Question

Which of the following compounds are more soluble in acidic solution than in pure water? Write a balanced net ionic equation for each dissolution reaction. (a) \(\mathrm{MnS}\) (b) \(\mathrm{Fe}(\mathrm{OH})_{3}\) (c) \(\mathrm{AgCl}\) (d) \(\mathrm{BaCO}_{3}\)

Short answer

MnS, Fe(OH)3, and BaCO3 are more soluble in acidic solutions.

Step-by-step solution

Understanding Solubility in Acidic Solutions

Compounds that form weak acids or weak bases upon dissolution tend to be more soluble in acidic solutions. We need to identify if the compound forms an anion that can react with \( ext{H}^+\) or releases \( ext{OH}^-\) ions, which will be neutralized by \( ext{H}^+\) in the acidic solution.

Analyzing MnS Solubility

- \( ext{MnS}\) dissociates as \( ext{Mn}^{2+} + ext{S}^{2-}\).- \( ext{S}^{2-}\) can react with \( ext{H}^+\) in an acidic solution to form \( ext{H}_2 ext{S}\), a gas.- Hence, \( ext{MnS}\) is more soluble in an acidic solution.

Analyzing Fe(OH)3 Solubility

- \( ext{Fe(OH)}_3\) dissociates into \( ext{Fe}^{3+} + 3 ext{OH}^-\).- \( ext{OH}^-\) is neutralized by \( ext{H}^+\) to form water, increasing solubility in an acidic solution.- Thus, \( ext{Fe(OH)}_3\) is more soluble in an acidic solution.

Analyzing AgCl Solubility

- \( ext{AgCl}\) dissociates as \( ext{Ag}^+ + ext{Cl}^-\).- \( ext{Cl}^-\) is a weak conjugate base of a strong acid ( ext{HCl}), and does not react with \( ext{H}^+\).- \( ext{AgCl}\) is not more soluble in an acidic solution.

Analyzing BaCO3 Solubility

- \( ext{BaCO}_3\) dissociates as \( ext{Ba}^{2+} + ext{CO}_3^{2-}\).- \( ext{CO}_3^{2-}\) reacts with \( ext{H}^+\) to form carbonic acid (\( ext{H}_2 ext{CO}_3\)), which decomposes to \( ext{CO}_2\) and water.- Thus, \( ext{BaCO}_3\) is more soluble in an acidic solution.

Writing Net Ionic Equations

- **For \( ext{MnS}\):** \\[ \text{S}^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{S(g)} \]\- **For \( ext{Fe(OH)}_3\):** \\[ 3\text{OH}^- + 3\text{H}^+ \rightarrow 3\text{H}_2\text{O} \]\- **For \( ext{BaCO}_3\):** \\[\text{CO}_3^{2-} + 2\text{H}^+ \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{O} \]\These are the net ionic equations for the substances that dissolve more in acidic solution.

Key concepts

Net Ionic Equations

Net ionic equations provide a simple way of showing the chemical species that actually participate in a reaction. When a substance dissolves in water and reacts in an acidic solution, not all of its ions are involved in the subsequent reactions. Instead, some ions remain unchanged and do not participate. These are known as spectator ions.

To generate a net ionic equation, follow these steps:

• Identify the ions formed when a compound dissociates in water. For instance, \(\mathrm{MnS}\) dissociates into \(\mathrm{Mn}^{2+}\) and \(\mathrm{S}^{2-}\).
• Focus on ions that react with \(\mathrm{H}^{+}\) ions from the acidic solution.
• Eliminate spectator ions that do not participate in the reaction.
• Write the chemical equation reflecting only the actual reactants and products, such as \(\mathrm{S}^{2-} + 2\mathrm{H}^+ \rightarrow \mathrm{H}_2\mathrm{S(g)}\) for the dissolution of \(\mathrm{MnS}\).

Net ionic equations highlight the active components in a reaction, stripping away the unnecessary details for clarity.

Dissolution Reactions

Dissolution reactions involve breaking down a compound into its constituent ions in a solution. When a compound interacts with water, it may dissolve by dissociating into ions, thereby forming an aqueous solution. In the context of solubility in acidic solutions, dissolution may be enhanced by the presence of hydrogen ions.

Several factors affect dissolution reactions in acidic solutions:

• Compounds containing anions that are bases tend to increase solubility in acidic environments because they react with hydrogen ions. For instance, the reaction of \(\mathrm{CO}_3^{2-}\) with \(\mathrm{H}^+\) to form carbonic acid, which further decomposes to \(\mathrm{CO}_2\) and water, enhances the solubility of \(\mathrm{BaCO}_3\).
• For compounds like \(\mathrm{Fe(OH)}_3\), dissolution involves the reaction of \(\mathrm{OH}^-\) with \(\mathrm{H}^+\) to form water, making the solution clearer and increasing solubility in acidic conditions.

Understanding the specific properties of a compound and its potential reactions with \(\mathrm{H}^+\) is crucial for predicting solubility changes in varying pH environments.

Weak Acids and Bases

Weak acids and bases are substances that partially dissociate in solution. This characteristic is essential when considering solubility in different pH environments. For solubility in acids, compounds that form weak acids or bases upon dissolution can be more soluble.

Key points about weak acids and bases:

• Weak acids donate fewer hydrogen ions compared to strong acids, influencing reactions with anions in solution.
• Weak bases do not fully associate with hydrogen ions, impacting their solubility in acidic conditions.
• Anions that form weak acids upon gaining \(\mathrm{H}^+\), such as \(\mathrm{S}^{2-}\) forming \(\mathrm{H}_2\mathrm{S}\), increase solubility because they effectively use available \(\mathrm{H}^+\) ions.

This concept helps us understand why some compounds dissolve more readily in acidic solutions, as it often hinges on the potential to form weak acids or participate in reactions that stabilize the system.