Question

What is the purpose of the ethanol in the saponification reaction?

a. It catalyzes the saponification process.

b. It helps prevent the fat from reacting with oxygen in the air.

c. It reduces the flammability of the reaction mixture.

d. It raises the boiling point of the mixture, which speeds up the saponification reaction.

e. It is less polar than water and helps to dissolve the nonpolar fat so that it can react with the sodium hydroxide.

Answer 1

Ans. Correct option. E.

Saponification reaction:       Fatty acid + NaOH ----> Na-salt of FA (soap)

In saponification reaction, the hydrophobic fatty acids react with hydrophilic NaOH. Being hydrophobic, the fatty acids are insoluble in aqueous solution of NaOH.

Ethanol (C₂H₅OH) is an amphipathic molecule – the hydrocarbon chain (C2H5) is hydrophobic whereas the hydroxyl group (-OH) is hydrophilic. The hydrophobic group (C2H5) interacts with hydrophobic fatty acids and –OH group interacts with aqueous environment. Thus, ethanol brings both the hydrophobic FA and hydrophilic NaOH is the same phase. Creation of one-phase reactants thus makes the reaction feasible and increases the rate of reaction.

If the FA and NaOH would be insoluble or in two different phases, the reaction would occurs at very low rate.