Example 4.2: Molecular and Ionic Equations
When carbon dioxide is dissolved in an aqueous solution of sodium hydroxide, the mixture reacts to yield aqueous sodium carbonate and liquid water. Write balanced molecular, complete ionic, and net ionic equations for this process.
Solution
Begin by identifying formulas for the reactants and products and arranging them properly in chemical equation form:
\(\ce{CO2(aq)}\)\(\ce{ + }\)\(\ce{NaOH(aq)}\)\(\ce{->}\)\(\ce{Na2CO3(aq)}\)\(\ce{ + }\)\(\ce{H2O(l)}\)\(\ce{ }\) (unbalanced)
Balance is achieved easily in this case by changing the coefficient for
\(\ce{NaOH}\) to
2, resulting in the molecular equation for this reaction:
\(\ce{CO2(aq)}\)\(\ce{ + }\)\(\ce{2NaOH(aq)}\)\(\ce{->}\)\(\ce{Na2CO3(aq)}\)\(\ce{ + }\)\(\ce{H2O(l)}\)\(\ce{ }\) balanced
The two dissolved ionic compounds,
\(\ce{NaOH}\) and
\(\ce{Na2CO3}\), can be represented as dissociated ions to yield the complete ionic equation:
\(\ce{CO2(aq)}\)\(\ce{ + }\)\(\ce{2Na+ (aq)}\)\(\ce{ + }\)\(\ce{2OH- (aq)}\)\(\ce{->}\)\(\ce{2Na+ (aq)}\)\(\ce{ + }\)\(\ce{CO3^2- (aq)}\)\(\ce{ + }\)\(\ce{H2O(l)}\)\(\ce{ }\) Complete ionic
Finally, identify the spectator ion(s), in this case
\(\ce{Na+(aq)}\), and remove it from each side of the equation to generate the net ionic equation:
\(\ce{CO2(aq)}\)\(\ce{ + }\)\(\ce{2OH-(aq)}\)\(\ce{->}\)\(\ce{CO3^2-(aq)}\)\(\ce{ + }\)\(\ce{H2O(l)}\)\(\ce{ }\) Net ionic