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Difference Between Soaps and Detergents

  • Last Updated : 21 Sep, 2021

Soaps and detergents are cleaning agents that aid in the removal of dirt, bacteria, and other undesirable particles from the human body and other surfaces. People frequently misunderstand these two cleansers and use them interchangeably since they are both used for cleaning. However, there are major differences between soaps and detergents in reality. In this article, we shall discuss another cleaning agent known as detergents that overcome most of the limitations of the soaps. Before we discuss what detergents are and study them in detail, let us recall what soaps are.

Soaps

Soap is made by combining sodium hydroxide or potassium hydroxide with vegetable oil or animal fats in a saponification reaction. Soaps are potassium or sodium salts of fatty acids with a lengthy chain. Soaps are naturally water-soluble. 

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A soap molecule is made up of two components. These two components are referred to as:

  1. Hydrophobic tail: This part of the soap is water repellent in nature and dissolves in oils. It is ionic in nature.
  2. Hydrophilic head: This part of the soap molecule is water attractive or water-loving and dissolves in water. It is made up of a long chain of hydrocarbons.

Detergents

Detergents are those compounds that have charged or ionic groups connected to the end of a lengthy hydrocarbon chain. Detergents are long-chain carboxylic acid quaternary ammonium or sulfonate salts. 

Detergents, often known as surfactants, are substances that lower water’s surface tension. Detergents were developed during World War 2 due to the lack of vegetable oils to make soaps. Detergents also contain two parts. These are:

  1. Hydrophobic tail: This part of the detergent is water repellent similar to the soaps. It is the ionic or polar or charged group that is present at the end of the hydrocarbon chain.
  2. Hydrophilic head: This part is water attractive or water-loving. It is made up of a long alkyl hydrocarbon chain.

Properties of Detergents are:

  • Detergents reduce the surface tension of water and are called surfactants.
  • Detergents are soluble in water like soaps. Detergents are even soluble in hard water and do not form scum so they overcome the major limitation of soap.
  • This is because the ionic group present in detergents does not interact with the Mg or Ca ions present in hard water.

Types of Detergents

Detergents are further classified into 3 types depending upon the polarity of the polar group or hydrocarbon chain. These are:

  • Cationic Detergents: Those detergents where the polar group is a cation i.e. positively charged are called cationic detergents. Cationic detergents are generally ammonium salts of chlorides, bromides or acetates. The Nitrogen atom in the polar group of these detergents is positively charged. The positively charged group of the detergent is involved in the cleansing action. An example of cationic detergents is Cetyltrimethylammonium bromide whose structure is shown below.

Cetyltrimethylammonium bromide

This detergent is mainly used in hair conditioners. Cationic detergents are very expensive as they possess antibacterial or germicidal properties. Thus they are of very limited use.

  • Anionic Detergents: Those detergents where the hydrocarbon chain of detergent is an anion i.e. negatively charged are called anionic detergents. The negatively charged group is involved in cleansing in these detergents. Anionic detergents are sodium salts of the sulphurated long chains of alcohols or hydrocarbons. Example: Sodium lauryl sulphate is an anionic detergent and is very commonly used in household items like toothpaste, shampoos, etc.

Sodium lauryl sulphate

  • Non-ionic detergents: They have no ionic part and thus no charge on the cleansing part. They are esters of alcohols of high molecular mass. Liquid dish wash contains non-ionic detergents. An example of non-ionic detergent is Pentaerythrityl stearate.

Pentaerythrityl stearate

The cleansing action of detergents also takes place through micelle formation as discussed in the case of soaps. All the steps are the same as discussed in the other article.



Advantages of Detergents are:

  • Detergents are even soluble in hard water and do not form scum so they can even clean the dirt in hard water.
  • Detergents can be used in salty and acidic water too.
  • Detergents can be used for washing woollens and are not affected by the acidic dyes in them.
  • Detergents are more soluble in water than many soaps.
  • Detergents that have linear hydrocarbon chains are biodegradable in nature and do not cause pollution.

Disadvantages of Detergents are:

  • Detergents are expensive as compared to soaps.
  • As the detergents get more and more branched, they become less biodegradable and cause pollution.
  • Rinsing the detergent requires more water.
  • Excessive alkalis added to the detergents may damage the fabric.

Difference between Detergents and Soaps

The difference between soap and detergent is that soap is a fatty acid and detergent is a combination of surfactants. We use them to clean the house. To distinguish between soap and detergent, we must analyse their characteristics as:

 

Soaps

Detergents

1.Soaps are sodium or potassium salts of a long chain of carboxylic acids.Detergents are ammonium or sulfonate salts of long chains of carboxylic acids.
2.Soaps are mostly biodegradable.Detergents are non-biodegradable.
3.Soaps do not clean well in hard, acidic and saline water.They are effective in hard, saline and acidic water as well.
4.They form scum with hard water.They form lather with hard water.
5.They are made from natural compounds such as fatty acids or vegetable or animal fats.Detergents are synthetically derived from chemicals.
6.Soap is generally prepared from plant and animal fats through saponification. Petroleum (Petrochemicals) was found to be a plentiful source for the manufacture of detergent.
7.Soaps are not ionic in nature.Detergents may be cationic, anionic, or non-ionic in nature.
8.They are not effective in hard water and saline waterThey do not lose their effectiveness in hard water and saline water.
9.Examples: Sodium StearateExamples: Sodium lauryl sulphate

Sample Questions

Question 1: What are detergents?

Answer:

Detergents are quaternary ammonium or sulfonate salts of long chain of carboxylic acids. Detergents are also known as surfactants as they reduce the surface tension of water. 

Question 2: What are the different types of detergents? And give an example of each type of detergent.

Answer:



The different types of detergents are:

  1. Cationic Detergents: Cetyltrimethylammonium bromide
  2. Anionic Detergents: Sodium lauryl sulphate
  3. Non ionic detergents: Pentaerythrityl stearate

Question 3: What is the major advantage of detergents over soap?

Answer:

The major advantage of detergent over soap is that they are effective for cleaning in hard, saline and acidic water and do not form scum in hard water. Thus detergents are better than soaps in hard water.

Question 4: Why cationic detergents have limited use? Give them one use.

Answer:

Cationic detergents are expensive due to their germicidal properties. Thus they have a limited use. They are used in hair conditioners.

Question 5: Give two disadvantages of detergents.

Answer:

The disadvantages of detergents are:

  • Detergents are expensive as compared to soaps.
  • As the detergents get more and more branched, they become less bio degradable and cause pollution.

Question 6: Define cationic detergents.

Answer:

Those detergents where the polar group is a cation i.e. positively charged are called cationic detergents. Cationic detergents are generally ammonium salts of chlorides, bromides or acetates. The Nitrogen atom in the polar group of these detergents is positively charged.




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