Question

Determine if each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. a. \(\mathrm{CCl}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) b. \(\mathrm{KCl}\) and \(\mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\) d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2} \mathrm{O}\)

Short answer

a. CCl4 and H2O do not form a homogeneous solution. b. KCl and H2O form a homogeneous solution with ion-dipole forces. c. Br2 and CCl4 form a homogeneous solution with London dispersion forces. d. CH3CH2OH and H2O form a homogeneous solution with hydrogen bonding.

Step-by-step solution

- Examine Solubility of CCl4 and H2O

Assess the solubility of carbon tetrachloride (CCl4) in water (H2O). CCl4 is a nonpolar molecule while H2O is polar. Polar and nonpolar substances usually do not mix. A homogeneous solution is not likely.

- Examine Solubility of KCl and H2O

Assess the solubility of potassium chloride (KCl) in water (H2O). KCl is an ionic compound and H2O is a polar solvent. Ionic compounds tend to dissolve well in polar solvents due to ion-dipole forces. Therefore, KCl and H2O do form a homogeneous solution.

- Determine Forces between KCl and H2O

The forces involved between KCl (ionic compound) and H2O (polar solvent) are ion-dipole forces. These forces come from the attraction between the positive (K+) and negative (Cl-) ions of KCl and the partial positive and negative charges of H2O.

- Examine Solubility of Br2 and CCl4

Assess the solubility of bromine (Br2) in carbon tetrachloride (CCl4). Both Br2 and CCl4 are nonpolar molecules. Nonpolar substances generally mix with other nonpolar substances, so they do form a homogeneous solution.

- Determine Forces between Br2 and CCl4

The interaction between two nonpolar molecules like Br2 and CCl4 is primarily through London dispersion forces (also known as van der Waals forces). These are weak intermolecular forces that occur due to temporary shifts in electron density.

- Examine Solubility of CH3CH2OH and H2O

Assess the solubility of ethanol (CH3CH2OH) in water (H2O). Both ethanol and water are polar molecules. This similarity suggests they are miscible and thus will form a homogeneous solution.

- Determine Forces between CH3CH2OH and H2O

The forces between ethanol (CH3CH2OH) and water (H2O) are hydrogen bonds, which are a type of strong dipole-dipole interaction. This is due to the ability of the hydroxyl (-OH) group in ethanol to form hydrogen bonds with water molecules.

Key concepts

Homogeneous Solutions

A homogeneous solution is a mixture at the molecular level where the components are uniformly distributed, resulting in a single phase system. This is distinct from heterogeneous mixtures, where different phases are visible. A classic example of a homogeneous solution is salt water, where the salt (sodium chloride) is completely dissolved in the water, forming a clear and uniform solution.

In the context of the given exercise, the solubility of various substances in water was examined to determine if they form homogeneous solutions. For instance, while potassium chloride (KCl) dissolves in water to form a homogeneous solution, carbon tetrachloride (CCl4) does not mix well with water due to the difference in polarity between the two substances.

Polar and Nonpolar Substances

The concept of polarity is crucial in understanding solubility and the formation of solutions. Polar substances have a significant difference in electronegativity between their atoms, resulting in a dipole moment. Water, with its bent shape and highly polar O-H bonds, is a prime example of a polar molecule.

Nonpolar substances, on the other hand, do not have a significant difference in electronegativity between bonded atoms, leading to an even distribution of electrical charge. Carbon tetrachloride (CCl4), used in the exercise, is nonpolar because of its symmetrical tetrahedral shape and uniform distribution of charge. These characteristics determine how substances interact with each other and ultimately, whether they form homogeneous solutions.

Ion-Dipole Forces

Ion-dipole forces are a type of intermolecular force that occurs between charged ions and polar molecules. These forces are considerably stronger than other kinds of dipole interactions because of the full charge on ions compared to a partial charge on dipoles. In the context of our solution, the ion-dipole forces between the polar water molecules and the ionic potassium chloride (KCl) allow KCl to dissolve in water, resulting in a homogeneous solution.

During solvation, water molecules surround each ion from KCl. The positive part of the water's dipole aligns with the chloride anion and the negative part with the potassium cation, showcasing the ion-dipole attraction.

London Dispersion Forces

London dispersion forces, also known as instantaneous dipole-induced dipole forces, are a type of van der Waals force. They are the weakest form of intermolecular interaction but crucial for nonpolar substances. These forces emerge from temporary fluctuations in electron density in molecules, resulting in an instantaneous dipole that can induce a dipole in neighboring molecules.

For example, the molecules of bromine (Br2) and carbon tetrachloride (CCl4) from the exercise display London dispersion forces. The nonpolar nature of both substances allows them to mix, forming a homogeneous solution due to these transient induced dipoles.

Hydrogen Bonding

Hydrogen bonding is an exceptionally strong type of dipole-dipole interaction between a hydrogen atom bonded to a highly electronegative atom, such as oxygen or nitrogen, and another electronegative atom bearing a lone pair of electrons. Water's ability to form hydrogen bonds with other polar substances, like ethanol (CH3CH2OH), is critical for creating homogeneous solutions.

In the exercise, the hydroxyl (−OH) group in ethanol can participate in hydrogen bonding with the water molecules, resulting in a stable homogeneous mixture. This strong interaction not only affects solubility but also influences boiling points and the physical properties of substances that can create these bonds.

Miscibility of Liquids

Miscibility refers to the ability of two substances to mix in all proportions, forming a homogeneous solution. It is often discussed in the context of liquids. Two liquids that mix completely, like ethanol (CH3CH2OH) and water (H2O), are said to be miscible. A key factor determining miscibility is the compatibility of intermolecular forces between two substances.

In the given exercise, the miscibility of ethanol in water leads to a uniform solution due to the similar polar nature of both and the strong hydrogen bonds that form between them. Understanding the concept of miscibility is essential in many applications, from pharmacology to chemical engineering.