Problem 110 - Chemistry: An Atoms-Focused Approach

Question

Write the chemical and the net ionic equations describing the reactions that occur when aqueous solutions of these pairs of compounds are mixed together. For each reaction label the Bronsted-Lowry acids and bases. a. HCl and \(\mathrm{Ca}(\mathrm{OH})_{2}\) b. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{KOH}\) c. HNO \(_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) d. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Step-by-Step Solution

Answer

a) HCl and Ca(OH)₂ b) H₃PO₄ and KOH c) HNO₃ and Na₂CO₃ d) H₃PO₄ and Ca(OH)₂ Answer: a) Chemical equation: 2HCl + Ca(OH)₂ → CaCl₂ + 2H₂O, Net ionic equation: H⁺ + OH⁻ → H₂O, Bronsted-Lowry acid: HCl, Bronsted-Lowry base: Ca(OH)₂ b) Chemical equation: H₃PO₄ + 3KOH → K₃[PO₄] + 3H₂O, Net ionic equation: H⁺ + OH⁻ → H₂O, Bronsted-Lowry acid: H₃PO₄, Bronsted-Lowry base: KOH c) Chemical equation: 2HNO₃ + Na₂CO₃ → 2NaNO₃ + H₂O + CO₂, Net ionic equation: 2H⁺ + CO₃²⁻ → H₂O + CO₂, Bronsted-Lowry acid: HNO₃, Bronsted-Lowry base: Na₂CO₃ d) Chemical equation: 2H₃PO₄ + 3Ca(OH)₂ → Ca₃[PO₄]₂ + 6H₂O, Net ionic equation: H⁺ + OH⁻ → H₂O, Bronsted-Lowry acid: H₃PO₄, Bronsted-Lowry base: Ca(OH)₂

Step 1: Identify the Acid and the Base

In this reaction, HCl acts as the acid and \(\mathrm{Ca}(\mathrm{OH})_{2}\) acts as the base.

Step 2: Write the Chemical Equation

The chemical equation for the reaction between HCl and \(\mathrm{Ca}(\mathrm{OH})_{2}\) is: \(2\mathrm{HCl} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{CaCl}_{2} + 2\mathrm{H}_{2}\mathrm{O}\)

Step 3: Write the Net Ionic Equation

The net ionic equation for this reaction is: \(\mathrm{H}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{H}_{2}\mathrm{O}\)

Step 4: Label the Bronsted-Lowry Acids and Bases

In this reaction, HCl is the Bronsted-Lowry acid and \(\mathrm{Ca}(\mathrm{OH})_{2}\) is the Bronsted-Lowry base. b. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{KOH}\)

Step 1: Identify the Acid and the Base

In this reaction, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) acts as the acid and \(\mathrm{KOH}\) acts as the base.

Step 2: Write the Chemical Equation

The chemical equation for the reaction between \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{KOH}\) is: \(\mathrm{H}_{3} \mathrm{PO}_{4} + 3 \mathrm{KOH} \rightarrow \mathrm{K}_{3}[\mathrm{PO}_{4}] + 3\mathrm{H}_{2}\mathrm{O}\)

Step 3: Write the Net Ionic Equation

The net ionic equation for this reaction is: \(\mathrm{H}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{H}_{2}\mathrm{O}\)

Step 4: Label the Bronsted-Lowry Acids and Bases

In this reaction, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) is the Bronsted-Lowry acid and \(\mathrm{KOH}\) is the Bronsted-Lowry base. c. HNO\(_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

Step 1: Identify the Acid and the Base

In this reaction, HNO\(_{3}\) acts as the acid and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) acts as the base.

Step 2: Write the Chemical Equation

The chemical equation for the reaction between HNO\(_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is: \(2\mathrm{HNO_{3}} + \mathrm{Na}_{2} \mathrm{CO}_{3} \rightarrow 2\mathrm{NaNO_{3}} + \mathrm{H}_{2}\mathrm{O} + \mathrm{CO}_{2}\)

Step 3: Write the Net Ionic Equation

The net ionic equation for this reaction is: \(2\mathrm{H}^{+} + \mathrm{CO}_{3}^{2-} \rightarrow \mathrm{H}_{2}\mathrm{O} + \mathrm{CO}_{2}\)

Step 4: Label the Bronsted-Lowry Acids and Bases

In this reaction, HNO\(_{3}\) is the Bronsted-Lowry acid and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is the Bronsted-Lowry base. d. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Step 1: Identify the Acid and the Base

In this reaction, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) acts as the acid and \(\mathrm{Ca}(\mathrm{OH})_{2}\) acts as the base.

Step 2: Write the Chemical Equation

The chemical equation for the reaction between \(\mathrm{H}_{3} \mathrm{PO}_{4}\) and \(\mathrm{Ca}(\mathrm{OH})_{2}\) is: \(2\mathrm{H}_{3} \mathrm{PO}_{4} + 3\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{Ca}_{3}[\mathrm{PO}_{4}]_{2} + 6\mathrm{H}_{2}\mathrm{O}\)

Step 3: Write the Net Ionic Equation

The net ionic equation for this reaction is: \(\mathrm{H}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{H}_{2}\mathrm{O}\)

Step 4: Label the Bronsted-Lowry Acids and Bases

In this reaction, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) is the Bronsted-Lowry acid and \(\mathrm{Ca}(\mathrm{OH})_{2}\) is the Bronsted-Lowry base.

Key Concepts

Chemical Equations

A chemical equation represents a chemical reaction using symbols and formulas. It shows the reactants on the left side and the products on the right, with an arrow pointing from reactants to products.
The coefficients in front of the formulas indicate the number of molecules or moles involved. This ensures mass is conserved during the reaction.

• For example, in the reaction between hydrochloric acid (HCl) and calcium hydroxide (Ca(OH)\(_2\)), the chemical equation is: \[ 2\mathrm{HCl} + \mathrm{Ca(OH)}_2 \rightarrow \mathrm{CaCl}_2 + 2\mathrm{H}_2\mathrm{O} \]
• This equation tells us that two molecules of HCl react with one molecule of Ca(OH)\(_2\) to produce one molecule of CaCl\(_2\) and two molecules of water.

Understanding how to write and balance chemical equations is crucial for describing reactions accurately.

Net Ionic Equations

Net ionic equations focus on the ions directly involved in the chemical reaction, excluding the spectator ions that remain unchanged. This simplifies the reaction by highlighting only the essential components.
For instance, in the reaction between HCl and Ca(OH)\(_2\), the net ionic equation is written as: \[ \mathrm{H}^+ + \mathrm{OH}^- \rightarrow \mathrm{H}_2\mathrm{O} \]

• This equation shows that only the hydrogen ions (H\(^+\)) from the acid and the hydroxide ions (OH\(^-\)) from the base interact to form water.
• Spectator ions like Ca\(^ {2+} \) and Cl\(^-\) are not included in the net ionic equation because they don't change during the reaction.

Writing net ionic equations helps students appreciate the main chemical transformation without the confusion of additional ions.

Acid and Base Identification

Identifying acids and bases in a chemical reaction is essential for understanding how they interact. Acids typically donate hydrogen ions (protons, H\(^+\)), while bases provide hydroxide ions (OH\(^-\)).
Some common criteria for identifying acids and bases include:

• Acids: Substances like HCl and H\(_3\)PO\(_4\) that release H\(^+\) ions when dissolved in water.
• Bases: Compounds such as Na\(_2\)CO\(_3\), KOH, and Ca(OH)\(_2\) that provide OH\(^-\) ions upon dissolution.

By recognizing which components act as acids and bases, students can better predict reaction products and understand the transformation that takes place.

Bronsted-Lowry Theory

The Bronsted-Lowry theory, a key concept in understanding acid-base reactions, describes acids and bases in terms of their ability to donate or accept protons. According to this theory:

• Acids are proton donors. They give up H\(^+\) ions in a reaction.
• Bases are proton acceptors. They receive H\(^+\) ions from the acid.

Taking the example of HCl and Ca(OH)\(_2\), HCl acts as a Bronsted-Lowry acid by donating a proton, whereas Ca(OH)\(_2\) acts as a Bronsted-Lowry base by accepting a proton.
This conceptual framework is crucial for analyzing acid-base reactions beyond mere simple neutralization.