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Chapter 7: Problem 979

Soap helps in cleaning because (A) chemicals of soap change (B) It increase the surface tension of the solution. (C) It absorbs the dirt. (D) It lowers the surface tension of the solution

Short Answer

Expert verified
Soap helps in cleaning by lowering the surface tension of the solution, allowing water molecules to spread out and penetrate dirt and grease more easily. This is due to soap being a surfactant, with molecules composed of a hydrophilic head and hydrophobic tail that form micelles to trap and wash away dirt. Therefore, the correct answer is (D) It lowers the surface tension of the solution.

Step by step solution

01

Define surface tension

Surface tension is a property of liquids that results from the cohesive forces between its molecules. It is defined as the force per unit length acting perpendicular to an imaginary line drawn on a liquid's surface. This causes the liquid to behave like a stretched elastic membrane.
02

Discuss the properties of soap

Soap is a surfactant, meaning it reduces the surface tension of liquid solutions. Soap molecules are composed of a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. When dissolved in water, they arrange themselves in such a way that the hydrophilic heads face towards the water, while the hydrophobic tails face away from the water, forming micelles.
03

Explain the role of soap in cleaning

As a surfactant, soap lowers the surface tension of the water, making it easier for the water molecules to spread out and penetrate the surfaces of dirt and grease. These particles then get surrounded by the soap molecules, with the hydrophobic tails facing towards the dirt and the hydrophilic heads facing away. This structure, called a micelle, traps the dirt and allows it to be washed away along with the soap and water.
04

Choose the correct answer

Based on our discussion, soap helps in cleaning by lowering the surface tension of the solution. So, the correct answer is: (D) It lowers the surface tension of the solution.

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