What does “like dissolves” mean? In other words, why can’t polar substances such as oil dissolve in water?
The correct answer and explanation is:
The phrase “like dissolves like” refers to the principle that substances with similar types of intermolecular forces tend to dissolve in each other. In simpler terms, polar substances dissolve well in other polar substances, and nonpolar substances dissolve in other nonpolar substances. This happens because the forces between molecules of the same type are compatible, allowing them to interact effectively and form a solution.
Water is a highly polar solvent, meaning it has molecules with distinct positive and negative charges. The oxygen atom in water carries a partial negative charge, while the hydrogen atoms have a partial positive charge. This creates a strong dipole in each water molecule, leading to hydrogen bonding between water molecules.
Oil, on the other hand, is mostly composed of nonpolar molecules. Nonpolar substances do not have a significant positive or negative charge distribution. Instead, the electrons in nonpolar molecules are distributed more evenly. Because of this, oil molecules are held together by weaker forces, known as van der Waals forces, which are much weaker than the hydrogen bonds in water.
When you try to mix oil and water, the strong hydrogen bonds between water molecules cannot interact effectively with the weak van der Waals forces between the oil molecules. This causes the water molecules to prefer staying together, while the oil molecules prefer staying together. As a result, oil and water do not mix, and the two substances form separate layers.
The principle of “like dissolves like” explains why polar substances, like water, are good at dissolving other polar substances (such as salt or sugar) because they can form strong interactions, while nonpolar substances like oil do not mix with polar substances due to their inability to form compatible intermolecular interactions.