People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Agitation is necessary to get clean clothes because most dirt is oily in nature and does not dissolve in water. Soap molecules form micelles where the hydrophobic end interacts with oil and the hydrophilic end interacts with water. The oily dirt is collected in the centre of these micelles.
Agitation helps in the formation of micelles by bringing soap molecules in contact with the oily dirt on clothes. It also helps in creating an emulsion in water, which allows the soap micelles to effectively pull out the dirt.
The mechanical action of beating, scrubbing or agitation ensures that micelles are properly formed around the dirt particles and helps dislodge the dirt from the fabric, allowing the clothes to be washed clean.
Explanation
The textbook explains that soap molecules have two ends with differing properties - one is hydrophilic (interacts with water) and the other is hydrophobic (interacts with hydrocarbons/oil). These molecules form micelles where the oily dirt is collected in the centre. The micelles stay in solution as a colloid. Agitation is necessary because it facilitates the formation of micelles by ensuring contact between soap molecules and oily dirt. It also helps create an emulsion and mechanically dislodges dirt from the fabric surface.