Oil and water are immiscible. Which is the most likely reason? (a) Oil molecules are denser than water. (b) Oil molecules are composed mostly of carbon and hydrogen. (c) Oil molecules have higher molar masses than water. (d) Oil molecules have higher vapor pressures than water. (e) Oil molecules have higher boiling points than water.

Verified step by step guidance

1. Understand the concept of immiscibility: Immiscibility refers to the inability of two substances to mix and form a homogeneous solution. In the case of oil and water, they do not mix because of differences in their molecular properties.
2. Consider the polarity of molecules: Water is a polar molecule, meaning it has a partial positive charge on one side and a partial negative charge on the other. Oil, on the other hand, is nonpolar, primarily composed of carbon and hydrogen atoms, which do not have significant charge separation.
3. Apply the 'like dissolves like' principle: This principle states that polar substances tend to dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents. Since oil is nonpolar and water is polar, they do not mix well.
4. Evaluate the options: (a) Density, (c) molar mass, (d) vapor pressure, and (e) boiling point are not directly related to the immiscibility of oil and water. The key factor is the molecular composition and polarity, which is addressed in option (b).
5. Conclude that the most likely reason for the immiscibility of oil and water is option (b): Oil molecules are composed mostly of carbon and hydrogen, making them nonpolar and unable to mix with polar water molecules.

Key Concepts

Polarity

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Water is a polar molecule, meaning it has a partial positive charge on one side and a partial negative charge on the other, allowing it to form hydrogen bonds. In contrast, oil molecules are nonpolar, lacking significant charge separation, which prevents them from interacting favorably with water molecules, leading to immiscibility.

Hydrophobic and Hydrophilic Interactions

Hydrophobic interactions occur between nonpolar substances, like oil, which do not mix well with polar substances, such as water. Hydrophilic substances, on the other hand, are attracted to water. The inability of oil to form hydrogen bonds with water molecules results in the separation of the two liquids, as oil molecules prefer to associate with each other rather than with water.

Density and Miscibility

Density is a measure of mass per unit volume and can influence the behavior of liquids. While oil is generally less dense than water, which causes it to float, the primary reason for their immiscibility is not density but rather the differences in polarity. Miscibility is determined by the ability of substances to mix at a molecular level, which is hindered in this case due to the nonpolar nature of oil.