Question

Give reason for the following observation:
Use of synthetic detergents causes pollution of water.

Answer 1

We know that synthetic detergents are the substances which act as cleansing agents that possess all properties of soap but actually do not contain any form of soap. Their use is not limited like soap. They can be used in both soft and hard water.

Complete step by step answer:
Let’s discuss the disadvantages of using detergents. The hydrocarbon chain of detergents is highly branched due to which bacteria cannot degrade this chain easily. Due to the slow degradation by bacteria results in accumulation. Effluents composed of such detergents reach the water bodies like rivers, ponds etc. These detergents present in water after sewage treatment and result in foaming in rivers, streams and ponds. In this way water bodies get polluted.

Additional Information:
let's discuss soaps in detail. All soaps are manufactured by boiling oils or fats with soluble NaOH. Different types of soaps are manufactured by using different raw materials. The cleansing action of soap is not suitable for hard water. We know hard water contains magnesium and calcium ions. These ions produce magnesium and calcium soaps respectively in addition to potassium or sodium soaps in water.
$2{C_{17}}{{\rm{H}}_{{\rm{35}}}}{\rm{COONa}} + {\rm{CaC}}{{\rm{l}}_{\rm{2}}} \to 2{\rm{NaCl}} + {\left( {{{\rm{C}}_{{\rm{17}}}}{{\rm{H}}_{{\rm{35}}}}{\rm{COO}}} \right)_2}{\rm{Ca}}\,\,\left( {{\rm{insoluble}}\,{\rm{soap}}} \right)$
The formed insoluble soaps separate as scum in water and therefore soap is useless in hard water.
Let's discuss the cleansing action of detergents. As detergents do not contain any soap, so they can be used in both hard and soft water. The formation of foam will take place even in hard water. Moreover some detergents produce foam even in cold water.

Note: Nowadays branching of hydrocarbon chains is controlled and kept at least possible. Due to the less branching of the hydrocarbon chain, bacteria can degrade it easily and in this way pollution of water can be reduced.