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 (H3PO4) 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 with the general formula CnH(2n+1)OH, where n = 1,2,3 etc.

Question 3

Obtaining ethanol 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. They have a general formula of CnH(2n+1)COOH and are weak acids which dissociates partially in water to give a low concentration of H+ ions.

General formula:

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/reistant to corrosion by acid

Question 20

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

Answer 20

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

Question 21

Difference and similarities between addition polymers and condensation polymers

Answer 21

Difference
1. Monomers are UNSATURATED in AP but monomers of CP have 2 REACTIVE FUNCTIONAL GROUPS
2. Polymers of AP are formed with NO LOSS OF ATOMS OR SMALL MOLECULES but polymers of CP involves loss of small atoms or molecules
3. AP polymers have the SAME empirical formula as monomers but CP polymers have DIFFERENT empirical formulas as monomers
4. AP polymers are non-biodegradable but CP polymers are biodegradable
5. AP does not involve a change in mass but CP involves a change in mass.

Similarity:
Both involves a large number of small molecules joining together covalently to form a macromolecule.

Question 22

Suggest why vegetable oils are called tri -esters

Answer 22

They have 3 ester linkages.

Question 23

Explain why untreated oil containing acids affects rate of reaction

Answer 23

They react with the KOH catalyst hence rate of reaction with acids will be slower than rate of reaction without acids.

Question 24

State what happens to the ethanol when it reacts to acidified KMnO4 solution.

Answer 24

D undergoes oxidation to form a CARBOXYLIC ACID. ETHANOIC ACID is formed as byproduct.

Question 25

Which compound has the empirical formula calculated in ci?

Answer 25

B. B has a molecular formula of C2H4O2 and THUS THE RATIO C:H:O IN COMPOUND B IS 2:4:2 = 1:2:1 (Caps r what I missed it on)

Question 26

CuO reduced by reaction with methane to form Cu. Suggest 2 other products formed.

Answer 26

Steam/water CO2

Question 27

Explain the term macromolecule [1]

Answer 27

A long chain molecule made up of many small molecules known as monomers, joined together by covalent bonds through a process called polymerisation [1]

Question 28

Describe how impurities in ethanol produced from sugarcane is formed [2]

Answer 28

Ethanoic acid is formed from the oxidation of ethanol by atmospheric oxygen [1] Ethyl ethanoate is formed from the esterification reaction between ethanol and ethanoic acid. [1]

Question 29

Explain why some people think that ethanol is a ‘carbon neutral’ and renewable fuel and how the information shows that this is incorrect. [2]

Answer 29

People think that ethanol is a renewable fuel because it is derived from the fermentation of sugarcane, a crop that replenishes easily. During sugarcane growth, CO2 is absorbed during photosynthesis, offsetting the emissions produced when ethanol is burned as fuel. [1] However, transportation of sugarcane to process plants and the distillation process to obtain pure ethanol requires energy which is obtained from burning of fossil fuels. [1] these processes result in CO2 emissions, challenging fuel’s overall carbon neutrality.

Question 30

Discuss the differences and similarities between the structures of LDPE and LLDPE. [2]

Answer 30

S: both are made up of carbon and hydrogen atoms held together by strong covalent bonds and both have side chains. [1] D: LLDPE’s side chain is all the same (all -CH2 branched side chain) but LDPE’s side chain is all different and the side chains have different number of C atoms. [1]

Question 31

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

Answer 31

HDPE has no side chains and the polymers chains could be packed more closely [1], more polymer chain per unit volume, higher mass per unit volume thus denser than the other polymers. [1]

Question 32

Suggest, in terms of properties, why LDPE has a lower world production than the other polymers. [2]

Answer 32

Side chains in the polymer push the polymer chains away from each other. LDPE has more side chains so it is less strong and less hard than LLDPE and HDPE, making it less suitable to be used as building materials or packaging material [1]. It has a low softening temperature at 90dgC, making it less suitable to be used as hot drink containers or packaging for hot food. [1]

Question 33

Describe the pollution problems caused by the disposal of non-biodegradable plastics

Answer 33

Most plastics are non-biodegradable and cannot be broken down by bacteria and other microorganisms and decomposers. 1. Land pollution: burying plastic waste in landfills leads to increasing amount of built-up waste and takes up space 2. Water pollution: plastics endanger marine animals and may clog up rivers and drains, becoming breeding grounds for mosquitoes 3. Air pollution: plastics are mostly flammable, producing poisonous gas when incinerated

Question 34

Recycling of plastics

Answer 34

Plastic waste is washed, sorted to remove contaminants and shredded/grinded to smaller pieces before recycling. Physical method: melting small pieces of plastics, cooled and pulled into long thin strands and cut into pellets. Retains chemical composition of plastics. Chemical method: cracking to form short chains of alkanes to be used as fuels and alkenes to make useful chemicals. Depolymerisation breaks down polymers into their monomers and monomers can be converted to other useful chemicals.

Question 35

Depolymerisation

Answer 35

Process in which polymers are broken down into their monomers, diol and dicarboxylic acid, through Acid hydrolysis Condition: acid catalyst and water

Question 36

Describe the social, economic and environmental issues of recycling plastics

Answer 36

Env: wastewater generated from the recycling process not treated properly and discharged can contaminate water and cause water pollution Econ: 1. recycling plastics can be expensive due to cost of transportation, manpower, expensive machines to operate and large amount of energy from physical or chemical method of breaking down plastics 2. May not be economically viable to recycle plastics if the cost of recycling plastic waste is higher than the value of recycled plastics. Recycled plastics have a lower market value and sold at lower value than virgin plastics. Difficult for recycling businesses to survive if the cost of recycling plastic waste is too high. Social: more convenient to throw waste away and people are not aware of the proper way to recycle plastics.

Question 37

Describe a test that can be used to differentiate between organic compounds X and Y. [2]

Answer 37

Heat in (reflux) (✓) both compounds with aqueous acidified potassium manganate(VII) (✓). Purple solution decolourises with Y (✓) but not with X. 3(✓) – [2]; 1 – 2 (✓) – [1]

Question 38

Predict whether the dibromoalkane shown below forms an alkyne when it is added to potassium hydroxide solution. Explain your answer. [2]

Answer 38

It will not form an alkyne as the two bromine atoms are not on consecutive carbon atoms/ two carbon atoms that are side by side [1] unable to remove a Br2 molecule/ 2 bromine atoms [1] to form the C-C triple bond.

Question 39

Give one similarity and one difference between the condensation reaction of the formation of butyl ethanoate and the formation of Terylene. [2]

Answer 39

Similarity: Both reactions eliminate / release / produce water molecules / involve esther bond formation [1]. Difference: Ethyl pentanoate is a simple molecule but Terylene is a macromolecule / Terylene has more than one ester linkage but ethyl pentanoate has only one. [1]