Question

(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

(a) Adhesive forces are the forces between different types of molecules, while cohesive forces are the forces between like molecules. (b) When a paper towel absorbs water, adhesive forces cause water molecules to stick to the paper towel fibers, and cohesive forces hold the water molecules together. (c) The U-shaped meniscus in a glass tube is formed due to the stronger adhesive forces between water molecules and glass surface compared to the cohesive forces within the water molecules, causing the water to climb up the sides of the tube.

Step-by-step solution

Define Adhesive Forces

Adhesive forces are the forces that hold different types of molecules together. These forces occur between different types of molecules that come into close contact with one another. Some examples of adhesive forces include water droplets sticking to a glass surface, or glue bonding two different materials together.

Define Cohesive Forces

Cohesive forces are the forces that hold like molecules together, meaning they occur within the same type of material. Some examples of cohesive forces include water molecules sticking together or the forces holding together a solid piece of metal.

Identify Adhesive and Cohesive Forces Involved When a Paper Towel Absorbs Water

When a paper towel absorbs water, both adhesive and cohesive forces come into play. The adhesive forces are responsible for the water molecules sticking to the fibers of the paper towel, while the cohesive forces are the forces holding the water molecules together. The strength of the adhesive forces between the water and the paper towel fibers is greater than the cohesive forces within the water molecules, which allows the water to be absorbed by and spread throughout the paper towel.

Explain the Cause for the U-shaped Meniscus Formed When Water is in a Glass Tube

When water is placed in a glass tube, a U-shaped meniscus forms. This occurs due to the interaction between adhesive and cohesive forces. The adhesive forces between the water molecules and the glass surface are stronger than the cohesive forces within the water molecules, causing the water to stick to the glass and climb up the sides of the tube. This movement creates the U-shaped curve called the meniscus.