Carboxylic Acids Flashcards
Physical properties of Carboxylic acids
1) Colourless solution with sour taste
2) weak acid with pH
Why does boiling point decrease with increase in branching?
Branching gives the molecules a more spherical shape leading to lower surface area for Van der Waal’s interaction and hence reduces Van der Waal’s forces between molecules.
Why do Carboxylic acids have higher boiling points than corresponding alcohols of comparable molecular mass?
Each Carboxylic acid molecule contains a highly polar hydroxyl group which leads to 2 hydrogen bonds between two acid molecules compared to only one hydrogen bond between two alcohol molecules.
Solubility in water of Carboxylic acids
Relatively soluble in water, solubility decreases with increase in molecular size
Solubility decreases as the length of the carbon chain increases, as the polar carboxyl group becomes and ever smaller part of the molecule and the molecule becomes more like a hydrocarbon
Why does solubility of Carboxylic acids decrease at a slower rate than alcohols as molecular size increases?
- presence of carboxyl group enables each Carboxylic acid molecule to form 3 hydrogen bonds with water molecules in exothermic reaction
- with increase in length of carbon chain since carboxyl group can form 3 bonds it is less insignificant as hydroxyl group in alcohols
Manufacture of Carboxylic acids
Same as two ways in which alcohols are oxidized. Carboxylic acids are formed from the oxidation of alcohols.
What are the chemical properties of Carboxylic acids?
1) Same as acids- MASH, BASE and CASCW
2) Combustion (complete and incomplete)
3) Condensation Reaction (Name: Esterification)
Diff between Carboxylic acids and regular acids
Carboxylic acids react less vigorously as they are weak acids and dissociate only partially in water to form hydrogen ions
What is Esterification?
Carboxylic acids react with alcohols to form sweet smelling compounds called esters
What are the conditions required for Esterification?
Heat under reflux, concentrated sulfuric acid as catalyst and dehydrating agent
Diff between forward and backward reaction for Esterification
Forward reaction is condensation (evolves eg loses a water molecule)
Backward reaction is hydrolysis (uses water to form back ethanoic acid)
For condensation reaction, which part is broken off th Carboxylic acid and alcohol?
Carboxylic acid: ALWAYS OH broken off
Alcohol: ALWAYS H broken off
Why is concentrated sulfuric acid important as a dehydrating agent?
It is a strong dehydrating agent which pushes the equilibrium if the reaction forward to result in greater yield of esters by removing the water molecules as they are formed
What are esters?
Esters are organic compounds with characteristic smells that are prepared by reacting alcohol using concentrated sulfuric acid as catalyst
Compare the boiling points of esters with their corresponding Carboxylic acids with the same number of carbon atoms
Esters have lower boiling points than the corresponding Carboxylic acids with the same number of carbon atoms
Why do esters have lower boiling points than Carboxylic acids with the same number of carbon atoms?
- due to absence of hydroxyl group, esters do not form hydrogen bonds between its molecules
- with only Van der Waal’s forces found between ester molecules, it is weaker than hydrogen bonding found between Carboxylic acid molecules
Solubility of esters?
Esters are relatively soluble in water but decreases as molecular size increases
Why are esters relatively soluble in water but decreases with increase in molecular size?
- hydrogen bonds are formed between ester and water molecules with partially positive hydrogen atoms in the water molecules attracted to lone pairs of oxygen atoms on the ester
- Hydrogen portion of the ester molecule force itself between the water molecules and break the relatively strong hydrogen bond as molecular size increases
Uses of ethanoic acid
- food flavoring and preservative
- to make drugs such as aspirin
- bleaching agent in detergent
Uses of citric acid
- natural preservative and anti-oxidant
- used in baking powder to react with sodium bicarbonate to result in the raising action from carbon dioxide formation
Uses of esters
- To prepare cosmetics and perfumes
- artificial favour in processed food and drinks
- used in production of polyesters (synthetic fibers to make textiles)
- found naturally in fruits and flowers
