Question

What traps the oily dirt during cleansing of dirty fabrics with soap?

Answer 1

• A soap molecule is made up of the following two components:
  • A polar component made up of ${\mathrm{COO}}^{-}{\mathrm{Na}}^{+}$. It is water-soluble. This is referred to as the polar end.
  • A nonpolar component made up of a long chain of 12 to 18 carbon atoms and it is water repellent and oil soluble. This is referred to as the hydrocarbon end.
• When an oily (dirty) piece of cloth is immersed in a soap solution, the hydrocarbon half of the soap molecule bonds to the oily drop while the $-{\mathrm{COO}}^{-}$ end orients itself towards the water.
• The ${\mathrm{Na}}^{+}$ ions in the solution organise themselves around the $-{\mathrm{COO}}^{-}$ ions.
• The negatively charged micelle that forms entraps the greasy dirt.
• Electrostatic repulsion causes the negatively charged micelles to repel each other.
• As a result, the microscopic oily filth particles do not stick together and are rinsed away in water during rinsing.

Therefore, Micelles traps the oily dirt during the cleansing of dirty fabrics with soap.