Carboxylic Acids

Question 1

Functional group for carboxylic acids

Answer 1

R-COOH

Question 2

Describe the acidity of carboxylic acids

Answer 2

Weak acids

Question 3

Give the formula for the carboxylate ion

Answer 3

COO-

Question 4

Why is the carboxylate ion stable

Answer 4

Negative charge delocalised across the 2 oxygen atoms

Question 5

Describe the melting/boiling points of carboxylic acids

Answer 5

High due to hydrogen bonding between each other

Question 6

Describe the solubility of carboxylic acids

Answer 6

Soluble in water but solubility decreases with chain length

Question 7

How do you test for carboxylic acids

Answer 7

Add NaCO3 - effervescence due to neutralisation and release of CO2

Question 8

How can carboxylic acids be produced

Answer 8

• Oxidising primary alcohols/aldehydes using potassium dichromate (Cr2O72-)
• Esters - Acid Hydrolysis under reflux with dilute HCl
• Acyl Chlorides - H2O - nucleophilic addition
• Nitriles - Reflux with dilute HCl (acid hydrolysis)

Question 9

Describe the reduction of carboxylic acids

Answer 9

• Use LiAlH4 in dry ether
• RCOOH + 4[H] -> RCH2OH + H2O
• Goes straight to primary alcohol

Question 10

Describe the formation of acyl chlorides

Answer 10

• Use PCl5
• RCOOH + PCl5 -> RCOCl + POCl3 + HCl
• Anhydrous conditions as acyl chloride reacts with water to form carboxylic acid
• Use distillation to seperate products

Question 11

What is the observation for HCl

Answer 11

Steamy white fumes

Question 12

Describe the neutralisation of carboxylic acids

Answer 12

Form salt, water and possibly CO2

Question 13

Describe the esterification of carboxylic acids

Answer 13

• Use alcohol and conc. H2SO4

* RCOOH + ROH <=> R-COO-R + H2O

Question 14

Give the general formula for acyl chlorides

Answer 14

RCOCl

Question 15

Describe the reaction of acyl chlorides with water

Answer 15

ROCl + H2O -> RCOOH + HCl
Hydrolysis
Violent reaction
At room temp.

Question 16

Describe the reaction of acyl chlorides with alcohols

Answer 16

RCOCl + R-OH -> RCOOR + HCl

* Non reverisble but produces HCl

Question 17

Describe the reaction of acyl chlorides with Ammonia

Answer 17

RCOCl + 2NH3 -> R-CO-NH2 + NH4Cl

Question 18

What is the observation for Ammoninum Chloride

Answer 18

White smoke

Question 19

Describe the reaction of Acyl chlorides with primary amines

Answer 19

R-COCl + 2R-NH2 -> RCONHR + RNH3Cl

* Produces secondary amine and amine salt

Question 20

Purpose of H2SO4 when producing esters

Answer 20

• Speeds up reaction (catalyst)

- Dehydrating agent of removes water and shifts equilibrium to right

Question 21

Describe the solubility of esters

Answer 21

Small esters are soluble in water due to hydrogen bonding with water molecules

Question 22

Give the general names for esters

Answer 22

(alcohol chain)yl(acid chain)oate

Question 23

What type of polymerisation forms polyesters?

Answer 23

Condensation Polymerisation

Question 24

Describe the formation of polyesters

Answer 24

• Dicarboxylic acids + Diols

* H2SO4 catalyst

Question 25

Advantages and disadvantages of using Diacyl Chlorides to form polyesters

Answer 25

• More reactive so no catalyst needed
• Not a reverisble reaction
• But HCl rather than H2O produced

Question 26

Describe the acid hydrolysis of esters

Answer 26

Ester + Water <=> Alcohol + Carboxylic Acid
Dilute HCl used
You get full acid produced

Question 27

Describe the alkaline hydrolysis of esters

Answer 27

Ester + Water <=> Alcohol + Carboxylate Salt
Add H+ ions to produce full acid
Carboxylate Salts used to make soap