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Chapter 11: Problem 139

Swimming coaches sometimes suggest that a drop of alcohol (ethanol) placed in an ear plugged with water "draws out the water." Explain this action from a molecular point of view.

Short Answer

Expert verified
Ethanol, due to its polar nature, mixes easily with water due to hydrogen bonding, and due to its dual solubility in both water and oil, it can penetrate the ear, mixing with both wax and water. When it subsequently evaporates, it removes some water with it.

Step by step solution

01

Understanding the Initial Scenario

Before attempting to explain the process, it would be useful to first understand the substances involved. We are dealing with water, ethanol, and potentially, the ear itself. Both ethanol and water are polar molecules, meaning they have a net dipole as a result of the opposing charges (i.e. having partial positive and partial negative charges) from polar bonds arranged asymmetrically. Ethanol and water are miscible in all proportions, which indicates ethanol can dissolve in water in all proportions.
02

Role of Polarity and Hydrogen Bonding

The solubility of ethanol in water is primarily due to hydrogen bonding. Ethanol has a hydroxyl (\(OH\)) group that can form a hydrogen bond with water molecules. Hydrogen bonds are among the strongest intermolecular forces. When a drop of ethanol is added to the water-clogged ear, the ethanol disruptively interacts with the water's hydrogen bonding network. This is also enhanced by ethanol's smaller molecular size, which allows it to get between water molecules more readily.
03

Describing the 'Drawing Out' Process

Because of its dual solubility in both water and oil-based substances (due to its nonpolar hydrocarbon chain and polar hydroxyl group), ethanol can penetrate deep into the ear and disrupt both the water and the wax in the ear. When the ethanol eventually evaporates, it takes with it some of the water it has mixed with, hence 'drawing out the water'. It's also worth noting that the quick evaporation of lower alcohols like ethanol causes a cooling effect, and the ear feels cooler.

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