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Ch.13 - Solutions & Their Properties
All textbooksMcMurry 8th EditionCh.13 - Solutions & Their PropertiesProblem 38
Chapter 13, Problem 38

Which would you expect to have the larger (more negative) hydration energy: K+ or Ba2+?

Verified step by step guidance
1
Step 1: Understand the concept of hydration energy. Hydration energy is the energy released when ions are surrounded by water molecules. It is generally more negative for ions with higher charge and smaller ionic radius.
Step 2: Compare the charges of the ions. K+ has a charge of +1, while Ba2+ has a charge of +2. Higher charge typically leads to a more negative hydration energy because the ion can attract more water molecules.
Step 3: Consider the ionic radii. K+ has a larger ionic radius compared to Ba2+. Smaller ions can be more effectively surrounded by water molecules, leading to a more negative hydration energy.
Step 4: Analyze the effect of charge density. Ba2+ has a higher charge density than K+ due to its higher charge and smaller size, which generally results in a more negative hydration energy.
Step 5: Conclude that Ba2+ is expected to have a larger (more negative) hydration energy than K+ due to its higher charge and smaller ionic radius, which enhance its interaction with water molecules.

Key Concepts

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

Hydration Energy

Hydration energy refers to the energy released when ions are surrounded by water molecules. It is a crucial factor in determining how well an ion dissolves in water. The more negative the hydration energy, the more favorable the interaction between the ion and water, leading to greater solubility.
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Charge Density

Charge density is defined as the amount of charge per unit volume around an ion. Ions with higher charge densities, such as Ba2+, exert a stronger electrostatic attraction on water molecules, leading to more significant hydration energy. This concept helps explain why smaller, highly charged ions typically have larger (more negative) hydration energies.
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Ionic Size

Ionic size plays a critical role in determining hydration energy. Smaller ions, like K+, have a lower charge density compared to larger ions like Ba2+. As a result, larger ions can attract more water molecules and stabilize them more effectively, resulting in a more negative hydration energy for the larger ion.
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Related Practice
Textbook Question
If a single 5-g block of NaCl is placed in water, it dissolves slowly, but if 5 g of powdered NaCl is placed in water, it dis- solves rapidly. Explain.
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Which would you expect to have the larger hydration energy, SO42- or ClO4-? Explain.
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Classify the strongest type of intermolecular force in the follow- ing interactions: solvent–solvent, solvent–solute, and solute– solute when solid iodine 1I22 is placed in the water. Based on these interactions, predict whether I2 is soluble in water.