A soap is the sodium or potassium salt of a long chain carboxylic acid
Example : ` C_(17) H_(35) COO-Na^(+)` Sodium stearate
`C_(15) H_(31) COO^(-) Na^(+)` Sodium palmitate
A detergent is ammonium or sulphonate salt of a long chain carboxylic acid
Example: `CH_(3) - (CH_(2))_(11) - C_(6) H_(4) - SO_(3) ^(-) Na^(+)`
`CH_(3) - (CH_(2))_(10) - CH_(2) - SO_(4) ^(-) Na^(+)`
Cleansing action of soaps . One part of soap molecule is ionic/ hydrophilic and dissolves in
water . The other part is non-ionic,i.e., the carbon
chain which is hydrophobic and dissolves in oil.
Thus, the soap moleculars arrange themselves in the
shape of a micelle.
On rinsing with water the soap is washed off, lifting
the oily dirt particles with it.
Soaps doe not form lather in hard water . Soaps are
sodium slats of fatty acids . Fatty acids are a type of
carboxylic acids with long chain of carbon atoms.
Soaps are not suitable for washing clothes when the water is hard:
The formation of lather is necessary for
removing dirt from clothes durings the washing of clothes. Soap does not give lather
with hard water as it reacts with the calcium and magnesium ions present in hard
water to form insoluble preciptates of calcium and magnesium salts of fatty acids.
The scum (or precipitate) formed by the action of hard water on soap sticks to the
clothes being washed and it interferes with cleaning ability of soap. This makes
the cleaning of clothes difficult.
Problems that arise due to the use of detergents instead of soaps:
(i) Detergents are non-biodegradable, .i.e., they cannnot be decomposed by micro-
organisms and hence cause water pollution in lakes and revers .
(ii) Datergents can also cause skin problems.
