Question

Write balanced net ionic equations for the following reactions, and label the conjugate acid-base pairs: (a) \(\mathrm{HNO}_{3}(a q)+\mathrm{Li}_{2} \mathrm{CO}_{3}(a q) \rightleftharpoons \mathrm{LiNO}_{3}(a q)+\mathrm{LiHCO}_{3}(a q)\) (b) \(2 \mathrm{NH}_{4} \mathrm{Cl}(a q)+\mathrm{Ba}(\mathrm{OH})_{2}(a q) \rightleftharpoons 2 \mathrm{H}_{2} \mathrm{O}(I)+\mathrm{BaCl}_{2}(a q)+2 \mathrm{NH}_{3}(a q)\)

Short answer

The net ionic equations are \(\mathrm{H}^{+}(aq) + \mathrm{CO}_{3}^{2-}(aq) \rightleftharpoons \mathrm{HCO}_{3}^{-}(aq)\) and \(2\mathrm{NH}_{4}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightleftharpoons 2\mathrm{H}_{2} \mathrm{O}(l) + 2\mathrm{NH}_{3}(aq)\). The conjugate acid-base pairs are \(\mathrm{H}^{+}\)/\(\mathrm{HCO}_{3}^{-}\), \(\mathrm{CO}_{3}^{2-}\)/\(\mathrm{HCO}_{3}^{-}\), \(\mathrm{NH}_{4}^{+}\)/\(\mathrm{NH}_{3}\), and \(\mathrm{OH}^{-}\)/\(\mathrm{H}_{2} \mathrm{O}\).

Step-by-step solution

Identify the Reactants and Products

Begin by identifying all the reactants and products in each given reaction. For (a), the reactants are \(\mathrm{HNO}_{3}(aq)\) and \(\mathrm{Li}_{2}\mathrm{CO}_{3}(aq)\), and the products are \(\mathrm{LiNO}_{3}(aq)\) and \(\mathrm{LiHCO}_{3}(aq)\). For (b), the reactants are \(2\mathrm{NH}_{4} \mathrm{Cl}(aq)\) and \(\mathrm{Ba}(\mathrm{OH})_{2}(aq)\), and the products are \(2\ \mathrm{H}_{2} \mathrm{O}(l)\), \(\mathrm{BaCl}_{2}(aq)\), and \(2\ \mathrm{NH}_{3}(aq)\).

Write Complete Ionic Equations

Break each compound into its respective ions. For reaction (a), \(\mathrm{HNO}_{3}(aq) + \mathrm{Li}_{2}\mathrm{CO}_{3}(aq) \rightleftharpoons \mathrm{LiNO}_{3}(aq) + \mathrm{LiHCO}_{3}(aq)\): \[ \mathrm{H}^{+}(aq) + \mathrm{NO}_{3}^{-}(aq) + 2\mathrm{Li}^{+}(aq) + \mathrm{CO}_{3}^{2-}(aq) \rightleftharpoons 2\mathrm{Li}^{+}(aq) + \mathrm{NO}_{3}^{-}(aq) + \mathrm{Li}^{+}(aq) + \mathrm{HCO}_{3}^{-}(aq)\] For reaction (b), \(2\mathrm{NH}_{4} \mathrm{Cl}(aq) + \mathrm{Ba}(\mathrm{OH})_{2}(aq) \rightleftharpoons 2\mathrm{H}_{2} \mathrm{O}(l) + \mathrm{BaCl}_{2}(aq) + 2\mathrm{NH}_{3}(aq)\): \[2\mathrm{NH}_{4}^{+}(aq) + 2\mathrm{Cl}^{-}(aq) + \mathrm{Ba}^{2+}(aq) + 2\mathrm{OH}^{-}(aq) \rightleftharpoons 2\mathrm{H}_{2} \mathrm{O}(l) + \mathrm{Ba}^{2+}(aq) + 2\mathrm{Cl}^{-}(aq) + 2\mathrm{NH}_{3}(aq)\]

Cancel the Spectator Ions

Identify and cancel the spectator ions present on both sides of the equations.For reaction (a), cancel \(\mathrm{NO}_{3}^{-}\) and \(2\mathrm{Li}^{+}\). The net ionic equation becomes: \[\mathrm{H}^{+}(aq) + \mathrm{CO}_{3}^{2-}(aq) \rightleftharpoons \mathrm{HCO}_{3}^{-}(aq) \]

Write the Net Ionic Equation for (b)

In reaction (b), cancel \(\mathrm{Cl}^{-}\) and \(\mathrm{Ba}^{2+}\). The net ionic equation becomes: \[2\mathrm{NH}_{4}^{+}(aq) + 2\mathrm{OH}^{-}(aq) \rightleftharpoons 2\mathrm{H}_{2} \mathrm{O}(l) + 2\mathrm{NH}_{3}(aq)\]

Identify the Conjugate Acid-Base Pairs

In reaction (a), the conjugate acid-base pairs are \(\mathrm{H}^{+}\) (acid) and \(\mathrm{HCO}_{3}^{-}\) (conjugate base), and \(\mathrm{CO}_{3}^{2-}\) (base) and \(\mathrm{HCO}_{3}^{-}\) (conjugate acid). For reaction (b), the pairs are \(\mathrm{NH}_{4}^{+}\) (acid) and \(\mathrm{NH}_{3}\) (conjugate base), and \(\mathrm{OH}^{-}\) (base) and \(\mathrm{H}_{2} \mathrm{O}\) (conjugate acid).

Key concepts

Acid-Base Reactions

Understanding acid-base reactions is crucial for writing balanced ionic equations. In these reactions, acids donate protons (H⁺ ions) while bases accept protons. For example, in reaction (a), nitric acid (HNO₃) acts as an acid, and lithium carbonate (Li₂CO₃) acts as a base. During the reaction, the acid and base exchange ions to form new products. This exchange is key to predicting the outcome of many chemical reactions.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are fundamental to understanding the dynamics of acid-base reactions. When an acid donates a proton, it forms its conjugate base, and when a base accepts a proton, it forms its conjugate acid. For example, in reaction (a), H⁺ (the conjugate acid) and HCO₃⁻ (the conjugate base) are one pair, while CO₃²⁻ (the base) and HCO₃⁻ (the conjugate acid) are another. Identifying these pairs helps us understand how acids and bases transform during reactions.

Ionic Equations

Ionic equations break down compounds into their respective ions. This helps in clearly seeing which ions participate in reaction and which do not (spectator ions). For instance, in reaction (b), the complete ionic equation is:

2NH₄⁺(aq) + 2Cl⁻(aq) + Ba²⁺(aq) + 2OH⁻(aq) ⇌ 2H₂O(l) + Ba²⁺(aq) + 2Cl⁻(aq) + 2NH₃(aq)

By canceling the spectator ions (Cl⁻ and Ba²⁺), we get the net ionic equation:
2NH₄⁺(aq) + 2OH⁻(aq) ⇌ 2H₂O(l) + 2NH₃(aq).

This simplification helps in focusing on the actual chemical change occurring in the reaction.