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Chapter 11: Problem 42

The high melting points of ionic solids indicate that a lot of energy must be supplied to separate the ions from one another. How is it possible that the ions can separate from one another when soluble ionic compounds are dissolved in water, often with essentially no temperature change?

Short Answer

Expert verified
Soluble ionic compounds can dissolve in water without a significant temperature change because the energy released during the hydration process, where water molecules surround and interact with the ions, compensates for the energy needed to break the strong ionic bonds within the lattice structure. The water molecules play a crucial role in weakening the electrostatic forces between the ions, allowing them to separate from each other.

Step by step solution

01

Understand the melting process of ionic solids

Ionic solids have a lattice structure with positive and negative ions held together by ionic bonds. The high melting points of these solids are an indication of the strong electrostatic forces between the ions. In order to melt an ionic compound, a significant amount of energy is required to overcome these forces and separate the ions from the lattice structure.
02

Analyze the dissolving process of ionic compounds in water

When ionic compounds dissolve in water, the ions separate from each other and are surrounded by water molecules. This process is called hydration. The water molecules form a shell around each ion, with the oxygen atom of the water molecule (which has a partial negative charge) oriented towards the positively charged ion, and the hydrogen atoms (with partial positive charges) oriented towards the negatively charged ion. This interaction between water molecules and ions weakens the electrostatic forces between the ions and allows them to separate from each other.
03

Compare the energy changes in the dissolving process with the melting process

During the dissolving process, energy is required to break the ionic bonds between the ions in the solid lattice, but energy is also released when the ions interact with the water molecules and become hydrated. If the energy released during the hydration process is sufficient to compensate for the energy required to break the ionic bonds, the dissolving process can occur without a significant temperature change.
04

Explain why some ionic compounds dissolve without a temperature change

In the case of soluble ionic compounds, the energy released during the hydration process is able to balance the energy required to break the ionic bonds. This is why these compounds can dissolve in water without essentially any temperature change. In conclusion, soluble ionic compounds are able to dissolve in water without a significant temperature change because the energy released during the hydration process compensates for the energy needed to break the ionic bonds within the lattice structure. The water molecules play a crucial role in weakening the electrostatic forces between the ions and allowing them to separate from each other.

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Most popular questions from this chapter

How would you prepare \(1.0 \mathrm{~L}\) of an aqueous solution of sodium chloride having an osmotic pressure of 15 atm at \(22^{\circ} \mathrm{C}\) ? Assume sodium chloride exists as \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) ions in solution.

What volume of a \(0.580-M\) solution of \(\mathrm{CaCl}_{2}\) contains \(1.28 \mathrm{~g}\) solute?

Assume that you place a freshwater plant into a saltwater solution and examine it under a microscope. What happens to the plant cells? What if you placed a saltwater plant in pure water? Explain. Draw pictures to illustrate your explanations.

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a. Calculate the freezing-point depression and osmotic pressure at \(25^{\circ} \mathrm{C}\) of an aqueous solution containing 1.0 \(\mathrm{g} / \mathrm{L}\) of a protein (molar mass \(=9.0 \times 10^{4} \mathrm{~g} / \mathrm{mol}\) ) if the density of the solution is \(1.0 \mathrm{~g} / \mathrm{cm}^{3}\). b. Considering your answer to part a, which colligative property, freezing- point depression or osmotic pressure, would be better used to determine the molar masses of large molecules? Explain.
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