Hydrogen bonding plays a central role in the following phenomena:a)Ice floats in waterb)Higher Lewis basicity of primary amines than tertiary amines in aqueous solutionsc)Formic acid is more acidic than acetic acidd)Dimerisation of acetic acid in benzeneCorrect answer is option 'A,B,D'. Can you explain this answer?

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Hydrogen bonding plays a central role in the following phenomena:

a) Ice floats in water:
- When water freezes, the hydrogen bonds between water molecules become more ordered and stable.
- The water molecules arrange themselves in a hexagonal lattice structure, with each water molecule forming four hydrogen bonds with its neighboring molecules.
- These hydrogen bonds create an open, hexagonal structure, which causes the solid ice to be less dense than the liquid water.
- As a result, ice floats in water because it is less dense.

b) Higher Lewis basicity of primary amines than tertiary amines in aqueous solutions:
- Primary amines contain a nitrogen atom bonded to two hydrogen atoms and one alkyl group, while tertiary amines have three alkyl groups bonded to the nitrogen atom.
- In aqueous solutions, primary amines can form hydrogen bonds with water molecules through their lone pair of electrons on the nitrogen atom.
- These hydrogen bonds enhance the solubility of primary amines in water and increase their Lewis basicity.
- On the other hand, tertiary amines do not have a hydrogen atom directly bonded to the nitrogen atom, so they cannot form as many hydrogen bonds with water molecules.
- Therefore, the Lewis basicity of primary amines is higher than that of tertiary amines in aqueous solutions.

c) Formic acid is more acidic than acetic acid:
- Both formic acid and acetic acid contain a carboxylic acid group (-COOH) which can donate a proton (H+) in an acid-base reaction.
- However, formic acid is more acidic than acetic acid due to the presence of the hydrogen atom directly bonded to the carbonyl carbon in formic acid.
- The hydrogen atom in formic acid is more acidic because it is more easily ionizable due to the inductive effect of the electronegative oxygen atom in the carboxylic acid group.
- This inductive effect stabilizes the conjugate base of formic acid, resulting in a stronger acid compared to acetic acid.

d) Dimerization of acetic acid in benzene:
- Acetic acid can form dimers in non-polar solvents such as benzene due to hydrogen bonding between two acetic acid molecules.
- In the dimer, the oxygen atom of one acetic acid molecule forms a hydrogen bond with the hydrogen atom of the other acetic acid molecule.
- This hydrogen bonding interaction stabilizes the dimer and allows acetic acid to exist as dimers in benzene.
- The formation of these dimers is driven by the favorable energy associated with hydrogen bonding.
- Hydrogen bonding plays a central role in the dimerization of acetic acid in benzene.

Similar Chemistry Doubts

One molal solution of a carboxylic acid in benzene shows the elevation of boiling point of 1.518 K. The degree of association for dimerization of the acid in benzene is (Kb for benzene = 2.53 K kg mol1)

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