Question

Write balanced ionic equations for the following reactions: (a) Aqueous hydrobromic acid is neutralized by aqueous calcium hydroxide. (b) Aqueous barium hydroxide is neutralized by aqueous nitric acid.

Short answer

(a) H⁺(aq) + OH⁻(aq) → H₂O(l); (b) H⁺(aq) + OH⁻(aq) → H₂O(l).

Step-by-step solution

Write the Complete Molecular Equation for (a)

The reaction between aqueous hydrobromic acid (HBr) and aqueous calcium hydroxide (Ca(OH)₂) results in the formation of water and calcium bromide (CaBr₂). The molecular equation is:\[2 \text{HBr} (aq) + \text{Ca(OH)}_2 (aq) \rightarrow \text{CaBr}_2 (aq) + 2 \text{H}_2\text{O} (l)\]

Write the Complete Ionic Equation for (a)

Now, we will break down all the soluble ionic compounds into their constituent ions:\[2 \text{H}^+ (aq) + 2 \text{Br}^- (aq) + \text{Ca}^{2+} (aq) + 2 \text{OH}^- (aq) \rightarrow \text{Ca}^{2+} (aq) + 2 \text{Br}^- (aq) + 2 \text{H}_2\text{O} (l)\]

Cancel Out Spectator Ions for (a)

Spectator ions appear on both sides of the ionic equation. The spectator ions are \(\text{Ca}^{2+}\) and \(\text{Br}^-\) ions. Cancel them out:\[2 \text{H}^+ (aq) + 2 \text{OH}^- (aq) \rightarrow 2 \text{H}_2\text{O} (l)\]

Simplify the Net Ionic Equation for (a)

Finally, simplify the net ionic equation. Divide all coefficients by 2 to get:\[\text{H}^+ (aq) + \text{OH}^- (aq) \rightarrow \text{H}_2\text{O} (l)\]

Write the Complete Molecular Equation for (b)

For the neutralization of aqueous barium hydroxide \(\text{Ba(OH)}_2\) by aqueous nitric acid \(\text{HNO}_3\), the products formed are water and barium nitrate \(\text{Ba(NO}_3)_2\). The molecular equation is:\[\text{Ba(OH)}_2 (aq) + 2 \text{HNO}_3 (aq) \rightarrow \text{Ba(NO}_3)_2 (aq) + 2 \text{H}_2\text{O} (l)\]

Write the Complete Ionic Equation for (b)

Convert the molecular equation into an ionic one by dissociating all soluble compounds into ions:\[\text{Ba}^{2+} (aq) + 2 \text{OH}^- (aq) + 2 \text{H}^+ (aq) + 2 \text{NO}_3^- (aq) \rightarrow \text{Ba}^{2+} (aq) + 2 \text{NO}_3^- (aq) + 2 \text{H}_2\text{O} (l)\]

Cancel Out Spectator Ions for (b)

Identify and cancel the ions that appear on both sides of the equation, which are \(\text{Ba}^{2+}\) and \(\text{NO}_3^-\) ions:\[2 \text{OH}^- (aq) + 2 \text{H}^+ (aq) \rightarrow 2 \text{H}_2\text{O} (l)\]

Simplify the Net Ionic Equation for (b)

Simplify the resulting net ionic equation by dividing through by 2:\[\text{H}^+ (aq) + \text{OH}^- (aq) \rightarrow \text{H}_2\text{O} (l)\]

Key concepts

Neutralization Reactions

Neutralization reactions are chemical processes where an acid and a base react to form water and a salt. These reactions are crucial in chemistry because they help in understanding how different compounds interact with each other.
In a typical neutralization reaction, hydrogen ions (\(\text{H}^+\)) from the acid combine with hydroxide ions (\(\text{OH}^-\)) from the base to create water (\(\text{H}_2\text{O}\)). This process not only reduces the acidity or basicity of the solution but also can produce a salt, such as calcium bromide (\(\text{CaBr}_2\)) or barium nitrate (\(\text{Ba(NO}_3)_2\)).
Neutralization reactions are useful in many real-world applications:

• Cleaning products often rely on neutralization to target acidic or basic stains.
• Our bodies use neutralization reactions in digestion and blood pH regulation.
• Environmental management uses neutralization to treat acidic rain or waste products.

Understanding these reactions helps in predicting the outcomes and managing reactions in various scientific and industrial processes.

Spectator Ions

In many chemical reactions, not all ions participate directly in the reaction. These non-participating ions are called spectator ions.
Spectator ions are ions that appear unchanged on both sides of a chemical equation. They do not participate in the chemical change and remain in the aqueous solution throughout the reaction process.
Identifying spectator ions is important for simplifying ionic equations. In the given example, for both hydrobromic acid with calcium hydroxide and barium hydroxide with nitric acid reactions, \(\text{Ca}^{2+}\) and \(\text{Ba}^{2+}\) ions are spectator ions since they appear on both sides of the equation without undergoing any transformation.
Recognizing which ions are merely spectators allows chemists to focus on the actual chemical changes occurring in a reaction. This simplification leads to the derivation of the net ionic equation, making it easier to understand the reaction's essence.

Net Ionic Equation

A net ionic equation presents only the ions and molecules directly involved in the chemical reaction, stripping away the spectator ions.
This equation showcases what is most important in the reaction, highlighting the transformation of the involved reactants to their products. For the neutralization reactions given, the net ionic equation for both reactions simplifies to:\(\text{H}^+ (aq) + \text{OH}^- (aq) \rightarrow \text{H}_2\text{O} (l)\). This succinctly shows that the primary reaction is the formation of water from hydrogen and hydroxide ions.
The net ionic equation is especially valuable because it helps chemists understand the true basics of chemical reactivity and stoichiometry without superfluous information.
Creating a net ionic equation involves:

• Writing the balanced molecular equation.
• Breaking it down into the complete ionic equation.
• Identifying and removing spectator ions.

This approach simplifies the study of reactions and provides a more streamlined view of chemical processes.