Carboxylic Acids And Derivitives

Question 1

How do you name carboxylic acid with two carboxylic group

Answer 1

If there are carboxylic acid groups on both ends of the chain then it is called a - dioic acid

Question 2

Can carboxylic acids dissolve in water

Answer 2

‘The smaller carboxylic (up to C4) acids dissolve in water in all proportions but after this the solubility rapidly reduces. They dissolve because they can hydrogen bond to water

Question 3

Why is propanoic acid less acidic than ethanoic acid

Answer 3

Increasing chain length pushes electron density on to the COO- ion,
making it more negative and less stable.
This make the acid less strong.

Question 4

Why is chloroethanoic more acidic than ethanoic acid

Answer 4

Electronegative chlorine atoms withdraw- electron density from the COO ion,
making it less negative and more stable.
This make the acid more strong

Question 5

How can methanol acid undergo oxidation

Answer 5

Unlike other carboxylic acids ,methanoic acid contains an an aldehyde group

Question 6

How are esters formed

Answer 6

When carboxylic acid reacts with an alcohol in the presence of a strong catalyst

Question 7

How are esters named

Answer 7

The bit ending -yl comes from the alcohol that has formed

The -snore come from the carboxyl group

Question 8

What are the uses of esters

Answer 8

For perfumes

Used as solvents

Used as plasticisers

Question 9

Describe the hydrolysis of esters

Answer 9

They can be hydrolysed and split by either heating with an acid or with sodium hydroxide

Using
Reagents:dilute HCL
Conditions:heat under reflux

Question 10

Describe hydrolysis of esters using sodium hydroxide

Answer 10

Using excess sodium hydroxide ensures the ester is completely hydrolysed

Reagent:dilute sodium hydroxide
Conditions:heat under reflux

Question 11

Why is the reaction irreversible when using a sodium hydroxide reagent in hydrolysis of esters

Answer 11

The carboxylic acid salt produced is an anion
The anion is resistant to attack by weak nucleophiles
So reaction is not reversible

Question 12

What are fats and oil comprised of

Answer 12

Glycerol and long chain carboxylic acids

Question 13

What is the formula for glycerol

Answer 13

Propan-1,2,3-triol

Question 14

Is glycerol soluble

Answer 14

Forms hydrogen bonds easily
So very soluble

Question 15

What is formed when vegetable oil is hydrolysed

Answer 15

Soap
Glycerol
Long chain carboxylic acid

Question 16

Why can water and soap mix

Answer 16

-Long chain carboxylic fatty acids ,produced by the hydrolysis of fats
- the polar CO2- end is hydrophilic and mixes with water
-the long non-polar hydrocarbon chain is hydrophobic
-allows grease and water to mix

Question 17

What is used to hydrolyse vegetable oils

Answer 17

-KOH

Question 18

What is biodiesel

Answer 18

A mixture of methyl esters of long chain of carboxylic acids

Question 19

How can vegetable oil be converted into biodiesel

Answer 19

Reaction with methanol and vegetable oil in the presence of catalyst

2CH3OH

Question 20

Why are acyl chlorides more reactive than carboxylic acids

Answer 20

The -Cl and -OCOCH3 are good leaving groups

Question 21

How is aspirin formed

Answer 21

When 2-hydroxybenzoic acid reacts ethanoic anhydride

Forming an ester
CH3COH

Question 22

why is inportnat to dissolve the impure compound in a minimum volume of hot solvent

Answer 22

Minimum volume:
To obtain a saturated solution and to enable crystallisation
Hot solvent :
To dissolve compound and the impurities

Question 23

Why is the filtration of solution through filter paper

Answer 23

Removes any insoluble impurities
Will prevent crystals reforming during filtration

Question 24

Why is filtered solution cooled in ice

Answer 24

So crystals will reform
soluble impurities remain in solution
Ice will increase the yield of crystals

Question 25

Why is it important to wash the crystals with distilled water

Answer 25

To remove soluble impurities

Question 26

How is there loss of yield during process

Answer 26

-crystals lost when filtering
-some products stays in solution after recrystallisation

Question 27

How is the degree of purity tested

Answer 27

By determining the melting point

Question 28

What happens to the melting point if impurities are present

Answer 28

The melting point is lowered
The sample will melt over a range of several degrees