Question

Why does water not dissolve motor oil?

   Why does water not dissolve motor oil?

Fundamentals of General, Organic, and Biological Chemistry

Fundamentals of General, Organic, and Biological Chemistry

John McMurry, David… 1st Edition

Chapter 9, Problem 35

Instant Answer

Solved by Expert Shahina -

01/07/2022

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"Like dissolves like": polar solvents dissolve polar solutes, nonpolar solvents dissolve nonpolar solutes. Show more…

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Why does water not dissolve motor oil?

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Key Concepts

Like Dissolves Like

The principle of 'like dissolves like' states that polar solvents tend to dissolve polar substances, and nonpolar solvents are more effective at dissolving nonpolar substances. Since water is a polar solvent and motor oil is nonpolar, the chemical incompatibility prevents them from mixing, leading to immiscibility.

Intermolecular Forces

Intermolecular forces such as hydrogen bonding in water facilitate strong attractions between polar molecules. Motor oil, being composed mainly of hydrocarbons, relies on weaker Van der Waals forces. The mismatch in these forces means that the thermodynamic interactions necessary for dissolution do not occur between water and motor oil.

Molecular Polarity

Molecular polarity refers to the distribution of electrical charge over the atoms in a molecule. Water molecules are polar, meaning they have a significant difference in electronegativity between the oxygen and hydrogen atoms, which creates a dipole moment. In contrast, the components of motor oil are nonpolar, lacking a significant charge separation, which is key to understanding why they do not mix well.

Hydrophobicity

Hydrophobicity is the tendency of nonpolar substances to repel water. Motor oil is hydrophobic, meaning it avoids interaction with water molecules. This property further explains why water does not effectively dissolve motor oil, as hydrophobic substances tend to aggregate away from polar solvents like water.

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