Question

Write formula equations and net ionic equations for the hydrolysis of each salt in water. a. sodium carbonate b. ammonium bromide

Short answer

a. Sodium Carbonate Formula Equation: \( CO3^{2-} + H2O \rightarrow HCO3^- + OH^- \) Net Ionic Equation: \( CO3^{2-} + H2O \rightarrow HCO3^- + OH^- \) b. Ammonium Bromide Formula Equation: \( NH4^+ + H2O \rightarrow NH3 + H3O^+ \) Net Ionic Equation: \( NH4^+ + H2O \rightarrow NH3 + H3O^+ \)

Step-by-step solution

a. Sodium Carbonate

Step 1: Identify the ions Sodium carbonate (Na2CO3) dissociates into sodium ions (Na+) and carbonate ions (CO3^2-) when dissolved in water. Step 2: Write the formula equation Reaction of carbonate ions with water: \( CO3^{2-} + H2O \rightarrow HCO3^- + OH^- \) Step 3: Write the net ionic equation Since the sodium ions do not participate in the reaction, they are considered as spectator ions. Therefore, the net ionic equation involves only the carbonate ions and water molecules. \( CO3^{2-} + H2O \rightarrow HCO3^- + OH^- \)

b. Ammonium Bromide

Step 1: Identify the ions Ammonium bromide (NH4Br) dissociates into ammonium ions (NH4+) and bromide ions (Br-) when dissolved in water. Step 2: Write the formula equation Reaction of ammonium ions with water: \( NH4^+ + H2O \rightarrow NH3 + H3O^+ \) Step 3: Write the net ionic equation Since the bromide ions do not participate in the reaction, they are considered as spectator ions. Therefore, the net ionic equation involves only the ammonium ions and water molecules. \( NH4^+ + H2O \rightarrow NH3 + H3O^+ \)

Key concepts

Sodium Carbonate

Sodium carbonate is a white, odorless powder that is commonly used in household cleaning products and in the manufacturing of glass and textiles. When sodium carbonate (\(\text{Na}_2\text{CO}_3\)) dissolves in water, it undergoes hydrolysis. This process involves the breakdown of sodium carbonate into its ionic components.

• The dissociation in water results in sodium ions (\(\text{Na}^+\)) and carbonate ions (\(\text{CO}_3^{2-}\)).
• In a hydrolysis reaction, the carbonate ion reacts with water to produce bicarbonate (\(\text{HCO}_3^-\)) and hydroxide ions (\(\text{OH}^-\)).

This reaction raises the pH of the solution, making it basic. The sodium ions in this reaction act as spectator ions. They do not participate in the chemical change; they merely balance the charge in the solution.

Ammonium Bromide

Ammonium bromide is a salt formed from ammonia and hydrobromic acid. It is used in photography and as a flame retardant. When ammonium bromide (\(\text{NH}_4\text{Br}\)) is dissolved in water, it dissociates into ammonium ions (\(\text{NH}_4^+\)) and bromide ions (\(\text{Br}^-\)).

• In the hydrolysis of ammonium ions with water, the reaction produces ammonia (\(\text{NH}_3\)) and hydronium ions (\(\text{H}_3\text{O}^+\)).

This hydrolysis produces an acidic solution as the concentration of hydronium ions increases. Bromide ions do not partake in the reaction, serving purely as spectator ions.

Net Ionic Equations

Net ionic equations are fundamental for understanding the actual chemical transformations occurring in solutions. They simplify reactions by omitting the spectator ions and focusing on species that undergo change.

• For instance, in the hydrolysis of sodium carbonate, the net ionic equation directly shows carbonate ions reacting with water.
• Similarly, the net ionic equation for ammonium bromide hydrolysis features ammonium ions reacting with water.

By stripping away the extraneous ions, these equations provide a cleaner view of the actual chemistry taking place.

Dissociation

Dissociation refers to the splitting of a compound into its ions when dissolved in water. This is an essential step in determining which ions are involved in a reaction.

• For sodium carbonate, the dissociation process involves forming\(\text{Na}^+\) and\(\text{CO}_3^{2-}\) ions.
• Ammonium bromide dissociates into\(\text{NH}_4^+\) and\(\text{Br}^-\) ions.

Understanding dissociation helps us identify potential interactions between ions and the resulting products of such reactions.

Spectator Ions

Spectator ions are ions that remain unchanged on both the reactant and product sides of a chemical equation. In a hydrolysis reaction, they help maintain charge balance but do not participate in the actual chemical changes that occur.

• For sodium carbonate, sodium ions (\(\text{Na}^+\)) are the spectator ions because they do not engage in the reaction with water.
• Similarly, for ammonium bromide, bromide ions (\(\text{Br}^-\)) serve as spectator ions as they remain unaltered during the reaction.

Knowing which ions are spectators allows for the simplification of equations, highlighting the essential chemistry behind the process.