Question

The molecular mass of acetic acid dissolved in water is $60$ and when dissolved in benzene it is 120. This difference in behaviour of $C{H}_{3}COOH$ is because
(A) Water prevents association of acetic acid.
(B) Acetic acid does not fully dissolve in water.
(C) Acetic acid fully dissolve in benzene
(D) Acetic acid does not ionize in benzene.

Answer 1

Hint: Molecular mass of an element: It is the atomic mass of an element.
Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.

Complete step by step solution:
First of all let us read about molecular formulas.
Molecular mass of an element: It is the atomic mass of an element.
Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.
Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance.
Molecular formula: The molecular composition in the compound is known as molecular formula. For example: the molecule of water is $H_{2}O$ i.e. two atoms of hydrogen with oxygen.
Hydrogen bond: In this type of bond one atom is hydrogen and the other atom is oxygen, nitrogen or fluorine. The bond between these atoms is known as hydrogen bond. For example: water.
Here we are given with the compound acetic acid. The molecular mass of acetic acid is $12+3\times 1+12+16\times 2+1=60$ . And when it dissolves in water then there is dimerization there (when one molecule reacts with other molecule of same type) so its molecular mass remains same. But when acetic acid dissolves in benzene than acetic acid dimerizes (because of the hydrogen bonding in the molecules) and hence its molecular mass becomes double than that of normal molecular mass. Hence we can say that water prevents association of acetic acid.
So option a is correct.

Note: Hydrogen bonds are of two types: Intermolecular and intramolecular hydrogen bonds.
Intermolecular hydrogen bonds: They are formed between two or more different molecules of the same or different types.
Intramolecular hydrogen bonds: They are formed within a molecule.