carboxyllic acids

Question 1

what’s a property of carboxylic acids with very low molecular mass

why?

Answer 1

they are very soluble in water

because the -COOH forms hydrogen bonding with water

Question 2

do carboxyllic acids slightly or strongly dissociate in water

so are they strong or weak

Answer 2

slightly

weak

Question 3

what is formed when carboxyllic acids slightly disassociate

Answer 3

carboxylate ion and hydrogen ion

Question 4

how do carboxylic acids dissociate

Answer 4

the carbonyl group attracts electrons away from the -OH bond, which leads to the -OH bond being weakened therefore it breaks more easily to form a carboxylate ion and hydrogen ion

Question 5

why are alcohols not acidic even if they have OH bond

Answer 5

bc the bond in alcohols doesn’t break easily

Question 6

how does the addition of a halogen onto carboxylic acids changes its acidity

Answer 6

it makes it more acidic

Question 7

why does the addition of a halogen onto carboxylic acids increase its acidity

Answer 7

the halogen atom is more electronegative and so withdraws electron density away from the carbonyl carbon.

this causes the OH bond to become more polar which results in the OH bond weakening .

the H in the OH bond is lost more easily lost so chloroethanoic acid is more acidic than ethanoic acid

Question 8

how do we test for carboxyllic acids

Answer 8

reacting with sodium carbonate Na2CO3

effervescence is observed from CO2

Question 9

eg what is formed when sodium ethanoic acid reacts sodium carbonate

Answer 9

co2 + water + sodium ethanoate

Question 10

what’s formed when carboxylic acids react with alcohol in the presence of concentrated sulphuric acid

what’s the reaction called

Answer 10

ester and water

esterifcation

Question 11

what are 3 uses of esters

Answer 11

flavourings , perfume , plasticisers

Question 12

how do we name esters

Answer 12

alcohol bit then carboxylic acids bit

eg

methyl ethanoate

(methanol+ethanoic acid)

Question 13

how many ways to make esters

Answer 13

3

Question 14

are carboxyllic acids and esters isomers of one another

Answer 14

yes, functional group isomers

same molecular formula different structural formula

Question 15

what are 2 ways the hydrolyse esters

Answer 15

acid hydrolysis

basic hydrolysis

Question 16

how are esters hydrolysed using acid hydrolysis

Answer 16

this is a reversible reaction.

esters can be hydrolysed using water and dilute H2SO4/HCl to form the alcohol and carboxylic acid

Question 17

how do we make hydrolysis complete as possible in acid hydrolysis of ester because it’s a reversible reaction

Answer 17

excess of water

Question 18

as acid hydrolysis of ester is a reversible reaction, this gives a low yield of carboxylic acid and alcohols , therefore there an alternative 2 step method

what is the method

Answer 18

basic hydrolysis

Question 19

what happens in the first step of basic hydrolysis of ester

Answer 19

when an ester is heated with alcohol , it is hydrolysed into an alcohol and carboxylate salt

Question 20

what happens in the 2nd step of basic hydrolysis of ester

Answer 20

we add an excess of dilute HCl or dilute H2SO4 to the carboxylate salt to reform the carboxylic acid

Question 21

how do we make soaps from fats

Answer 21

triglycerides can be hydrolysed using HOT NaOH or KOH to form glycerol (a useful solvent) and sodium or potassium carboxylate salts (these are used to manufacture soaps)

Question 22

whys glycerol a good solvent

Answer 22

it has 3 OH bonds therefore forms hydrogen bonds easily in water

Question 23

definition of biodiesel

Answer 23

liquid fuel consisting of a mixture of methyl esters of long chain carboxylic acids from vegetable oils

Question 24

how do we make biodiesel

Answer 24

the oil is reacted with methanol with a strong acid / alkali catalyst to form a mixture of methyl esters which can be used a fuel in diesel vehicles

the products are mixtures of methyl esters and glycerol

Question 25

carboxylic acids can be turned into other functional groups to be used in organic synthesis. so what 2 groups can be formed from carboxylic acids

Answer 25

acyl chlorides acid anhydrides

Question 26

how are acyl chlorides formed

Answer 26

the -OH group on the carboxylic acid is replaced with a chlorine atom

Question 27

how are acyl chlorides named

Answer 27

CH3COCl is derived from ethanoic acid and therefore it is called ethanoyl chloride

Question 28

the carboxylic acid derivative (acyl chloride) possesses a good leaving group (Cl) which also…

Answer 28

withdraws electrons from the carbonyl carbon making the carbon more reactive

Question 29

what’s a good leaving group

Answer 29

a stable species which is removed during a chemical reaction

Question 30

what reaction do acyl chlorides and acid anhydrous react with nucleophiles

Answer 30

nucleophillic addition elimination and reduction reaction

Question 31

what do the reactions of acyl chlorides and acid anhydrous involve

Answer 31

it involves the replacement of the leaving group eg Cl- by the nucleophile

Question 32

what’s formed when acyl chlorides react with water

Answer 32

carboxylic acids

Question 33

what’s formed when acyl chlorides react with alcohol

Answer 33

esters

Question 34

what’s formed when acyl chlorides react with ammonia

Answer 34

amides

Question 35

what’s formed when acyl chlorides react with amines

Answer 35

substituted amides

Question 36

why are acyl chlorides more preferred in the formation of esters than carboxyllic acids

Answer 36

1) no need for acid catalyst (H2SO4) 2) purer product 3) more yield as reaction isn’t reversible

Question 37

why’s the other carboxylic acid derivative acid anhydrides preferred over acyl chlorides in the formation of esters

Answer 37

1) no corrosive HCl formed 2) acid anhydrides less vulnerable to hydrolysis

Question 38

what’s the -OH group replaced with in carboxylic acids to make acid anhydrides

Answer 38

-OCOR

Question 39

how are acid anhydrides formed

Answer 39

acid anhydrides are formed when 2 molecules of carboxylic acids join together with the elimination of water

Question 40

how do we name acid anhydrides

Answer 40

The acid anhydride is named after the carboxylic acid that was used in its synthesis. then we just add anhydride to the end eg : ethanoic anhydride or ethanoic propanoic anhydride

Question 41

do acid anhydrides have a good leaving group and why what happens when the good leaving group leaves

Answer 41

yes acid anhydrides good leaving group is - ➖OCOR because a leaving group is a stable species that is removed during a chemical reaction when the good leaving group leaves it activates the adjacent carbonyl group by electron withdrawal

Question 42

acid anhydrides react with the same nucleophiles as acyl chlorides to form the same products which are…

Answer 42

water to form carboxylic acids alcohols to form esters ammonia to form amides amines to form substituted amides

Question 43

acyl chlorides and acid anhydrides react in the same way as their corresponding carboxylic acid but ….

Answer 43

will produce a different side product eg acid anhydrides and alcohol = ester and carboxylic acids eg acyl chloride and alcohol= ester and HCl eg carboxylic acid and alcohol = ester and H2O

Question 44

what do acid anhydrides react with to form carboxyllic acids

Answer 44

water (nucleophillic addition elimination mechanism too)

Question 45

what are the 3 ways to make carboxylic acids

Answer 45

1) primary alcohols / aldehydes oxidised by acidified potassium dichromate to form carboxylic acids and water 2) acyl chlorides and water to form carboxyllic acids and HCl 3) acid anhydrides and water to form 2 molecules of carboxylic acids

Question 46

how do acid anhydrides react with to form esters

Answer 46

with alcohol

Question 47

what are 3 ways to make esters

Answer 47

1) carboxylic acid and alcohol (esterifcation) 2) acyl chloride and alcohol 3) acid anhydrides and alcohol