Aldehydes, ketones and carboxylic acid

Question 1

Production of aldehydes

Answer 1

Made by the oxidation of primary alcohol with acidified potassium permanganate or acidified potassium dichromate, Can be isolate through distillation as it has the lowest boiling point, Readily undergoes oxidation

Question 2

Melting and boiling point of aldehydes

Answer 2

Higher than corresponding alkanes but lower than corresponding alcohol due to the strongest IMF present in each
Alkane IMF- dispersion, Alcohol IMF- dispersion, dipole-dipole, hydrogen
Aldehyde- dispersion, dipole-dipole
As chain length increases, melting and boiling point increase due to increased dispersion forces

Question 3

Solubility of aldehydes in water

Answer 3

Small aldehydes are soluble in water as they form hydrogen bonds with the water, As chain length increases, solubility decreases due to the increased dispersion forces which overpower the hydrogen bond (4-5 chain length)

Question 4

Solubility of aldehydes in organic solvents

Answer 4

Large aldehydes are soluble in organic solvents, As chain length increases, solubility increases due to the increased dispersion forces (forms dispersion forces with organic solvent)

Question 5

Aldehyde reactions

Answer 5

Undergo combustion reactions, Undergo oxidation with strong oxidising agents such as acidified potassium permanganate or acidified potassium dichromate (RCHO —> RCOOH)

Question 6

Production of ketones

Answer 6

Made by the oxidation of secondary alcohols with acidified potassium permanganate or potassium dichromate

Question 7

Melting and boiling point of ketones

Answer 7

Higher than corresponding alkane but lower then corresponding alcohol due to main/strongest IMF present
Alkanes main IMF- dispersion, Alcohols main IMF- hydrogen, Ketones main IMF- dipole-dipole
As chain length increases, melting and boiling point increase due to increased dispersion forces

Question 8

Solubility of ketones in water

Answer 8

Small ketones are soluble in water as they form hydrogen bonds with water, As chain length increases, solubility decreases as dispersion forces become stronger than the hydrogen bonds

Question 9

Solubility of ketones in organic solvents

Answer 9

Large ketones are soluble in organic solvents as they have high dispersion forces, As chain length increases, solubility increases due to increased dispersion forces

Question 10

Ketone reactions

Answer 10

Undergo combustion reactions, Can’t be oxidised by acidified potassium permanganate or acidified potassium dichromate due to the difficulty of breaking a carbon-carbon bond

Question 11

Preparation of carboxylic acids

Answer 11

Made by the oxidation of primary alcohols or aldehydes with strong oxidising agents (acidified potassium permanganate and potassium dichromate), RCH2OH —> RCOOH, RCHO —> RCOOH

Question 12

Melting and boiling points of carboxylic acids

Answer 12

Higher than most organic compounds as it forms a dimer structure (doubled molar mass, increasing dispersion forces and hydrogen bonding), As chain length increases, melting and boiling point increases due to increased dispersion forces

Question 13

Solubility of carboxylic acids in water

Answer 13

Small carboxylic acids are soluble in water as they easily form hydrogen bonds with the water, As chain length increases, solubility decreases due to increased dispersion forces that overcome the strength of the hydrogen bonds

Question 14

Solubility of carboxylic acids in organic solvents

Answer 14

Large carboxylic acids are soluble in organic solvents as they readily form dispersion forces, As chain length increases, so does solubility

Question 15

Strength of carboxylic acids

Answer 15

Weak acids, RCOOH + H20 <—> RCOO- + H3O+, As chain length increases, strength of the acid decreases as it becomes more non-polar

Question 16

Carboxylic acid reactions

Answer 16

Neutralisation: Acid + base —> Salt + water, Acid + carbonate/hydrogencarbonate —> salt + water + carbon dioxide
Oxidation reactions: Acid + reactive metal —> Salt + hydrogen gas