Determine whether each cation is acidic or pH-neutral. For each cation that is acidic, write an equation that shows how the cation acts as an acid. a. Sr²⁺ b. Mn³⁺ c. C₅H₅NH⁺

Verified step by step guidance

1. Step 1: Understand the concept of acidic and pH-neutral cations. Acidic cations are typically those that can donate a proton (H+) or increase the concentration of H+ in solution, often by reacting with water. pH-neutral cations do not affect the pH of the solution significantly.
2. Step 2: Analyze Sr^{2+}. Strontium ion (Sr^{2+}) is a Group 2 metal cation. Group 2 metal cations are generally considered pH-neutral because they do not hydrolyze in water to produce H+ ions.
3. Step 3: Analyze Mn^{3+}. Manganese(III) ion (Mn^{3+}) is a transition metal cation. Transition metal cations with a high positive charge can act as acids by hydrolyzing in water. Write the hydrolysis equation: Mn^{3+} + H_2O \rightarrow Mn(OH)^{2+} + H^+.
4. Step 4: Analyze C_5H_5NH^+. Pyridinium ion (C_5H_5NH^+) is the conjugate acid of pyridine (C_5H_5N). It can donate a proton to water, making it acidic. Write the equation: C_5H_5NH^+ + H_2O \rightarrow C_5H_5N + H_3O^+.
5. Step 5: Summarize the findings. Sr^{2+} is pH-neutral, Mn^{3+} is acidic and hydrolyzes to produce H^+, and C_5H_5NH^+ is acidic and donates a proton to form hydronium ion (H_3O^+).

Key Concepts

Acidic Cations

Acidic cations are positively charged ions that can donate protons (H+) in solution, thereby lowering the pH. These cations typically arise from metals with high charge density, which can polarize water molecules and facilitate the release of protons. Understanding the nature of these cations is crucial for determining their acidic behavior in aqueous solutions.

pH and Neutrality

pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or basicity. A pH of 7 is considered neutral, while values below 7 indicate acidity and above 7 indicate basicity. Cations that do not significantly affect the concentration of H+ ions in solution are classified as pH-neutral, meaning they do not alter the pH of the solution.

Equilibrium and Acid-Base Reactions

Acid-base reactions often involve the transfer of protons between species, establishing an equilibrium between reactants and products. For acidic cations, the reaction can be represented by an equation showing the cation donating a proton to water, forming hydronium ions (H3O+). Understanding this equilibrium is essential for predicting the behavior of cations in solution.