Question

Which of the following pairs of substances would you expect to form solutions? (a) \(\mathrm{CCl}_{4}\) and water (b) Benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) and \(\mathrm{MgSO}_{4}\) (c) Hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\) and heptane \(\left(\mathrm{C}_{7} \mathrm{H}_{16}\right)\) (d) Ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) and heptanol \(\left(\mathrm{C}_{7} \mathrm{H}_{15} \mathrm{OH}\right)\)

Short answer

Pairs (c) and (d) will form solutions.

Step-by-step solution

Understand Polar vs Nonpolar

To determine if substances will form solutions, consider the principle "like dissolves like." Polar substances dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents.

Analyze Pair (a) - CCl4 and Water

Carbon tetrachloride (\(\mathrm{CCl}_{4}\)) is nonpolar, while water is polar. Since they don't share similar polarities, they won't form a solution.

Analyze Pair (b) - Benzene and MgSO4

Benzene (\(\mathrm{C}_{6} \mathrm{H}_{6}\)) is nonpolar, while \(\mathrm{MgSO}_{4}\) is an ionic compound and generally polar due to its ions. These will not form a solution.

Analyze Pair (c) - Hexane and Heptane

Both hexane (\(\mathrm{C}_{6} \mathrm{H}_{14}\)) and heptane (\(\mathrm{C}_{7} \mathrm{H}_{16}\)) are nonpolar hydrocarbons. Since they are similar in polarity, they will form a solution.

Analyze Pair (d) - Ethanol and Heptanol

Both ethanol (\(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)) and heptanol (\(\mathrm{C}_{7} \mathrm{H}_{15} \mathrm{OH}\)) are alcohols and polar, due to their hydroxyl groups. They will form a solution.

Key concepts

Polar and Nonpolar Substances

When it comes to solutions, understanding the nature of "polar" and "nonpolar" substances is crucial. Polar substances have a distinct separation of electric charge. This results in positive and negative poles. Water, for example, is a classic polar substance. This is because it has a bent shape and a significant difference in electronegativity between hydrogen and oxygen. On the other hand, nonpolar substances have molecules with balanced electron distributions. Therefore, they have no distinct poles of charge. Examples of nonpolar substances include oils and hydrocarbons like d

How Polar and Nonpolar Substances Interact

Polar substances tend to interact well with one another, primarily due to the attraction between opposite charges. This explains why salt and water mix so readily. Nonpolar substances, however, do not have these poles. As a result, they prefer to interact with each other, avoiding interactions with polar substances. Understanding these differences is key when predicting whether two substances will form a solution.

Like Dissolves Like Principle

The "like dissolves like" principle is a helpful rule of thumb in chemistry to predict solubility. Simply put, this rule states that substances with similar polarities will dissolve in each other. This principle is based on the interactions between molecules.

• **Polar solvents** will dissolve **polar solutes**. An example is sugar (polar) dissolving in water (polar).
• **Nonpolar solvents** will dissolve **nonpolar solutes**. Think of wax (nonpolar) dissolving in turpentine (nonpolar).

There are exceptions, of course, but this general guideline helps discern why certain substances form solutions, while others do not. If two substances do not dissolve in each other, their molecular interactions are likely incompatible, i.e., one is polar and the other is nonpolar.

Ionic Compounds

Ionic compounds are a category of substances formed from the electrostatic attraction between oppositely charged ions. Table salt (\( \text{NaCl} \) ) is an iconic example, consisting of positively charged sodium ions and negatively charged chloride ions.

Solubility of Ionic Compounds

In solution chemistry, they are generally considered polar due to the presence of charged particles. Because of their polarity, ionic compounds dissolve well in polar solvents like water. When ionic compounds dissolve, their ions separate and disperse throughout the solvent. But ionic compounds do not mix with nonpolar solvents due to the lack of charge attraction. Understanding the nature of ionic compounds and their interactions is fundamental in predicting solubility outcomes in various chemical processes.