Class 10 science Solutions English Medium

Chapter 4. Carbon and It's Compounds

Soap And Detergents: 

Soaps: The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic-end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles.

Micelles : When soap is at the surface of water, inside water these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.

               The Structure of Micelle

There are important roles of ends of soap molecules for formation of the structure of Micelle. 

The Micelle has two ends:

(i) Hydrophilic end: The end which dissolves in water is called hydrophilic end. 

(ii) Hydrophobic end: The end which dissolves in hydrocarbons (oily substances) is called hydrophobic end. 

Differences between hydrophilic end and hydrophobic end :

Hydrophilic end:

(i) It dissolves in water.

(ii) This is ionic end. 

(iii) The ionic ends are on the surface of the cluster.

Hydrophobic end:

(i) It dissolves in hydrocarbons.

(ii) This is not ionic end. 

(iii) The hydrophobic tails are in the interior of the cluster.

The cleaning process of soap: 

The cleaning process is characterised by soap micelle. The ionic end of soap is dissolves in water and other end dissolves in oily scum and thus forms structure of micelles. Thus micelles are able to clean as soap because oily scums gather in the center of micelles. There forms emulsion in the water. The micelles stay
in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Thus, the dirt suspended in the micelles is also easily removed away and our clothes are cleaned

Micelle properties:

(i) A micelle as soap is able to clean.

(ii) The micelles stay in solution as a colloid.

(iii) These are not precipitated due to ion-ion repulsion.

(iv) Soap micelle can disperse light.

(v) The micelles of soap help to dissolve oily scum in the water.

The soap does not form foam with hard water:

When we wash hand with soap in hard water, we see that foam formed with very difficulty and an insoluble substance (scum) remains after washing with
water. This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence you need to use a larger amount of soap.

The detergent is more effective even in hard water: 

Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water.

Differences between soap and detergent: 

Soap: 

(i) The molecules of soap are sodium or potassium salts of long-chain carboxylic acids.

(ii) It does not form foam in hard water. 

(iii) It increases the hardeness of water. 

(iv) It forms micelle during cleaning process. 

Detergent: 

(i) Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids.

(ii) It form foam even in hard water. 

(iii) It increases the softness of water.

(iv) It does not form micelle during cleaning process.  

Use of detergents: 

(i) Detergents are usually used to make shampoos and products for cleaning clothes.