Chapter 3: Problem 78
Write net ionic equations for the following reactions: (a) The reaction of acetic acid, a weak acid, and \(\mathrm{Sr}(\mathrm{OH})_{2}(\mathrm{aq})\) (b) The reaction of zinc and hydrochloric acid to form zinc(II) chloride and hydrogen gas.
Short Answer
Expert verified
(a) \(\text{CH}_3\text{COOH}(aq) + 2\text{OH}^-(aq) \rightarrow 2\text{CH}_3\text{COO}^-(aq) + \text{H}_2\text{O}(l)\)
(b) \(\text{Zn}(s) + 2\text{H}^+(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{H}_2(g)\)
Step by step solution
01
Write the Balanced Molecular Equations
(a) For the reaction between acetic acid (weak acid) and strontium hydroxide in aqueous solution:\[\text{CH}_3\text{COOH}(aq) + \text{Sr(OH)}_2(aq) \rightarrow \text{Sr(CH}_3\text{COO)}_2(aq) + \text{H}_2\text{O}(l)\](b) For the reaction of zinc and hydrochloric acid:\[\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)\]
02
Break Down the Compounds into Ions (Complete Ionic Equations)
(a) Acetic acid is a weak acid and doesn’t dissociate completely, while strontium hydroxide is a strong base:\[\text{CH}_3\text{COOH}(aq) + \text{Sr}^{2+}(aq) + 2\text{OH}^-(aq) \rightarrow \text{Sr}^{2+}(aq) + 2\text{CH}_3\text{COO}^-(aq) + \text{H}_2\text{O}(l)\](b) Convert hydrochloric acid and zinc chloride into ions:\[\text{Zn}(s) + 2\text{H}^+(aq) + 2\text{Cl}^-(aq) \rightarrow \text{Zn}^{2+}(aq) + 2\text{Cl}^-(aq) + \text{H}_2(g)\]
03
Identify and Cancel Spectator Ions
(a) In the reaction between acetic acid and strontium hydroxide, the spectator ion is \( \text{Sr}^{2+} \), which appears on both sides:\[\text{CH}_3\text{COOH}(aq) + 2\text{OH}^-(aq) \rightarrow 2\text{CH}_3\text{COO}^-(aq) + \text{H}_2\text{O}(l)\](b) In the zinc and hydrochloric acid reaction, the chloride ions \( \text{Cl}^- \) are spectator ions:\[\text{Zn}(s) + 2\text{H}^+(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{H}_2(g)\]
04
Write the Net Ionic Equations
(a) The net ionic equation for the reaction of acetic acid and strontium hydroxide is:\[\text{CH}_3\text{COOH}(aq) + 2\text{OH}^-(aq) \rightarrow 2\text{CH}_3\text{COO}^-(aq) + \text{H}_2\text{O}(l)\](b) The net ionic equation for the reaction of zinc and hydrochloric acid is:\[\text{Zn}(s) + 2\text{H}^+(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{H}_2(g)\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Acetic Acid
Acetic acid, a chemical compound with the formula \( \text{CH}_3\text{COOH} \), is one of the simplest carboxylic acids and is a key component of vinegar. In chemistry, it is known as a weak acid because it does not completely dissociate into its ions in water. Instead, it partially ionizes to form acetate ions (\( \text{CH}_3\text{COO}^- \)) and hydrogen ions (\( \text{H}^+ \)).
Acetic acid's partial ionization is crucial to understanding reactions involving weak acids. When it reacts with a strong base, like strontium hydroxide, it primarily forms water and acetate ions, making it essential to capture this in the net ionic equation. The equation illustrates how acetic acid interacts minimally with a strong base, providing a model of what occurs when acids do not fully dissociate.
The importance of recognizing weak acids lies in their subdued reactivity, requiring comprehensive understanding, especially when writing net ionic equations, which highlight the dynamic ions involved while excluding spectator ions that don't partake in the chemical change.
Acetic acid's partial ionization is crucial to understanding reactions involving weak acids. When it reacts with a strong base, like strontium hydroxide, it primarily forms water and acetate ions, making it essential to capture this in the net ionic equation. The equation illustrates how acetic acid interacts minimally with a strong base, providing a model of what occurs when acids do not fully dissociate.
The importance of recognizing weak acids lies in their subdued reactivity, requiring comprehensive understanding, especially when writing net ionic equations, which highlight the dynamic ions involved while excluding spectator ions that don't partake in the chemical change.
Strontium Hydroxide
Strontium hydroxide, \( \text{Sr(OH)}_2 \), is a strong base commonly used in chemistry for its complete ionization in water. Unlike weak acids, strong bases such as strontium hydroxide dissociate completely into strontium ions (\( \text{Sr}^{2+} \)) and hydroxide ions (\( \text{OH}^- \)).
When strontium hydroxide reacts with a weak acid like acetic acid, its fully dissociated hydroxide ions interact with the hydrogen ions from acetic acid, resulting in the formation of water. Strontium ions, however, typically remain unreacted, acting as spectator ions that do not partake in the actual chemical reaction.
This ability to dissociate completely makes strontium hydroxide an excellent example of a strong base in net ionic equations. In these sorts of equations, the focus is on the ions that actively participate in the acid-base reaction. Understanding its dissociation is crucial for accurately identifying spectators and understanding the key ions contributing to the chemical transformation.
When strontium hydroxide reacts with a weak acid like acetic acid, its fully dissociated hydroxide ions interact with the hydrogen ions from acetic acid, resulting in the formation of water. Strontium ions, however, typically remain unreacted, acting as spectator ions that do not partake in the actual chemical reaction.
This ability to dissociate completely makes strontium hydroxide an excellent example of a strong base in net ionic equations. In these sorts of equations, the focus is on the ions that actively participate in the acid-base reaction. Understanding its dissociation is crucial for accurately identifying spectators and understanding the key ions contributing to the chemical transformation.
Zinc and Hydrochloric Acid
The reaction between zinc (\( \text{Zn} \)) and hydrochloric acid (\( \text{HCl} \)) is an example of a redox reaction. Here, zinc, a solid metal, reacts with the hydrogen ions from hydrochloric acid to form zinc ions (\( \text{Zn}^{2+} \)) and hydrogen gas (\( \text{H}_2 \)).
The hydrochloric acid dissociates completely in solutions releasing hydrogen ions (\( \text{H}^+ \)) and chloride ions (\( \text{Cl}^- \)). However, only the hydrogen ions actively participate in the reaction with zinc, as chloride ions do not change and remain as spectator ions.
This reaction demonstrates a displacement process where zinc replaces hydrogen, leading to the release of hydrogen gas. Writing its net ionic equation showcases the reduction of hydrogen ions to hydrogen gas without the interference of chloride ions. This simplification helps students focus on the actual redox transformation happening between zinc and the hydrogen component of hydrochloric acid.
The hydrochloric acid dissociates completely in solutions releasing hydrogen ions (\( \text{H}^+ \)) and chloride ions (\( \text{Cl}^- \)). However, only the hydrogen ions actively participate in the reaction with zinc, as chloride ions do not change and remain as spectator ions.
This reaction demonstrates a displacement process where zinc replaces hydrogen, leading to the release of hydrogen gas. Writing its net ionic equation showcases the reduction of hydrogen ions to hydrogen gas without the interference of chloride ions. This simplification helps students focus on the actual redox transformation happening between zinc and the hydrogen component of hydrochloric acid.
Weak Acid and Strong Base Reaction
Understanding the reaction between a weak acid and a strong base involves recognizing the nuances of incomplete ionization by weak acids and complete ionization by strong bases. A classic example of this is the reaction between acetic acid (weak acid) and strontium hydroxide (strong base).
In a typical weak acid and strong base reaction, the hydrogen ions provided by the weak acid combine with the hydroxide ions from the strong base to produce water. The ions that result from this are often spectator ions. In the acetic acid and strontium hydroxide reaction, the essential players are the acetate ions and hydroxide ions, as strontium ions are not chemically altered during the reaction.
What is critical for students to understand is that the distinction between weak and strong acids or bases significantly impacts the net ionic equations. The key to mastering this concept is to focus on the ions that change during the reaction while excluding those that do not, which streamlines the learning of chemical reactivity and equation formation.
In a typical weak acid and strong base reaction, the hydrogen ions provided by the weak acid combine with the hydroxide ions from the strong base to produce water. The ions that result from this are often spectator ions. In the acetic acid and strontium hydroxide reaction, the essential players are the acetate ions and hydroxide ions, as strontium ions are not chemically altered during the reaction.
What is critical for students to understand is that the distinction between weak and strong acids or bases significantly impacts the net ionic equations. The key to mastering this concept is to focus on the ions that change during the reaction while excluding those that do not, which streamlines the learning of chemical reactivity and equation formation.