Question

Solutes that easily dissolve in water are said to be a. hydrophobic. b. hydrophilic. c. polar molecules. d. all of the above. e. \(b\) and \(c\) only.

Short answer

The correct answer is e. hydrophilic and polar molecules (b and c only). These types of substances dissolve in water while hydrophobic substances do not.

Step-by-step solution

Identify Definitions

Understand that hydrophobic substances repel or do not mix with water, while hydrophilic substances easily mix with or dissolve in water. Polar molecules, owing to their polarity, can also dissolve in water which itself is a polar molecule.

Eliminate Wrong Answers

Based on these definitions, answer choice a. hydrophobic can be eliminated as they repel water, not dissolve in it. We are left with b. hydrophilic, c. polar molecules, d. all off the above, or e. b and c only

Select the Correct Answer

Given that both hydrophilic substances and polar molecules dissolve in water, the correct answer is e. b and c only.

Key concepts

Polar molecules

Polar molecules have a unique feature: they have a positive end and a negative end. This happens because of the uneven distribution of electrons within the molecule. Water itself is a great example of a polar molecule. Its molecules are shaped in such a way that there is a partial positive charge on one side and a partial negative charge on the other.
As a result, polar molecules are attracted to water molecules. They can interact readily, which is why polar substances often dissolve well in water. This quality is due to the attraction between the opposite charges (positive and negative) that help pull the polar solutes into solution.

Hydrophobic substances

Hydrophobic is a fancy word for 'water-fearing'. These substances tend to repel water or avoid mixing with it. This is mainly because hydrophobic substances are non-polar. They do not have charged ends like polar molecules do, and so they do not have a natural attraction to water molecules.
Consider oils as an example. When you try to mix oil with water, the oil droplets cluster together rather than dissolve, forming a separate layer. This behavior is a classic trait of hydrophobic substances. Understanding this property helps explain why certain materials don't mix with water at all.

Solubility in water

Solubility refers to the ability of a substance to dissolve in a solvent, in this case, water. Solubility depends on the nature of both the solute (the substance dissolving) and the solvent (the liquid).

• Hydrophilic Solutes: These substances are water-loving and readily dissolve in water. They are often polar, which allows them to interact well with the polar water molecules.
• Polar Molecules: Due to their polarity, these also dissolve effectively in water. Water, being polar, has a partial positive charge near the hydrogen atoms and a partial negative charge near the oxygen atom, which attracts polar solutes.

This is why both hydrophilic and polar substances often dissolve easily in water, enhancing their solubility.