Question

Which of the following indicates the number of free $-OH$ groups in an oil or fat
A. Iodine value
B. Acid value
C. Acetyl value
D. Saponification value

Answer 1

Hint: To answer this question we have to know about acetyl value of fat and oil. The acetyl value of fat and oil is defined as the number of grams of potassium hydroxide required to neutralise the acetic acid that is formed by the acetylated fat or oil.

Complete Step by Step Solution:
The acetyl value of fat and oil is defined as the number of grams of potassium hydroxide required to neutralise the acetic acid that is formed by the acetylated fat or oil. It determines the number of hydroxyl groups.

The saponification value of oil is defined as the number of one milligram of potassium hydroxide required to neutralise one gram of the oil or fat obtained by the hydrolysis of the sample.

The acid value is defined as the number of one milligram of potassium hydroxide required to neutralise one gram of the oil or fat. Thus we can write that the number of free hydroxyl groups in a fat or oil is determined by acetyl value.
Thus the correct option is C.

Additional information: An oil is a nonpolar substance. It is composed primarily of hydrocarbons. It can be both hydrophobic and lipophilic. Oils are usually flammable and surface active substances. Most of the oils are unsaturated lipids that are present as a liquid at room temperature. Fats have the same property as oil but it exists as a solid at room temperature. Both fat and oil are made of glycerol.

Note: The acetyl value of oil and fat is determined using basic potassium hydroxide. It determines the number of hydroxyl groups.