Question

Determine whether a homogeneous solution forms when each pair of substances is mixed. (a) \(\mathrm{CCl}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2} \mathrm{O}\)

Short answer

\(\mathrm{CCl}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\) will not form a homogeneous solution, whereas \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\), and \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2}\mathrm{O}\) will form homogeneous solutions.

Step-by-step solution

Understand Solubility Principles

Solubility is largely guided by the 'like dissolves like' principle, which states that polar substances are soluble in polar solvents, and nonpolar substances are soluble in nonpolar solvents.

Analyze the Polarity of \(\mathrm{CCl}_{4}\) and \(\mathrm{H}_{2} \mathrm{O}\)

\(\mathrm{CCl}_{4}\) is a nonpolar molecule due to its symmetric tetrahedral structure and identical (nonpolar) C-Cl bonds, while \(\mathrm{H}_{2} \mathrm{O}\) is a polar molecule. Therefore, they are not likely to form a homogenous solution.

Analyze the Polarity of \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\)

Both \(\mathrm{Br}_{2}\) and \(\mathrm{CCl}_{4}\) are nonpolar molecules. They will form a homogeneous solution since a nonpolar solute will dissolve in a nonpolar solvent.

Analyze the Polarity of \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{H}_{2}\mathrm{O}\)

Both \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethyl alcohol) and \(\mathrm{H}_{2}\mathrm{O}\) are polar due to their hydroxyl (-OH) groups. Therefore, they will form a homogeneous solution since a polar solute will dissolve in a polar solvent.

Key concepts

Like Dissolves Like

When it comes to understanding why certain substances mix well together while others don’t, the rule of thumb is 'like dissolves like'. This principle implies that substances with similar properties, particularly in terms of polarity, are more likely to dissolve in each other and form solutions.

For example, polar substances, which have a noticeable distribution of charge, tend to dissolve well in polar solvents - liquids with a similar uneven charge distribution. Conversely, nonpolar substances lacking a significant charge difference dissolve in nonpolar solvents because there is no attraction to the poles of a polar solvent.

This principle is extremely useful for predicting the solubility of a compound in a particular solvent without having to actually mix the substances together.

Polarity of Molecules

The concept of polarity is instrumental in determining solubility. The polarity of a molecule arises from the distribution of electrons across its structure and is greatly influenced by the presence of polar bonds and the geometry of the molecule.

A polar molecule possesses a positive pole and a negative pole, due to more electronegative atoms drawing electrons towards themselves, resulting in areas of partial positive and negative charges. Nonpolar molecules do not have significant partial charges, often due to a symmetrical arrangement of atoms that allows for even distribution of electron density. Understanding the polarity of molecules enables us to apply the 'like dissolves like' principle with greater precision.

Homogeneous Solutions

A homogeneous solution is a mixture in which the composition is uniform throughout. This type of solution is the result of a solute that completely dissolves in the solvent, leaving no visible boundaries or separate phases.

The creation of a homogeneous solution depends on the interaction between the solute and solvent at the molecular level. The intermolecular forces between both substances need to be of similar strength and type for a solution to be homogeneous. If these forces are comparable, the solute will disperse uniformly throughout the solvent, resulting in what you see as a clear and consistent mixture.

Chemical Solubility

Chemical solubility refers to the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature and pressure. Solubility is not only govern by polarity but also by other factors such as temperature, and pressure, as well as the nature of the solute and solvent.

When a solute dissolves, it interacts with the solvent to form what's known as a 'solvated' state. This means that the solute's particles are surrounded by solvent molecules. If the solute and solvent have compatible intermolecular forces, solvation takes place readily, and we observe a higher degree of solubility. In cases where the solute's intermolecular forces are much stronger than the interaction with the solvent, solubility is low, and you may see undissolved substance remaining, indicating saturation or limited solubility.