Question

Explain why the net ionic equation for the neutralization reaction between \(\mathrm{HCl}(\mathrm{aq})\) and \(\mathrm{KOH}(\mathrm{aq})\) is the same as the net ionic equation for the neutralization reaction between \(\mathrm{HNO}_{3}(\mathrm{aq})\) and \(\mathrm{RbOH}\).

Short answer

The net ionic equation is \( \mathrm{H^+} + \mathrm{OH^-} \rightarrow \mathrm{H_2O} \) because only \( \mathrm{H^+} \) and \( \mathrm{OH^-} \) react, with other ions being spectators.

Step-by-step solution

Identify Reactants and Products

In the reaction between HCl(aq) and KOH(aq), the reactants are hydrochloric acid and potassium hydroxide. For the reaction between HNO₃(aq) and RbOH(aq), the reactants are nitric acid and rubidium hydroxide. Both reactions are acid-base neutralization reactions, producing water and a salt as products.

Write Molecular Equations

For the first reaction: \( \mathrm{HCl} + \mathrm{KOH} \rightarrow \mathrm{H_2O} + \mathrm{KCl} \). For the second reaction: \( \mathrm{HNO_3} + \mathrm{RbOH} \rightarrow \mathrm{H_2O} + \mathrm{RbNO_3} \). Both produce water and a salt.

Split into Ionic Equations

Write the ionic equations for both reactions. For reaction 1: \( \mathrm{H^+} + \mathrm{Cl^-} + \mathrm{K^+} + \mathrm{OH^-} \rightarrow \mathrm{K^+} + \mathrm{Cl^-} + \mathrm{H_2O} \). For reaction 2: \( \mathrm{H^+} + \mathrm{NO_3^-} + \mathrm{Rb^+} + \mathrm{OH^-} \rightarrow \mathrm{Rb^+} + \mathrm{NO_3^-} + \mathrm{H_2O} \).

Cancel Spectator Ions

Identify and cancel out the spectator ions, which are ions that appear unchanged on both sides of the equation. In both reactions, \( \mathrm{K^+} \) and \( \mathrm{Cl^-} \) (from the first reaction) and \( \mathrm{Rb^+} \), \( \mathrm{NO_3^-} \) (from the second reaction) are spectator ions. Removing these gives: \( \mathrm{H^+} + \mathrm{OH^-} \rightarrow \mathrm{H_2O} \).

Write the Net Ionic Equation

After canceling the spectator ions, the net ionic equation for both reactions is \( \mathrm{H^+} + \mathrm{OH^-} \rightarrow \mathrm{H_2O} \). This represents the neutralization of an acid by a base and is the same for both reactions.

Key concepts

Neutralization Reaction

A neutralization reaction is a fundamental concept in chemistry, particularly involving acids and bases. It occurs when an acid and a base react with each other to produce water and a salt. This type of reaction helps to balance the pH of a solution. For example, when hydrochloric acid (HCl) reacts with potassium hydroxide (KOH), they produce water (\( \text{H}_2\text{O} \)) and potassium chloride (KCl). Similarly, nitric acid (\(\text{HNO}_3 \)) reacting with rubidium hydroxide (\(\text{RbOH} \)) forms water and rubidium nitrate (\(\text{RbNO}_3 \)).
The general formula for a neutralization reaction can be represented as:

• Acid + Base → Water + Salt

Neutralization reactions are important in many contexts. They are used in laboratory settings to determine the concentration of unknown acids or bases through titration. Beyond the lab, they play a crucial role in industries such as pharmaceuticals and agriculture.

Acid-Base Chemistry

Acid-base chemistry deals with the properties of acids and bases, which are two key concepts in chemistry. Acids are substances that can donate a proton (H⁺), while bases are substances that can accept a proton. When these two react in a water-based solution, they often undergo a neutralization reaction.
Key characteristics of acids include:

• They have a sour taste.
• They turn blue litmus paper red.
• They can donate hydrogen ions (H⁺).

For bases, key features include:

• They have a bitter taste and a slippery feel.
• They turn red litmus paper blue.
• They can donate hydroxide ions (OH⁻).

The interaction of acids and bases in water leads to the formation of water and salts, which are neutral compounds. This is why understanding acid-base chemistry is crucial for making solutions less corrosive and more balanced.

Spectator Ions

In the context of chemical reactions, especially in ionic solutions, spectator ions are ions that do not participate in the actual chemical change but are present in the solution. They appear as both reactants and products in chemical equations but remain unchanged.
For example, when HCl reacts with KOH, the potassium (\(\text{K}^+ \)) and chloride ions (\(\text{Cl}^- \)) are spectator ions because they do not participate in forming the water in the neutralization reaction. Similarly, in the reaction between HNO₃ and RbOH, rubidium (\(\text{Rb}^+ \)) and nitrate ions (\(\text{NO}_3^- \)) act as spectator ions.
It is crucial to recognize and remove spectator ions when writing net ionic equations because:

• They simplify the equations and highlight the actual chemical change.
• They help in understanding the core part of the reaction without unnecessary ions.

Identifying spectator ions is essential in simplifying reactions, allowing chemists to make precise predictions and explanations about a chemical process.