20 — alcohols, carboxylic acids and esters

Question 1

Formation of ethanol

Answer 1

1. Catalytic addition of steam to ethene
   - Reagent: steam H2O
   - Conditions: 300dgC, 60atm, phosphoric(V) acid (H2PO4) catalyst

[C2H4 (g) + H2O (g) —(300dgC, 60atm, H3PO4)—> C2H5OH (l)]
- ethene required here is usually obtained from refining and cracking of crude oil and thus not sustainable as it requires finite resources.

2. Fermentation of glucose
   - alcohol fermentation is a process in which micro-organisms such as yeast act on carbohydrates like glucose in the absence of oxygen to produce ethanol and CO2.

[C6H12O6 (aq) —(yeast, 37dgC)—> 2 C2H5OH (aq) + 2CO2 (g)
- slower than 1st method but more sustainable as starting materials obtained from plants n r renewable resources
- yeast is an enzyme n thus has an opt. Tempt

Question 2

Alcohols

Answer 2

Are organic compounds with the hydroxyl (-OH) functional group

General formula: CnH(2n+1)OH

Question 3

Obtaining glucose in a lab

Answer 3

1. Mix the glucose solution and yeast in a conical flask, w tempt remaining constant at below 36dgC
2. The mass of the conical flask and its contents decreases aft a week due to the release of CO2 2gas
3. Fractional distillation needs to be conducted to eparate ethanol from the mixture

Question 4

Physical properties of alcohols

Answer 4

1. Volatility:
   Shorter-chain alcohols r volatile liquids at rtp.
2. Melting and boiling point:
   There is a gradual increase in mp and boiling point (bp) of alcohols down the homologous series due to increase in molecular size and hence stronger intermolecular forces of attraction.
3. Solubility:
   Decreases down the homologous series as carbon chain increases in length

Question 5

Chemical properties of alcohols

Answer 5

1. Combustion
   Complete combustion produces CO2 and H2O
   [alcohol + oxygen -> carbon dioxide + water]

Eg
2CH3OH (l) + 3O2(g) -> 2CO2(g) + 4H2O(g)

2. Oxidation
   - happens for alcohols w hydroxyl group bonded to a terminal carbon atom

Reagent: Oxidising agent eg ACIDIFIED KMnO4
Conditions: heat
Eg
Ethanol + 2[O] -heat-> Ethanoic acid + H2O

(Loses 2 H, gains 1 O).

3. Has the hydroxyl functional group (—OH) but this group does not dissociate to form OH- ions in water. Hence, alcohol s not a base and esterification is not an acid-base reaction)

Question 6

Carboxylic acids

Answer 6

Are organic compounds with the carboxyl (—COOH) functional group

General formula: CnH(2n+1)COOH

Question 7

Physical properties of carboxylic acids

Answer 7

1. Melting and boiling points
   - Higher compared to alcohols and hydrocarbons w the same number of carbon atoms
   - increases down the homologous series as molecular size increases
2. Solubility
   All soluble in water

Question 8

Chemical properties of carboxylic acids

Answer 8

1. Weak acids that partially ion isles in water to form a carboxylate ion and hydrogen ion
   Carboxylic acid <—> carboxylate ion + hydrogen ion

RCOOH (aq) <—> RCOO- (aq) + H+ (aq)

Question 9

Carboxylic acid reaction with reactive metals

Answer 9

Carboxylic acid + reactive metal -> carboxylate salt + hydrogen

Observations: Effervescence observed, metal dissolved
Test for gas: gas evolved extinguishes lighted splint with a ‘pop’ sound

Eg: ethanoic acid + Mg
2CH3COOH (Aq) + Mg (s) -> (CH3COO)2Mg (aq) + H (g)

Question 10

Carboxylic acid reaction with carbonates

Answer 10

Carboxylic acid + carbonate -> carboxylate salt + CO2 + H2O

Observations: effervescence observed
Test for gas: gas evolved forms white precipitate in limewater

Eg: Na2CO3 + methanoic acid
2HCOOH (aq) + Na2CO3 (s) -> 2HCOONa (aq) + CO2 (g) + H2O (g)

Question 11

Carboxylic acid reaction w bases

Answer 11

Carboxylic acid + bases -> carboxylate salt + water

Eg: CaOH + propanoic acid
2CH3CH2COOH (aq) + Ca(OH)2 (s) -> (CH3CH2COO)2Ca (aq) + 2H2O (l)

(Carboxylic acid loses 1H)

Question 12

Carboxylic reaction w alcohols

Answer 12

Carboxylic acid + alcohol <—> ester + water

Question 13

Formation of ethanoic acid

Answer 13

1. Formed by oxidation of ethanol thru atm O2 and acidified KMnO4
2. Colourless liquid at rtp
3. Used as a preservative and flavouring in food

A. Oxidation of ethanol by atmospheric oxygen
C2H5OH (aq) + O2 (g) —(bacteria)—> CH3COOH(aq) + H2O (l)

B. Oxidation of ethanol by acidified potassium manganate (VII)
CH3CH2OH (aq) + 2 [O] —(heat)—> CH3COOH (aq) + H2O (l)
Observations: purple acidified KMnO4 solution turns colourless

(Ethanol loses 2 H but gains 1 O in both reactions)

Question 14

Esters

Answer 14

Definition: esters are organic compounds formed by the reaction of alcohols and carboxylic acids

Characteristics:
1. Compounds with small molecular sizes
2. Volatile
3. Generally have sweet smells
4. Have ester functional group (-COO-) aka ester linkage
5. General formula: CnH2n+1COOCmH2m+1

C=O side is carboxylic acid
O side is alcohol

Examples: fats
Contain 3 ester functional groups aka triesters
Formed when a compound with 3 hydroxyl groups (-OH) groups react w carboxylic acids

Question 15

Formation of esters

Answer 15

Reagent: Carboxylic acid and alcohol
Conditions: heat, concentrated Sulfuric acid as catalyst

Carboxylic acid + alcohol <—(concentrated H2SO4)—> ester + water

Alcohol loses 1 H, carboxylic acid loses 1 H and 1 O

Aka esterification reaction or condensation reaction (backward reaction) due to the reaction betw 2 molecules to form a single molecule w the loss of a water molecule
Note: NOT acid-base reaction

Question 16

Naming esters

Answer 16

*Alcohol comes first

Name of carbon atom in each alcohol:
1: Methyl
2: Ethyl
3: Propyl
4: Butyl

Name of carbon atom in each Carboxylic acid:
1: Methanoate
2: Ethanoate
3: Propanoate
4: Butanoate

Question 17

Ethanol can be made on an industrial scale by reacting ethene with steam in a reactor. The ethene is mixed with steam and entered the reactor.
C2H4 (g) + H2O(g) <—> C2H5OH (g)
Suggest how the process is managed to keep the waste of ethene to a minimum.

Answer 17

The unreacted ethene and steam can be recycled and reintroduced into the reactor to continue producing ethanol.

Question 18

Describe the trends that you would expect for 3 properties of the alcohols as the molecules increase in size. Enthalpy change of combustion must not be one of the properties you choose. [2]

Answer 18

Boiling point of alcohols increases
Solubility of alcohols decreases
Density of alcohols increases
Flammability of alcohols decreases
Viscosity of alcohols increases

Question 19

Give a reason why poly(ethene) is a better choice than tin for lining iron food cans. [1]

Answer 19

Poly(ethene) will not react with water or acids which the iron food can may contain, unlike tin.

Question 20

Poly(ethene) is a macromolecule made by addition polymerisation. Explain the terms macromolecule and addition polymerisation [3]

Answer 20

Macromolecule: a large molecule formed from many small molecules joined together

Addition polymerisation: a process where unsaturated monomers joined together covalently without losing any molecules or atoms to form addition polymers.

Question 21

Suggest, in terms of properties, why a polymer with more side chains has a lower world production than the other polymers [2]

Answer 21

Side chains in the polymer push the polymer chains away from each other, resulting in a polymer that is less strong and less hard. There is a lower production for such polymers due to a lower demand.

Question 22

Explain why and how HDPE has a different density from the other 2 polymers [2]

Answer 22

HDPE does not have any side chains resulting in a closer arrangement. This leads to a higher mass per unit volume. Therefore, HDPE has a higher density compared to other polymers.

Question 23

Name the uses of each compound. [3]
Bitumen, Sulfuric acid, ethene, ethyl ethanoate, calcium carbonate

Answer 23

Bitumen: for road surfaces
Sulfuric acid: to make detergents
Ethene: to make polymers for packaging
Ethyl ethanoate: as a solvent in inks
Calcium carbonate: for flue gas desulfurisation