Question

Which part of the soap $\left(RCO{O}^{-}\right)$ dissolves grease and forms micelle ?

• A. $R$ part (called tail of the anion)
• B. $CO{O}^{-}$ part (called head of the anion)
• C. both A and B
• D. none of these

Answer 1

Answer: (C)

both A and B

Both detergent and soap have the same action on grease. Their non-polar tails bond with the non polar grease creating a micelle with the polar head exposed. This polar surface micelle mixes easily with water and the grease can be removed.

When a soap or detergent is added to water that contains oil or other water insoluble materials (e.g. when doing the washing up, washing clothes or at bath time, etc), the soap or detergent molecules surround the oil droplets. The oil or grease is "dissolved" in the alkyl groups of the soap molecules (the oil and dirt are dragged off the dirty dishes, clothes or people) collected together into clumps (micelles) while the ionic end allows the micelle to dissolve in water, and be washed down the drain.

Here $RCO{O}^{-}$ is alkyl group.