MOD 7

Question 1

How are most hydrocarbons obtained?

Answer 1

Currently, most hydrocarbons are obtained from either crude oil or natural gas via traditional drilling and pumping techniques.
These pumps may be present on land or in oceans as oil rigs
Crude oil is extracted and then refined via fractional distillation to produce many useful compounds, Crude oil is a mixture of hydrocarbon molecules that are mostly members of the homologous series of alkanes

Question 2

What are the environmental implications of obtaining and using hydrocarbons from the Earth?

Answer 2

• Crude oil and natural gas are non-renewable and finite resources, thus we are depleting Earth’s natural resources, decreasing sustainability for the future
• The mining and shipping of fossil fuels have led to oil spills that can occur during the transportation of fossil fuels, these are catastrophic and lead to deaths
• Combustion of hydrocarbons releases CO2 which is a greenhouse gas and accelerates global warming
• Global warming leads to the melting of polar ice caps destroying habitats of Antarctica species & causing rising sea levels
• release of oxides of nitrogen (NOX) and (SOX) when combusted in air leads to acid rain and smog

Question 3

What are the economic implications of obtaining and using hydrocarbons from the Earth?

Answer 3

• The petrochemical industry has created many jobs in many industries and improved our economies significantly to the extent that the stability of said economy relies heavily on this industry
• However, when accidents such as oil spills do happen, many jobs are lost and tourism suffers a great loss due to the non-aesthetic appeal of smog.

Question 4

What are the social implications of obtaining and using hydrocarbons from the Earth?

Answer 4

• Petrochemicals are the starting materials of many plastics, fuels and other essentials. Plastics are central to storage (lunch boxes, cartons) and are convenient for transporting food and other goods
• Fuels have allowed for mass industrialisation and factories producing the output necessary to allow the economy to run smoothly
• The state of the economy is linked to the standard of living, which has improved due to the use of hydrocarbons
• Cars, planes and boats are powered by fuels originating from hydrocarbons
  HARMFUL IMPLICATIONS:
• The bleaching of the Great Barrier Reef
• Corrosion of limestone buildings and structures
• Health issues from smog

Question 5

What is hydrogenation for alkene and alkyne, and what are the conditions required

Answer 5

Alkenes react with hydrogen to form alkanes, in the presence of a metal catalyst such as nickel, platinum, palladium or rhodium.
Alkynes react with hydrogen to form alkenes. To prevent the conversion of the alkene into an alkane, a Lindlar catalyst is used.

Question 6

What is halogenation for alkene and alkyne and what are the conditions required

Answer 6

By the same mechanism of an addition reaction, diatomic halogen molecules such as bromine (Br2) or chlorine (Cl2) may react with alkenes and alkynes to form haloalkanes.
No catalysts are required due to the relatively high reactivity.
Alkenes + halogens -> dihaloalkanes, same for alkynes.

Question 7

What is hydrohalogenation for alkene and alkyne and what are the conditions required

Answer 7

The addition of a hydrogen halide to an alkene produces a haloalkane.
Similarly, no catalysts are required.
The addition of a hydrogen halide to an alkyne produces a haloalkene
Note: 2 possible products

Question 8

What is hydration for alkene and alkyne and what are the conditions required

Answer 8

An alkene reacts with water to form an alkanol, distinguished by the hydroxyl (-OH) group. A dilute sulfuric acid or dilute phosphoric acid catalyst, as well as a temperature of 300C is required.
The hydration of alkynes produces a ketone in all instances except the hydration of ethyne (no terminal carbons) in which case an aldehyde, ethanal is formed. A mercury (II) compound like HgSO4 AND sulfuric acid are required to catalyse this reaction.

Question 9

Alkanes can undergo substitution reaction, What is the general reaction with a halogen?

Answer 9

alkane + halogen -> haloalkane + hydrogen halide

Question 10

How can alcohol be produced via hydration?

Answer 10

An alkene reacts with water to form an alkanol, distinguished by the hydroxyl (OH) group. A dilute sulfuric acid or dilute phosphoric acid catalyst is required. As well as a temperature of 300C is required. For the hydration of prop-1-ene, note there are two possible products propan-1-ol and propan-2-ol

Question 11

How can alcohol be produced via the substitution of haloalkanes?

Answer 11

The reaction between a haloalkane and water yields an alcohol by way of a substitution reaction. haloalkane + H2O -> alcohol + hydrogen halide with NaOH(aq) + heat required.

Question 12

How can alcohol be produced via fermentation?

Answer 12

Fermentation is the process of converting simple sugars like glucose into ethanol in an anaerobic environment with the aid of an alcohol-tolerant yeast.
The yeast produces enzymes that convert sugars into ethanol and CO2,
glucose -> ethanol + CO2

Question 13

What are the conditions required for fermentation?

Answer 13

• Alcohol-tolerant yeast: The organism must be able to undergo anaerobic respiration and tolerate alcohol up to a certain concentration
• Solution of carbohydrates such as glucose which are the nutrients required for cellular respiration of the yeast
• Anaerobic conditions: oxygen must be excluded to allow for anaerobic respiration of yeast. In the presence of oxygen, ethanal and ethanoic acid are produced instead.
• 30 degrees which is the optimum biologically active temperature. At temperatures higher or lower than these, enzymes in yeast may be denatured or inactivated respectively.
• Water: provides an aqueous environment for reaction to occur
• Mildly acidic conditions are desired to prevent the growth of pathogens

Question 14

Alcohols undergo dehydration to form what

Answer 14

Alkenes and water molecule, in the presence of concentrated sulfuric acid (H2SO4)

Question 15

Alcohols undergo substitution with hydrogen halide to form

Answer 15

haloalkane + water

Question 16

primary alcohols oxidise in 2 stages, in the presence of potassium permanganate these are

Answer 16

primary alcohol -> aldehyde -> carboxylic acid

Question 17

secondary alcohols oxidise in 1 stage in the presence of potassium permanganate, which is

Answer 17

secondary alcohol -> ketone

Question 18

How do you prepare an ester?

Answer 18

Under reflux conditions, which involves heating the chemical reaction for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser. The vapours produced above the reaction continually undergo condensation, returning to the flask as a condensate. Preventing the loss of reagent. In addition, a heating mantle is used rather than a bunsen burner for more even heating (safer) for the flammable reagents. Heating, along with the sulfuric acid catalyst, increases the RR, as ester formation is very slow in nature. The sulfuric acid catalyst is concentrated as it is meant to act as a dehydrating agent, as water is produced in this reaction. When choosing reagents, methanol and ethanoic acid are ideal as they are non-toxic and readily available.

Question 19

How do you purify an ester?

Answer 19

After reflux has been performed (-30 mins), a mixture of organic and inorganic reagents as well as the catalyst will be in the round bottom flask
1. Water is added to dissolve any inorganic substances (e.g. catalyst), and a separating funnel is used to separate the immiscible liquids of different densities into different layers
These layers could look like:
Organic layer: ester, leftover alcohol and/or carboxylic acid
Aqueous layer: Water is denser and will be on the bottom with
the inorganic substances dissolved, some of the alcohol and
carboxylic acid will be in the aqueous layer as not all of it will
dissolve.
2. The use of three beakers to separate the layers using a separating funnel.
3. Once the organic layer is obtained in a separate beaker, sodium carbonate is added to remove any carboxylic acid by producing a carboxylate ion and CO2
- The gas escapes by bubbling
- The carboxylate ion is soluble in water (ion-dipole forces)
4. Water is added to dissolve the carboxylate ion and then the separating funnel is used again to get a clean organic layer.
5. Fractional distillation allows the ester to be separated from the alcohol, due to a small difference in BP.
This produces a final PURE ESTER.

Question 20

Explain how a surfactant washes away grease (non-polar)

Answer 20

1. The hydrophobic tail (non-polar) is able to go and bond with the grease (also nonpolar) molecules on the surface forming a monolayer
2. Agitating this solution, often by shaking or scrubbing, lifts this layer of grease off the surface, allowing the undersides to also interact with the surfactant molecules. Eventually, this forms a micelle.
3. The formation of micelles is called emulsification and this is an important step in the process as it allows these grease molecules to be efficiently washed away with water.

Question 21

Explain how a surfactant acts in water (polar)

Answer 21

At lower concentrations, a monolayer forms with the hydrophilic heads in the water and the hydrophobic tails facing out
At higher concentrations, the molecules may need to cluster together. The only way this is possible inside the depths of the water is in a spherical arrangement called a micelle. The hydrophilic heads face out towards the water whilst the hydrophobic tails are left to face inwards to minimise repulsion with the water.

Question 22

What are the properties and thus respective uses of LDPE?

Answer 22

The polymer is amorphous in structure. The chain branching prevents chains from packing well together giving rise to weaker dispersion forces and thus lower MP, soft and flexible.
USES: Cling wrap, plastic bags (i.e. flexible items)

Question 23

What are the properties and thus respective uses of HDPE?

Answer 23

Minimal chain branching means the polymer chains pack well together and thus experience extensive dispersion forces, giving rise to its properties of strong and rigid. And high melting point.
USES: Children’s toys, garbage bins and microwavable containers (due to high MP)

Question 24

Polyvinyl chloride is an example of an addition polymer, what are it’s properties and uses?

Answer 24

Whilst Bulky chlorine atoms prevent chain from packing well, C-Cl bonds are polar and the dipole-dipole forces make up for the lack of crystallinity and make it quite hard and durable. USE: Tool handle and water pipes.
When plasticisers (small molecules) are inserted between polymer chains, they hold the polymer chains further apart and weaken IMF between them. These make the polymer more flexible, hence allowing PVC’s USE: in credit cards and garden hoses.

Question 25

Polytetrafluoroethylene (TEFLON) is an addition polymer, what are its properties and uses?

Answer 25

C-F polar bands form strong dipole-dipole forces and thus the polymer is strong and durable. The extensive IMF between its own chain, mean it repels other molecule (both polar and non-polar) allowing Teflon’s use in non-stick pans and carpets to make them flame-resistant.

Question 26

Polystyrene is an addition polymer, what are its properties and uses?

Answer 26

The bulky phenyl side group makes packing more amorphous. There are no polar bonds, so only weak dispersion forces are present. Despite this, the bulky phenyl side groups resist chain flexing and make the polymer hard and brittle. When gas is added to the polymerising mixture, expanded polystyrene is formed. These have great insulating properties to heat as well as sound. They also have low density.
USES: disposable cutlery, CD cases, soundproofing, floatation devices

Question 27

What is an example of a condensation polymer?

Answer 27

Nylon is a polyamide formed by the linkage of monomers by amide links. The hydrogen bonds present make crystals of nylon very strong because they hold the nylon chains together very tightly. Nylon can be easily drawn into fibres that have a high tensile strength and are used to produce strong, lightweight materials. USES: clothes, parachutes, fishing line, guitar strings
(high tensile material)

Question 28

What are the safety hazards of esterification?

Answer 28

• Alcohols are flammable, so do not use open flames. A heating mantle should be used instead of a Bunsen burner.
• Liquid carboxylic acids are corrosive, so wear safety glasses to avoid contact with eyes.
• Concentrated sulfuric acid is corrosive, so only small quantities should be used, and safety glasses must be worn.

Question 29

State ONE safety concern associated with organic liquids and suggest ONE way to address this safety concern

Answer 29

Organic solvents are generally flammable so no sources of ignition should be present, or work in fume hood.

Question 30

Explain why certain polymers, are classed as polyesters and account, in terms of bonding, for their strength, durability and resistance to stretching

Answer 30

These compounds are called polyesters because they are produced from monomers that bond by forming ester linkages, by the reaction between the carboxyl group of a carboxylic acid and a hydroxyl group of an alcohol monomer. Polyesters are relatively strong plastics due to the ester groups present which are polar. so apart from dispersion forces, there are stronger dipole-dipole attractions between polymer chains. These extra forces not only increase strength but in the case of fibres and carpets, make them more resistant to wear, decreasing stretchability.