Chapter 12: Problem 84

Certainly if NaCl dissolved in liquid hexane, \(\mathrm{C}_{6} \mathrm{H}_{14}\), the entropy associated with the \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) ions would increase. Nevertheless, \(\mathrm{NaCl}\) does not dissolve in hexane. Why not?

Short Answer

Expert verified

Despite the increase in entropy associated with Na⁺ and Cl⁻ ions, NaCl does not dissolve in liquid hexane because of the principle "like dissolves like." Hexane, a nonpolar solvent, cannot form strong interactions with the Na⁺ and Cl⁻ ions due to its nonpolar nature and is unable to compensate for the energy needed to break the ionic bonds in the NaCl lattice. \( \) Therefore, NaCl remains insoluble in hexane.

Step by step solution

Consider solubility properties

To begin, let's review the general principle of solubility: "like dissolves like". This means that polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. Ionic compounds, such as NaCl, are considered strongly polar, while hexane, a hydrocarbon, is a nonpolar solvent.

Analyze NaCl properties

NaCl is an ionic compound formed by the ionic bond between the sodium ion (Na⁺) and the chloride ion (Cl⁻). Due to the presence of charged particles, NaCl exhibits strong electrostatic forces between Na⁺ and Cl⁻ ions, known as ionic bonds. These strong forces are responsible for holding the ions together in a crystal lattice structure.

Analyze hexane properties

Hexane, on the other hand, is an organic compound with the chemical formula C₆H₁₄. It is a nonpolar solvent due to its structure and the presence of only carbon and hydrogen atoms connected by nonpolar covalent bonds. Nonpolar solvents have no net charge or dipoles and cannot form strong interactions with polar solutes like ionic compounds.

Evaluate interactions for dissolution

For NaCl to dissolve in hexane, the electrostatic forces between Na⁺ and Cl⁻ ions must be overcome. However, hexane, being a nonpolar solvent, does not have the ability to form strong interactions with the Na⁺ and Cl⁻ ions. It cannot stabilize the ions in the solution or compensate for the energy required to break the ionic bonds in the NaCl lattice.

Conclusion

Due to the principle of "like dissolves like" and the inability of hexane to form strong interactions with the Na⁺ and Cl⁻ ions, NaCl does not dissolve in liquid hexane. The increase in entropy associated with the Na⁺ and Cl⁻ ions is not enough to overcome the energy required to break the ionic bonds in NaCl or to form new stabilizing interactions with the nonpolar hexane molecules.

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Certainly if NaCl dissolved in liquid hexane, \(\mathrm{C}_{6} \mathrm{H}_{14}\), the entropy associated with the \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) ions would increase. Nevertheless, \(\mathrm{NaCl}\) does not dissolve in hexane. Why not?

Short Answer

Step by step solution

Consider solubility properties

Analyze NaCl properties

Analyze hexane properties

Evaluate interactions for dissolution

Conclusion

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