One of two glass capillary tubes of the same diameter is...

One of two glass capillary tubes of the same diameter is placed in a dish of water and the other in a dish of ethanol $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right) .$ Which liquid will rise higher in its tube? Explain your answer.

Key Concepts

Capillary Action

Capillary action is the phenomenon where a liquid either rises or falls in a narrow tube due to the interplay between adhesive forces (between the liquid and the solid surface) and cohesive forces (within the liquid molecules). It is fundamentally important when studying liquids in confined spaces and is governed by factors such as surface tension, contact angle, and the tube’s diameter.

Surface Tension

Surface tension is the result of cohesive forces among liquid molecules, which create a 'stretched' surface layer behaving like an elastic sheet. In the context of capillary action, a liquid with higher surface tension, like water, will typically rise higher in a capillary tube because the stronger intermolecular forces promote a higher upward pull along the tube walls.

Contact Angle

The contact angle measures the degree of wetting of a solid by a liquid. It is defined as the angle formed between the tangent to the liquid surface and the solid surface at the point of contact. A smaller contact angle implies stronger adhesion of the liquid to the tube, enhancing capillary rise, while a larger contact angle weakens this adhesive effect.

Liquid Density

Liquid density plays a role in capillary action as it appears in the denominator of the capillary rise equation. A lower density liquid would generally rise higher in a capillary tube, assuming other factors like surface tension and contact angle remain constant, because less weight is exerted downward by the lifted liquid column.

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