carboxylic acids and esters

Question 1

what is the name of the carboxylic acid functional group?

Answer 1

carboxyl group (COOH)

Question 2

in their reactions, carboxylic acids can form…

Answer 2

metal salts (carboxylates)

Question 3

solubility: short chain carboxylic acids are…

Answer 3

very soluble in water
- this is because the polar C=O and -OH can form H-bonds with water.

Question 4

solubilty: as chain length increases…

Answer 4

solubility decreases (due to longer non-polar hydrocarbon chain)

Question 5

why do carboxylic acids have a higher b.p compared to alcohols with the same Mr?

Answer 5

due to the formation of DIMERS via hydrogen bonding between two molecules (doubles the size of the molecule)

Question 6

reactions: Carboxylic acids react with bases, alkalis and reactive metals to form…

Answer 6

salts

Question 7

what are the observations during a reaction of carb. acids with carbonates?

Answer 7

effervescence and the solid carbonate will be used up, producing a colourless solution

Question 8

what is the general reaction between a carb. acid and a carbonate?

Answer 8

acid + carbonate → salt + water + carbon dioxide

e.g., * ethanoic acid with sodium carbonate:
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2

e.g., * ethanoic acid with sodium hydrogen carbonate:
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2

Question 9

what are the observations for a reaction between carb. acids and metals?

Answer 9

effervescence and the solid metal will be used up producing a colourless solution

Question 10

what is the general reaction between a carb. acid and a metal?

Answer 10

Acid + metal → salt + hydrogen

e.g., ethanoic acid with magnesium:
2CH3COOH + Mg → (CH3COO)2Mg + H2

Question 11

what are the observations for the reaction between a carb. acid and a base?

Answer 11

release of heat and colourless solution remains

Question 12

what is the general reaction between a carb. acid and a base?

Answer 12

Acid + base → salt + water

e.g., ethanoic acid with sodium hydroxide:
CH3COOH + NaOH → CH3COONa + H2O

Question 13

what are the observations between a carb. acid and ammonia?

Answer 13

a release of heat + the colourless solution remains

Question 14

what is the general reaction between a carb. acid and ammonia?

Answer 14

acid + ammonia → ammonium salt

e.g., ethanoic acid with ammonia:
CH3COOH + NH3 → CH3COONH4
(ammonium ethanoate formed)

Question 15

what is the functional group for esters?

Answer 15

ester group/ester linkage (COO)

Question 16

what is the general structure of esters?

Answer 16

R-C(=O)-O-CR’

R is from the acid
R’ is from the alcohol

Question 17

reacting: carb. acids and alcohols react in the presence of…

Answer 17

heat and a strong acid catalyst (ESTERIFICATION)

Question 18

what is the general reaction for carb. acids and alcohols?

Answer 18

carb. acid + alcohol –> ester + water

Question 19

esterification is an example of…

Answer 19

a (reversible) condensation reaction

Question 20

what are some common uses of esters?

Answer 20

• plasticisers
• solvents for paints, glue, printing inks and nail polish remover
• perfumes
• food flavourings

Question 21

what is the reverse of esterification

Answer 21

hydrolysis
- there are two types: acidic hydrolysis and alkaline hydrolysis

Question 22

what are the conditions for acid hydrolysis?

Answer 22

Catalyst: dilute hydrochloric acid

Conditions: heat under reflux

Products: carboxylic acid + alcohol
* This is a reversible reaction, giving lower yields

Question 23

what are the condition for alkaline hydrolysis?

Answer 23

Catalyst: aqueous sodium hydroxide

Conditions: heat under reflux

Products: carboxylate salt + alcohol
*This is an irreversible reaction, giving higher yields - the alkali
catalyst reacts with the carboxylic acid to form a salt.

Question 24

vegetable oils and animal fats are esters of…

Answer 24

propan-1,2,3-triol (aka glycerol) and three long chain carboxylic acids called fatty acids

Question 25

fatty acids can be...

Answer 25

saturated (no double bond) or saturated (double bond present)

Question 26

what state are fats at room temperature?

Answer 26

Fats are triglycerides that are solid at room temp. - This is because fats are mainly made of saturated fatty acids, which are straight (they can therefore fit neatly together) - This increases the van der Waals’ forces between them, leading to higher m.p

Question 27

what state are oils at room temperature?

Answer 27

Oils are triglycerides that are liquid at room temp. - This is because they mainly have unsaturated fatty acids, which are bent and have kinks that obstructs packing. - This decreases the van der Waals’ forces between them, leading to lower m.p

Question 28

what is saponification?

Answer 28

the alkaline hydrolysis of fats/oils into glycerol + the salts of the fatty acids present in the fat (AKA soaps)

Question 29

what is the general equation for saponification?

Answer 29

fat/oil + 3NaOH --> glyerol (propan-1,2,3-triol) + sodium salt (the soap)

Question 30

what is biodiesel?

Answer 30

a renewable fuel made from vegetable oils such as rapeseed oil, palm oil, and soybean oil

Question 31

use of biodiesel:

Answer 31

can be used in normal diesel engines to power cars/buses

Question 32

what is biodiesel composed of?

Answer 32

a mixture of methyl esters of long-chain carboxylic acids

Question 33

how is biodiesel made?

Answer 33

reacting vegetable oils with methanol in the presence of HEAT and A STRONG BASE CATALYST (e.g., KOH) this process is known as trans-esterification

Question 34

what is trans-esterification?

Answer 34

reacting an ester with an alcohol to produce a different ester and alcohol

Question 35

what is the general equation for trans-esterification?

Answer 35

fat/oil + 3CH3OH --> glycerol + mixture of methyl esters (3 x methyl ester)

Question 36

what are the advantages of biodiesel?

Answer 36

- renewable - carbon neutral

Question 37

what are the disadvantages of biodiesel?

Answer 37

- need lots of farming space to make vegetable oil, crops could be grown for biodiesel production rather than for food leading to food shortages. - Not necessarily carbon neutral - energy is used to make the fertiliser to grow crops (If this energy comes from fossil fuels, then the process won’t be carbon neutral overall)