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Chapter 11: Problem 34

(a) Distinguish between adhesive forces and cohesive forces. (b) What adhesive and cohesive forces are involved when a paper towel absorbs water? (c) Explain the cause for the U-shaped meniscus formed when water is in a glass tube.

Short Answer

Expert verified
Adhesive forces are the attractive forces between molecules of different substances, while cohesive forces are the attractive forces between molecules of the same substance. In the case of a paper towel absorbing water, the adhesive forces are between the water molecules and the paper towel fibers, and the cohesive forces are between the water molecules themselves. The U-shaped meniscus formed when water is in a glass tube is due to the balance between these adhesive and cohesive forces, with the adhesive forces between the water molecules and the glass being stronger than the cohesive forces between the water molecules.

Step by step solution

01

Definition of Adhesive Forces

Adhesive forces are the forces of attraction between molecules from two different substances. These forces cause two different materials to stick together.
02

Definition of Cohesive Forces

Cohesive forces are the forces of attraction between molecules of the same substance. These forces hold the molecules together within a single material.
03

Forces Involved in the Absorption of Water by a Paper Towel

When a paper towel absorbs water, both adhesive and cohesive forces are involved. The adhesive forces are between the water molecules and the paper towel fibers, which cause the water to be attracted to and stick to the paper towel. The cohesive forces are between the water molecules themselves, which hold the water together as it is absorbed by the paper towel.
04

Cause of the U-Shaped Meniscus When Water is in a Glass Tube

When water is in a glass tube, a U-shaped meniscus forms due to the interplay between adhesive and cohesive forces. Adhesive forces between the water molecules and the glass cause the water to be attracted to the glass, resulting in the water climbing up the sides of the tube. The cohesive forces between the water molecules, on the other hand, pull the water together, maintaining its curved shape within the tube. This balance between adhesive and cohesive forces creates the U-shaped meniscus. In this case, the adhesive forces between the water molecules and the glass are stronger than the cohesive forces between the water molecules themselves.

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Most popular questions from this chapter

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