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Chapter 10: Problem 24

In order for sodium chloride to dissolve in water, a small amount of energy must be added during solution formation. This is not energetically favorable. Why is NaCl so soluble in water?

Short Answer

Expert verified
Sodium chloride (NaCl) is soluble in water due to the polar nature of water molecules and the formation of ion-dipole interactions between Na+ and Cl- ions and water molecules. Although energy is required to break the ionic bonds in NaCl (endothermic process), the exothermic hydration energy released during the formation of ion-dipole interactions is sufficient to overcome this energy requirement, resulting in a net decrease in energy and making NaCl dissolution energetically favorable.

Step by step solution

01

Understand the components involved in the process

Sodium chloride, which is a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-), is an ionic compound. Water, on the other hand, is a polar molecule with a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom.
02

Describe the energetic process during dissolution

In order for sodium chloride to dissolve in water, the ionic bonds between the Na+ and Cl- ions must be broken, which requires the input of energy. This process is endothermic and therefore not energetically favorable on its own.
03

Explain the role of water molecules in the dissolution process

Due to the polar nature of water molecules, they have a tendency to attract charged particles, such as the positively charged Na+ and negatively charged Cl- ions in sodium chloride. When water molecules come into contact with sodium chloride, the partial positive charge on the hydrogen atoms in water is attracted to the negatively charged chloride ions, whereas the partial negative charge on the oxygen atom in water is attracted to the positively charged sodium ions. These attractions between water molecules and sodium chloride ions create ion-dipole interactions that help to overcome the ionic bonds holding sodium chloride together.
04

Describe the energetic changes during the dissolution process

As sodium chloride dissolves in water, energy is released due to the formation of ion-dipole interactions between water molecules and Na+ and Cl- ions. The energy released during this process is called hydration energy, and it is exothermic. The net energy change during the dissolution process is determined by the balance between the endothermic process of breaking ionic bonds and the exothermic process of forming ion-dipole interactions.
05

Explain why NaCl is so soluble in water despite the energy requirement

The reason why sodium chloride is so soluble in water is because the exothermic hydration energy released during the formation of favorable ion-dipole interactions between the Na+ and Cl- ions and water molecules is sufficient to overcome the endothermic energy required to break the ionic bonds in sodium chloride. This results in a net decrease in energy, making the dissolution process energetically favorable.

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Most popular questions from this chapter

Erythrocytes are red blood cells containing hemoglobin. In a saline solution they shrivel when the salt concentration is high and swell when the salt concentration is low. In a \(25^{\circ} \mathrm{C}\) aqueous solution of \(\mathrm{NaCl}\), whose freezing point is \(-0.406^{\circ} \mathrm{C},\) erythrocytes neither swell nor shrink. If we want to calculate the osmotic pressure of the solution inside the erythrocytes under these conditions, what do we need to assume? Why? Estimate how good (or poor) of an assumption this is. Make this assumption and calculate the osmotic pressure of the solution inside the erythrocytes.

The lattice energy of \(\mathrm{NaCl}\) is \(-786 \mathrm{kJ} / \mathrm{mol}\), and the enthalpy of hydration of 1 mole of gaseous \(\mathrm{Na}^{+}\) and 1 mole of gaseous \(\mathrm{Cl}^{-}\) ions is \(-783 \mathrm{kJ} / \mathrm{mol} .\) Calculate the enthalpy of solution per mole of solid NaCl.

The freezing point of \(t\) -butanol is \(25.50^{\circ} \mathrm{C}\) and \(K_{\mathrm{f}}\) is \(9.1^{\circ} \mathrm{C} \cdot \mathrm{kg} /\) mol. Usually \(t\) -butanol absorbs water on exposure to air. If the freezing point of a 10.0 -g sample of \(t\) -butanol is \(24.59^{\circ} \mathrm{C},\) how many grams of water are present in the sample?

An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass percents of \(31.57 \%\) C and \(5.30 \%\) H. The molar mass is determined by measuring the freezing-point depression of an aqueous solution. A freezing point of \(-5.20^{\circ} \mathrm{C}\) is recorded for a solution made by dissolving \(10.56 \mathrm{g}\) of the compound in \(25.0 \mathrm{g}\) water. Determine the empirical formula, molar mass, and molecular formula of the compound. Assume that the compound is a nonelectrolyte.

Using the phase diagram for water and Raoult's law, explain why salt is spread on the roads in winter (even when it is below freezing).
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