Question

Cleansing action of soap occurs because:
(A) oil and grease can be absorbed into the hydrophobic centers of soap micelles and washed away
(B) oil and grease can be absorbed into hydrophilic centers of soap micelles acid washed away
(C) oil and grease can be absorbed into both hydrophilic and hydrophobic centers but not washed away
(D) cleansing action is not related to micelles

Answer 1

Hint: A soap is a compound that is soluble in liquid water produced through the reaction of potassium or sodium hydroxide with oils like animal oils(fats) or vegetable oil in a procedure termed as saponification. A molecule of soap is made up of a continuous sequence of atoms namely carbon, with two ends among which one of them is used for attracting oil and the other one is water attracted.

Complete answer:
Soap molecules are made up of sodium or potassium salts of carboxylic acid chains that are long.
The carbon chain end disintegrates when in oil and the opposite end that is the ionic end decomposes when in water, this is what happens in the case of soaps. As a result, the soap molecules become micelles.
One end of a micelle faces the oil droplet, while the ionic end faces the opposite side of the oil that is outward. In this way, it creates an emulsion of water which aids in the dissolution of impurities when we clean our fabrics.
Taking a look at the options:
Option (A) ‘oil and grease can be absorbed into the hydrophobic centers of soap micelles and washed away‘, this is the correct option. This is because the hydrophobic center is repulsive to dissolve water but has an affinity to dissolve the dirt. Conversely the hydrophilic center is more attracted to water and so dissolves the water, together the hydrophobic and hydrophilic part cleanses the dirt completely.
Option (B) ‘oil and grease can be absorbed into hydrophilic centers of soap micelles acid washed away’, this is an incorrect option. Since the hydrophilic area is non-responsive to dirt but only towards water, it is incorrect to say that the hydrophilic part absorbs the dirt particles.
Option (C) ‘oil and grease can be absorbed into both hydrophilic and hydrophobic centers but not washed away’, this is an incorrect option. This is because hydrophobic part is the only part that can absorb and dissolve the oil and dirt but the hydrophilic part does not attract to dirt, so this cannot be true.
Option (D) ‘cleansing action is not related to micelles’, this is an incorrect option. Here it is definitely wrong to say that soaps have no relation to micelles during the time of cleansing action, since during cleansing action the soap forms micelles that cleanse effectively.
Therefore the correct answer is option (A) ‘oil and grease can be absorbed into the hydrophobic centers of soap micelles and washed away‘, this is the right phenomenon behind cleansing action.

Note:
As the soap gets incorporated into hard water, the hard water's calcium and magnesium ions interfere with the soap. Sodium salts are the part of the soap that functions as cleansers but they get transformed into calcium or magnesium salts when in hard water, hence causing scum as a precipitate. Since the insoluble scum attaches to the fabrics, the cleansing power of the soap is decreased.