Question

What do we mean when we say that "like dissolves like"? Do two molecules have to be identical to be able to form a solution in one another?

Short answer

"Like dissolves like" means that substances with similar polarities (either polar or nonpolar) will dissolve each other due to their similar intermolecular forces. It does not imply that the molecules need to be identical; instead, they must have similar polarity characteristics to form a solution. Polar molecules, such as water, can dissolve other polar substances, while nonpolar molecules, like oil, can dissolve nonpolar substances.

Step-by-step solution

Understanding Polar and Nonpolar Molecules

First, let's define what polar and nonpolar molecules are. Molecules can be classified according to their polarity, which is the distribution of charges within the molecule. - Polar molecules: these have a separation of charges, meaning that one part of the molecule is more negatively charged while the other part is more positively charged. This happens because of differences in electronegativity between the atoms involved in a chemical bond. For example, water (H_2O) is a polar molecule because its oxygen atom is more electronegative than its hydrogen atoms, creating a dipole moment. - Nonpolar molecules: these have a uniform distribution of charges, meaning that there is no separation of charges within the molecule. This is observed in molecules where the atoms share electrons more evenly and have similar electronegativity values. An example of a nonpolar molecule is methane (CH_4).

Understanding "Like Dissolves Like"

"Like dissolves like" is a principle used to predict or explain the solubility of substances. This principle states that polar substances will tend to dissolve other polar substances, while nonpolar substances will tend to dissolve nonpolar substances. This solubility pattern occurs because molecules with similar polarities have similar intermolecular forces, allowing them to interact and ultimately dissolve each other. For instance, water (a polar molecule) can dissolve sugar (also a polar molecule), but water is not effective at dissolving oil (a nonpolar substance). Similarly, oil (nonpolar) is able to dissolve other nonpolar substances like fat, but it cannot dissolve polar substances like salt.

Identical Molecules Not Required for Solvation

Now we understand that "like dissolves like" simply means that substances with similar polarities can dissolve each other. However, this does not imply that the two molecules must be identical. As long as the substances have similar polarity characteristics (either both polar or both nonpolar), they can potentially form a solution, as their intermolecular forces will allow for dissolution to occur. In conclusion, the term "like dissolves like" refers to the concept that similar polarities among molecules result in their ability to dissolve each other, regardless of whether the molecules are identical or not. It is the alignment of polar or nonpolar properties that allow for the formation of solutions between various substances.