Question

Soaps cannot be used in hard water because they:
A) Contain sodium
B) Form precipitate
C) Create environmental problems
D) Create ozone depletion

Answer 1

The soap has two parts, hydrophobic and hydrophilic, which are responsible for the interaction of the soap molecules with water.
Hardness of water is caused by the presence of certain dissolved minerals like magnesium and calcium salts in water.

Complete answer:
In order to answer this question we must know the definition of each of the terms which are used in the question. At first, we would look at the definition of soap, which is long chain fatty acids which have two parts, a hydrophilic and a hydrophobic part. The long non-polar carbon chain tends to repel the water hence it is hydrophobic, while on the other hand the carbonic acid group at the end of the carbon chain tends to attract water in order to form hydrogen bonds with the molecules of water, hence hydrophilic. Ideally, when soap is added to the water, the oil or dirt which is in the water, the hydrophobic part gets attached to the oil or dirt and the hydrophilic part will attract the water molecules.
Now, we will jump to the next definition which is hard water. It is the type of water which contains calcium and magnesium salts dissolved in it. While soft water is, distilled water or pure water which doesn’t contain any minerals.
Soaps cannot be used in hard water because of its tendency to form precipitate with those calcium and magnesium salts which are present in hard water. This formation of precipitate results in prevention of formation of lather in soap water. This can be prevented by the addition of some other chemicals like sodium silicate or borax etc. to the hard water, as addition of these minerals would prevent the soap from combining with the minerals which are present in hard water, consequently preventing formation of precipitate.

Hence the correct option would be option B.

Note: The addition of soap in hard water results in formation of precipitate of that soap because of the presence of calcium and magnesium salts present in the hard water. In case of soft water, soap forms a lather and it uses a certain mechanism to get rid of the dirt present in the water, as it traps the dirt molecules and forms scum as a result.