If the length of hydrocarbon chain of a detergent was to increase, which of the
ID: 148314 • Letter: I
Question
If the length of hydrocarbon chain of a detergent was to increase, which of the following would be expected to happen?
a) The tendency to form micelles in water will increase and the critical micelle concentration will increase.
b) The tendency to form micelles in water will increase and the critical micelle concentration will decrease.
c) The tendency to form micelles in water will decrease and the critical micelle concentration will increase.
d) The tendency to form micelles in water will decrease and the critical micelle concentration will decrease.
e) None of the above.
Explanation / Answer
The answer is b.
The detergent function is due to the amphipathic structure of the hydrocarbon. Detergents contain hydrophilic head and hydrophobic tail region. This characteristic feature of hydrocarbons allows them to form aggregates in presence of water. The hydrophilic head orients itself towards the polar water molecules while the hydrophobic region orients themselves together to form micelles.
Critical micelle concentration is the concentration at which micelles begin to form. The hydrophobic tails can affect the micelle formation and its structure. As the hydrocarbon chain length increases the size tendency to form micelles increases and the CMC decreases because now fewer molecules are needed to form the micelles.