Question

Write the net ionic equation for the reaction of \(\mathrm{BaCl}_{2}(\mathrm{aq})\) and \(\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})\). You may have to consult the solubility rules.

Short answer

The net ionic equation is \[ \mathrm{Ba}^{2+}(\mathrm{aq}) + \mathrm{SO}_4^{2-}(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{s}) \].

Step-by-step solution

Write the balanced molecular equation

First, we write the balanced molecular equation for the reaction between barium chloride \(\mathrm{BaCl}_2\) and sodium sulfate \(\mathrm{Na}_2\mathrm{SO}_4\). This forms barium sulfate \(\mathrm{BaSO}_4\) and sodium chloride \(\mathrm{NaCl}\). The balanced equation is: \[ \mathrm{BaCl}_2(\mathrm{aq}) + \mathrm{Na}_2\mathrm{SO}_4(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{s}) + 2\,\mathrm{NaCl}(\mathrm{aq}) \]

Identify the spectator ions

In this reaction, the spectator ions are those that do not participate in forming the precipitate. Sodium \(\mathrm{Na}^+\) and chloride \(\mathrm{Cl}^-\) ions remain in solution and do not form the precipitate. They appear unchanged on both sides of the molecular equation.

Write the complete ionic equation

Write all the compounds that are soluble in water as their ions. The complete ionic equation is: \[ \mathrm{Ba}^{2+}(\mathrm{aq}) + 2\,\mathrm{Cl}^-(\mathrm{aq}) + 2\,\mathrm{Na}^+(\mathrm{aq}) + \mathrm{SO}_4^{2-}(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{s}) + 2\,\mathrm{Na}^+(\mathrm{aq}) + 2\,\mathrm{Cl}^-(\mathrm{aq}) \]

Write the net ionic equation

To find the net ionic equation, we remove the spectator ions from the complete ionic equation. The net ionic equation focuses only on the ions that form the precipitate, barium sulfate: \[ \mathrm{Ba}^{2+}(\mathrm{aq}) + \mathrm{SO}_4^{2-}(\mathrm{aq}) \rightarrow \mathrm{BaSO}_4(\mathrm{s}) \]

Key concepts

Precipitation Reaction

A precipitation reaction occurs when two solutions containing soluble salts are combined, resulting in the formation of an insoluble solid, known as a precipitate. This type of reaction plays an essential role in various chemical processes by showing how ions combine to form new compounds.
In the example provided with barium chloride \( \mathrm{BaCl}_2 \) and sodium sulfate \( \mathrm{Na}_2\mathrm{SO}_4 \), when these solutions are mixed together, an insoluble compound, barium sulfate \( \mathrm{BaSO}_4 \), is formed. This solid precipitate can be observed as it separates from the solution.
The formation of a precipitate indicates a chemical change and involves the exchange of ions between the reactants, resulting in a solid product that is not soluble in water. Precipitation reactions are commonly used in labs to purify compounds and remove contaminants.

Solubility Rules

To predict whether a precipitate forms in a reaction, solubility rules are used. These rules help to determine which compounds dissolve in water and which do not. Understanding these rules is pivotal when writing net ionic equations.
For example:

• Most sulfate salts are soluble except for those of barium, lead, and calcium.
• Sodium (\( \mathrm{Na}^+ \)) and chloride (\( \mathrm{Cl}^- \)) ions typically form soluble compounds in water.

In the reaction of \( \mathrm{BaCl}_2 \) and \( \mathrm{Na}_2\mathrm{SO}_4 \), using solubility rules, we discover that \( \mathrm{BaSO}_4 \) is insoluble, and thus, it precipitates out of the solution. These rules help identify which ions will remain "active" during the reaction, allowing for the simplification of the ionic equation into its net form.

Spectator Ions

Spectator ions are ions present in the reaction mixture that do not participate in the actual chemical change. In the equations representing chemical reactions, they appear unchanged on both the reactant and product side.
Understanding spectator ions is crucial when writing net ionic equations, as they can be eliminated to focus on the ions that participate directly in forming the precipitate. This simplification helps to emphasize the chemical transformation occurring.
In the case of the reaction between \( \mathrm{BaCl}_2 \) and \( \mathrm{Na}_2\mathrm{SO}_4 \), the sodium \( \mathrm{Na}^+ \) and chloride \( \mathrm{Cl}^- \) ions are spectator ions. Since they do not change and remain in the dissolved aqueous form throughout the reaction, they can be excluded from the net ionic equation. Identifying these helps students to understand and correctly write net ionic equations by focusing on the active components.