species remained as aqueous ions before and after my hypothesized double replacement reaction. The lack of a driving force leads me t0o conclude that the correct hypothesis is No Reaction.

 
Last modified December 28, 1998                Top        For more information, contact:  ksanchez@fccj.org