Aldehyde Ketones And Carboxylic Acids

Question 1

Methanal is gas at room temperature
Ethanal is volatile liquid

Answer 1

Both are correct

Question 2

Lower aldehydes have sharp pungent odours
As the size of molecules increases the odour becomes less pungent and more fragrant

Answer 2

Both are correct

Question 3

Formaldehyde is well known as formalin (40%) solution used to preserve biological specimens and to prepare bakelite (a phenol-formaldehyde resin), urea-formaldehyde glues and other polymeric products

Answer 3

True

Question 4

Benzaldehyde is used in perfumery and in dye industries.

Acetone and ethyl methyl ketone are common industrial solvents.

Answer 4

Both are correct

Question 5

Statement 1: Some higher members of aliphatic carboxylic acids (C12 – C18) known as fatty acids, occur in natural fats as esters of glycerol. Statement 2: Carboxylic acids serve as starting material for several other important organic compounds such as anhydrides, esters, acid chlorides, amides, etc.

Answer 5

Both are correct

Question 6

Statement 1: Aliphatic carboxylic acids upto nine carbon atoms are colourless liquids at room temperature with unpleasant odours.
Statement 2: The higher acids are wax like solids and are practically odourless due to their low volatility

Answer 6

Both are correct

Question 7

Assertion: Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses.
Reason: This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding.

Answer 7

Both are correct and R is correct explanation of A

Question 8

Simple aliphatic carboxylic acids having upto four carbon atoms are miscible in water due to the formation of hydrogen bonds with water.

Carboxylic acids are also soluble in less polar organic solvents like benzene, ether, alcohol, chloroform, etc.

Answer 8

Both are correct

Question 9

Assertion: The solubility decreases with increasing number of carbon atoms.
Reason: Higher carboxylic acids are practically insoluble in water due to the increased hydrophobic interaction of hydrocarbon part.

Answer 9

Both are correct and R correctly explains A

Question 10

The pKa of hydrochloric acid is –7.0, where as pKa of trifluoroacetic acid (the strongest carboxylic acid), benzoic acid and acetic acid are 0.23, 4.19 and 4.76, respectively.

Answer 10

True

Question 11

Strong acids have pKa values < 1.
The acids with pKa values between 1 and 5 are considered to be moderately strong acids.
Weak acids have pKa values between 5 and 15, and extremely weak acids have pKa values >15.

Answer 11

All are correct statements

Question 12

Explain why carboxylate ion is more stabilised than phenoxide ion, so carboxylic acids are more acidic than phenols.

Answer 12

The higher acidity of carboxylic acids as compared to phenols can be understood similarly. The conjugate base of carboxylic acid, a carboxylate ion, is stabilised by two equivalent resonance structures in which the negative charge is at the more electronegative oxygen atom. The conjugate base of phenol, a phenoxide ion, has non-equivalent resonance structures in which the negative charge is at the less electronegative carbon atom. Therefore, resonance in phenoxide ion is not as important as it is in carboxylate ion.

Question 13

…………….is used in rubber, textile, dyeing, leather and electroplating industries.

Answer 13

Methanoic acid

Question 14

…………is used as solvent and as vinegar in food industry.

Answer 14

Ethanoic acid

Question 15

Hexanedioic acid is used in the manufacture of……….

Answer 15

nylon-6, 6

Question 16

Esters of benzoic acid are used in perfumery.
Sodium benzoate is used as a food preservative.
Lower fatty acids are used for the manufacture of soaps and detergents.

Answer 16

Statement 1 and 2 are correct and 3 is incorrect
Higher fatty acids are used for the manufacture of soaps and detergents.