What is soap? Why are soaps not suitable for washing clothes when water is hard?

Soap:

• Soaps are cleansing agents capable of reacting with water and dislodging the unwanted particles from clothes or skin.
• The molecules of soap are sodium or potassium salts of long chain carboxylic acids.
• A soap molecule has a tadpole-shaped structure.
• At one end (long non-polar end) of soap, a molecule is a hydrocarbon chain which is insoluble in water but soluble in oil.
• At the other end (short polar end) of soap molecule, there is a carboxylate ion which is hydrophilic i.e. water soluble but insoluble in oil.

 

 

 

• Soap on mixing with water forms a concentrated solution and causes foaming.
• The long non-polar end of soap gravitates towards and surrounds the dirt and absorbs the dust in it.
• The short polar end with the carboxylate ion repels the water away from the dirt.
• A spherical aggregate of soap molecules is formed in the soap solution in water and is called a micelle.
• Thus, the soap molecule dissolves the dirt and our clothes get clean.
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 soaps are not suitable for washing clothes when water is hard:

Soaps, when used with hard water, does not lather or produce foam easily because of the formation of a curdy precipitate or scum.

This scum is created when soaps react with the calcium and magnesium ions present in hard water.