Check sibling questions

Soaps and detergents are two types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.

 

Answer

  • Difference between Soaps and Detergents:

 

Soaps

Detergents

 
  • They are sodium or potassium salts of long chain fatty acids or carboxylic acids.
  • They are ammonium or sulphonate salts of long chain carboxylic acid.
 
  • They work only with soft water.
  • They work with both hard and soft water.
 
  • They are fully biodegradable.
  • They are non-biodegradable.

 

 

  • Cleansing action of soap:

Soap molecules are arranged in a specific manner which is known as micelles . In this arrangement, the polar head being hydrophilic faces outwards and interacts with water and the nonpolar tail being hydrophobic remains inwards and interacts with oil and dirt.

When soap is added to dirty clothes, the hydrophobic part attaches with oil and dirt while the hydrophilic part remains in contact with water molecules . Because of this arrangement of the soap molecules, it is able to remove dirt from the surfaces and we can wash the clothes clean.

Structure of micelle:

Structure of Hydrophilic group - Teachoo.png

  • Soap does not form lather with hard water because the calcium and magnesium ions present react with soap to form white sticky scum.
  • The problems that arise due to excessive use of detergents are:
  1. Detergents are non-biodegradable so they accumulate in the environment and cause pollution.
  2. The entry of detergents in the ecosystem may lead to bioaccumulation in living beings.
  3. They may also alter the pH of the soil.  

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo