Problem 45 - Chemistry A Molecular Approach

Question

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. MISSED THIS? 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 \(\mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

a. No homogeneous solution; b. Homogeneous solution, ion-dipole forces; c. Homogeneous solution, London dispersion forces; d. Homogeneous solution, hydrogen bonding.

Step 1 - Analyzing Solubility of CCl4 and H2O

Carbon tetrachloride ((CCl_{4})) is a nonpolar solvent, while water ((H_{2}O)) is a polar solvent. According to the 'like dissolves like' principle, nonpolar solvents usually do not mix well with polar solvents to form a homogeneous solution.

Step 2 - Analyzing Solubility of KCl and H2O

Potassium chloride ((KCl)) is an ionic compound and water ((H_{2}O)) is polar; ionic compounds tend to dissolve well in polar solvents due to the strong ion-dipole forces between the ions and the polar water molecules, resulting in a homogeneous solution.

Step 3 - Analyzing Solubility of Br2 and CCl4

Bromine ((Br_{2})) is a nonpolar molecule, and carbon tetrachloride ((CCl_{4})) is a nonpolar solvent. Nonpolar molecules generally dissolve well in nonpolar solvents, so a homogeneous solution is expected to form.

Step 4 - Analyzing Solubility of CH3CH2OH and H2O

Ethanol ((CH_{3}CH_{2}OH)) and water ((H_{2}O)) are both polar and can hydrogen bond with each other, so they mix readily to form a homogeneous solution. Hydrogen bonding is the dominant force involved here.

Key Concepts

Like Dissolves Like Principle

The concept of 'like dissolves like' is a fundamental principle in chemistry that plays a vital role in the formation of solutions. It states that substances with similar chemical properties tend to be more soluble in each other.

In terms of polarity, polar solvents, such as water (H₂O), are more likely to dissolve polar substances or ionic compounds, which have charges due to uneven electron distribution. This is because of the attraction between the oppositely charged parts of the molecules. Conversely, nonpolar solvents, like carbon tetrachloride (CCl₄), can dissolve nonpolar substances because there is no significant charge separation in the molecules, and they can evenly distribute electron density.

The principle is easy to observe in everyday life—think about how oil (nonpolar) and water (polar) separate, while sugar (polar) dissolves well in water. Understanding this principle assists in predicting whether a substance will form a homogeneous solution with another based on their polarities.

Polar and Nonpolar Solvents

Solvents can be classified as either polar or nonpolar, and this distinction is crucial for understanding solubility.

Polar Solvents

These solvents have a significant charge difference across their molecules, creating a dipole. Water (H₂O) is one of the most common polar solvents and is excellent at dissolving many salts like potassium chloride (KCl), due to its ability to create strong ion-dipole interactions.

Nonpolar Solvents

Nonpolar solvents, such as carbon tetrachloride (CCl₄), lack this significant charge difference. They are better at dissolving nonpolar substances like bromine (Br₂) because there is no preference for charge in their molecular structure.

Knowing the nature of the solvent helps in explaining and predicting solubility. For instance, iodine (a nonpolar molecule) will dissolve in nonpolar solvents like hexane but not in polar solvents such as water.

Homogeneous Solutions

A homogeneous solution is one where the solute is evenly distributed throughout the solvent, creating a single phase with uniform composition. This can happen with both solids in liquids, like salt in water, or liquids in liquids, like alcohol in water.

Homogeneity is influenced by the nature of the solvent and solute interaction. For example, ethanol (CH₃CH₂OH) can form hydrogen bonds with water molecules, resulting in a mixture where the ethanol is completely dispersed within the water, making it a homogeneous solution.

Creating these types of solutions requires considering both the 'like dissolves like' principle and the solvent's ability to overcome the solute's existing intermolecular forces. Homogeneous solutions are widely used in various industries, including pharmaceuticals, food production, and chemical manufacturing.