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Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 99d

Indicate whether each of the following statements is correct or incorrect. (d) K+ ion is acidic in water because it causes hydrating water molecules to become more acidic.

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Understand the nature of the K+ ion: Potassium ion (K+) is a cation formed when potassium loses one electron.
Consider the concept of acidity in water: A species is considered acidic if it can donate a proton (H+) to water, increasing the concentration of H3O+ ions.
Evaluate the interaction of K+ with water: K+ is a large, monovalent cation with a low charge density, meaning it does not significantly polarize water molecules.
Analyze the effect of K+ on water acidity: Since K+ does not polarize water molecules effectively, it does not increase the acidity of water by donating protons or causing water to release protons.
Conclude the statement's correctness: Based on the analysis, determine whether the statement about K+ ion being acidic in water is correct or incorrect.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acidity and Basicity

Acidity refers to the ability of a substance to donate protons (H+) in a solution, while basicity refers to the ability to accept protons. In aqueous solutions, acids increase the concentration of H+ ions, which lowers the pH, making the solution more acidic. Understanding these definitions is crucial for evaluating the behavior of ions like K+ in water.
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Hydration of Ions

When ions dissolve in water, they interact with water molecules, forming a hydration shell. This process can influence the properties of the solution, including its acidity. However, the K+ ion, being a cation of a strong base (KOH), does not significantly affect the pH of water, as it does not lead to an increase in H+ concentration.
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Strong vs. Weak Acids and Bases

Strong acids and bases completely dissociate in water, while weak acids and bases do not. The K+ ion originates from potassium hydroxide, a strong base, which means it does not contribute to acidity in solution. Recognizing the strength of acids and bases is essential for determining the behavior of ions in aqueous environments.
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