Skip to main content
Pearson+ LogoPearson+ Logo
Ch.13 - Properties of Solutions
All textbooksBrown 14th EditionCh.13 - Properties of SolutionsProblem 28
Chapter 13, Problem 28

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.
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.
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.
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).
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.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
1m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.
Recommended video:
Guided course
02:38
Molecular Polarity

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.
Recommended video:
Guided course
03:01
The greatest ligand-orbital interactions result in the greatest increase in energy.

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.
Recommended video:
Guided course
01:56
Density Concepts
Related Practice
Textbook Question

By referring to Figure 13.15, determine the mass of each of the following salts required to form a saturated solution in 250 g of water at 30 °C: (b) Pb(NO3)2,

Textbook Question

By referring to Figure 13.15, determine the mass of each of the following salts required to form a saturated solution in 250 g of water at 30 °C: (c) Ce2(SO4)3.

Textbook Question

Which of the following in each pair is likely to be more soluble in hexane, C6H14: (a) CCl4 or CaCl2, (b) benzene (C6H6) or glycerol, CH2(OH)CH(OH)CH2OH, (c) octanoic acid, CH3CH2CH2CH2CH2CH2CH2COOH, or acetic acid, CH3COOH? Explain your answer in each case.

1
views
Textbook Question

Which of the following in each pair is likely to be more soluble in water: (a) cyclohexane (C6H12) or glucose (C6H12O6),