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Chapter 13: Problem 14

Indicate whether each statement is true or false: \((\) a) \(\mathrm{NaCl}\) dissolves in water but not in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) because benzene is denser than water. (b) NaCl dissolves in water but not in benzene because water has a large dipole moment and benzene has zero dipole moment. (c) NaCl dissolves in water but not in benzene because the water-ion interactions are stronger than benzene-ion interactions.

Short Answer

Expert verified
(a) False, (b) True, (c) True. The solubility of NaCl depends on the interactions between the solute and the solvent, not their densities. NaCl dissolves in polar solvents like water due to its large dipole moment, and strong water-ion interactions. It does not dissolve in nonpolar solvents like benzene with zero dipole moment and weak benzene-ion interactions.

Step by step solution

01

Statement A: NaCl dissolves in water but not in benzene because benzene is denser than water.

This statement is false because the solubility of NaCl in a solvent depends on the interactions between the solute (NaCl) and the solvent (water or benzene), not on the density of the solvent.
02

Statement B: NaCl dissolves in water but not in benzene because water has a large dipole moment and benzene has zero dipole moment.

This statement is true. NaCl is an ionic compound, so it dissolves in polar solvents like water, which have a large dipole moment. Benzene, being a nonpolar solvent with zero dipole moment, cannot dissolve NaCl due to lack of strong interactions between the ions of NaCl and benzene molecules.
03

Statement C: NaCl dissolves in water but not in benzene because the water-ion interactions are stronger than benzene-ion interactions.

This statement is also true. In order for NaCl to dissolve in a solvent, the solvent-solute interactions must be strong enough to overcome the ionic bonds in NaCl. In water, the strong water-ion interactions, due to hydrogen bonding, are capable of breaking the ionic bonds in NaCl and allowing it to dissolve. However, in benzene, the interactions between the benzene molecules and the ions in NaCl are weak, so NaCl does not dissolve.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Dipole Moment
A dipole moment is a measure of the polarity of a chemical bond within a molecule. It occurs when there is an unequal distribution of electrons between two atoms in a bond, leading to one end being slightly more positive and the other more negative. This polarity arises because different atoms have different electronegativities 鈥� the ability to attract electrons.

For instance, in water (\(\text{H}_2\text{O}\)), the oxygen atom is more electronegative than the hydrogen atoms. This makes the region around the oxygen atom more negatively charged, giving water a significant dipole moment. This characteristic is essential for water's ability to dissolve many substances, like ionic compounds.
  • High dipole moment: indicates a strong polarity
  • Zero dipole moment: means no polarity, as seen in molecules like benzene (\(\text{C}_6\text{H}_6\))
Ionic Compounds
Ionic compounds are formed when atoms transfer electrons to achieve a full outer shell of electrons, resulting in the formation of charged ions. These ions are held together by ionic bonds, which are the strong electrostatic forces of attraction between the oppositely charged ions.

Typical examples include common table salt, \(\text{NaCl}\), where sodium (\(\text{Na}^+\)) and chloride (\(\text{Cl}^-\)) ions bond together. In order for these compounds to dissolve, the solvent must be able to disrupt these strong ionic bonds. Water is particularly good at this due to its polar nature and ability to form strong ion-dipole interactions.
  • Made up of charged ions
  • Generally have high melting and boiling points
  • Conduct electricity when molten or dissolved in water
Polar Solvents
Polar solvents, such as water, are liquids that have molecules with significant electric dipole moments. This means they have partially charged regions within the molecule, contributing to their high polarity. Such solvents are excellent at dissolving ionic compounds because they can surround and stabilize the ions.

Water is the quintessential polar solvent, known for its ability to dissolve a wide range of salts, acids, and other ionic substances. This is because water molecules can form hydrogen bonds and effectively compete with the ionic bonds in compounds like \(\text{NaCl}\), separating the ions and allowing them to disperse in solution.
  • Can dissolve ionic and polar solutes
  • Examples include water, methanol, and ethanol
  • Effective at affecting reactions involving charged species
Nonpolar Solvents
Nonpolar solvents are liquids that consist of molecules without a significant dipole moment, meaning they lack the charged regions found in polar substances. This makes them ineffective at dissolving ionic compounds, such as \(\text{NaCl}\), which depend on strong ion-dipole interactions for dissolution.

Benzene is a classic example of a nonpolar solvent. It has a symmetrical ring structure and evenly distributed electron clouds, reducing the chance of forming dipoles.
  • Poor at dissolving ionic substances but effective for nonpolar solutes
  • Include solvents like benzene, hexane, and toluene
  • Often used in organic chemistry to dissolve grease, oils, and other nonpolar compounds

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Most popular questions from this chapter

You make two solutions of a nonvolatile solute with a liquid solvent, \(0.01 \mathrm{M}\) and \(1.00 \mathrm{M}\). Indicate whether each of the following statements is true or false. (a) The vapor pressure of the concentrated solution is higher than that of the diluted solution. (b) The osmotic pressure of the concentrated solution is higher than that of the diluted solution. (c) The boiling point of the concentrated solution is higher than that of the diluted solution. (d) The freezing point of the concentrated solution is higher than that of the diluted solution.

Proteins can be precipitated out of aqueous solution by the addition of an electrolyte; this process is called "salting out" the protein. (a) Do you think that all proteins would be precipitated out to the same extent by the same concentration of the same electrolyte? (b) If a protein has been salted out, are the protein-protein interactions stronger or weaker than they were before the electrolyte was added? (c) A friend of yours who is taking a biochemistry class says that salting out works because the waters of hydration that surround the protein prefer to surround the electrolyte as the electrolyte is added; therefore, the protein's hydration shell is stripped away, leading to protein precipitation. Another friend of yours in the same biochemistry class says that salting out works because the incoming ions adsorb tightly to the protein, making ion pairs on the protein surface, which end up giving the protein a zero net charge in water and therefore leading to precipitation. Discuss these two hypotheses. What kind of measurements would you need to make to distinguish between these two hypotheses?

Consider two ionic solids, both composed of singly charged ions, that have different lattice energies. (a) Will the solids have the same solubility in water? (b) If not, which solid will be more soluble in water, the one with the larger lattice energy or the one with the smaller lattice energy? Assume that solute-solvent interactions are the same for both solids. [Section 13.1]

Compounds like sodium stearate, called "surfactants" in general, can form structures known as micelles in water, once the solution concentration reaches the value known as the critical micelle concentration (cmc). Micelles contain dozens to hundreds of molecules. The cmc depends on the substance, the solvent, and the temperature. At and above the \(\mathrm{cmc}\), the properties of the solution vary drastically. (a) The turbidity (the amount of light scattering) of solutions increases dramatically at the \(\mathrm{cmc}\). Suggest an explanation. (b) The ionic conductivity of the solution dramatically changes at the \(\mathrm{cmc}\). Suggest an explanation. (c) Chemists have developed fluorescent dyes that glow brightly only when the dye molecules are in a hydrophobic environment. Predict how the intensity of such fluorescence would relate to the concentration of sodium stearate as the sodium stearate concentration approaches and then increases past the \(\mathrm{cmc}\).

(a) What is the mass percentage of iodine in a solution containing \(0.035 \mathrm{~mol} \mathrm{I}_{2}\) in \(125 \mathrm{~g}\) of \(\mathrm{CCl}_{4} ?\) (b) Seawater contains \(0.0079 \mathrm{~g}\) of \(\mathrm{Sr}^{2+}\) per kilogram of water. What is the concentration of \(\mathrm{Sr}^{2+}\) in ppm?
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