Question

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 yiew

Short answer

Ethanol creates an area with a lower concentration of water, causing an osmotic gradient. As a result, the water in the ear moves towards and mixes with the ethanol, making it seem like the ethanol is 'drawing out' the water.

Step-by-step solution

Knowing the Variables

Identify the variables in the given situation. Here, there are two mediums involved: water, which is in the ear, and alcohol (ethanol), which is used to draw out the water.

Understanding the Mechanism of Osmosis

Osmosis is the process where a solvent (in this case, water) moves from an area of low solute concentration to an area of high solute concentration across a selectively permeable membrane. This will be the key mechanism through which ethanol draws water out.

Role of Ethanol

Ethanol is a less polar molecule than water, so it is less able to dissolve salts (which are present in the water in our bodies). Therefore, when a drop of ethanol is placed in an ear filled with water, it creates an area of lower concentration of water (because the ethanol doesn't carry the body's salts), creating an osmotic gradient.

Final Explanation

Since water moves towards areas of higher solute concentration to attempt to equalize the concentration, the water in the ear will move towards and mix with the ethanol. As a result, it seems like the ethanol 'draws out' the water from the ear.

Key concepts

Ethanol

Ethanol is a type of alcohol that plays an interesting role in the process of osmosis. In the context of removing water from an ear, ethanol's properties are crucial. Ethanol is less polar compared to water,
which means it doesn't dissolve salts and other solutes as effectively as water does. This characteristic is essential when ethanol is introduced into the water-filled ear.

• Less Attractive to Ions: Because ethanol doesn’t carry ions well, it creates a situation where fewer particles are suspended in it.
• Volatile Nature: Ethanol can evaporate quickly at room temperature, further affecting its behavior when in contact with water.
• Molecular Attraction: Ethanol molecules are attracted to water molecules, creating a focused gradient where water is more drawn towards ethanol than staying within the body solutes.

When a drop of ethanol is applied to an ear blocked with water, it initiates movement and mixing of the water molecules due to these properties.

Solute Concentration

Solute concentration refers to how much solute is present within a solution. Higher solute concentration in one area compared to another creates an osmotic gradient.
This is vital in understanding how ethanol draws out water from the ear. The ear filled with water has a certain amount of body salts dissolved in it, making it slightly higher in solute concentration.

• High vs. Low Concentration: A critical part of osmosis, water naturally moves towards areas of higher solute concentrations. When ethanol (low solute concentration) meets water in the ear (higher solute concentration), it causes an osmosis-induced movement.
• Balancing Act: The goal of osmosis is to equalize solute concentrations, leading water to shift towards the ethanol side, where salt concentration is minimal.
• Resulting Action: As solutes attempt to balance, more water gets mixed and diffused into the ethanol, as observed by the water being 'drawn out.'

Molecular Mechanism

The molecular mechanism at play when ethanol draws out water involves the process of osmosis. Osmosis is all about the movement of water from areas of low solute concentration to high solute concentration
through a selectively permeable membrane. This natural movement is driven by the need to achieve balance within a solution.

• Movement Dynamics: Water molecules from the ear have relatively less solute concentration in the ethanol and thus migrate towards it through this gradient.
• Permeability Factors: None of this would occur without the ear acting as a semi-permeable medium, allowing this directional flow.
• Energy Independence: Osmostic movement does not require energy, as it leverages the natural tendency of molecules to strive for equilibrium.

In summary, the subtle yet powerful mechanism of osmosis ensures that water shifts from a saline ear environment to the lower solute concentration provided by ethanol, making it seem as though the water is being actively 'drawn out.'