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Dr stead chem > Alkenes and alcohols in industry, and addition polymerisation > Flashcards

Alkenes and alcohols in industry, and addition polymerisation Flashcards

1
Q

What are the two ways that ethanol is produced?

A

-direct hydration
-fermentation

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2
Q

What is a continuous industrial process?

A

one in which more reactants are added as the products are removed

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3
Q

Why would we do a direct hydration?

A

alkenes undergo a direct hydration (an addition reaction) with water in the presence of an acid catalyst to form an alcohol

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4
Q

What are the reactions conditions for a direct hydration?

A

-steam
-300C
-65 atmospheres
-concentrated phosphoric acid catalyst (H3PO4)

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5
Q

What are the advantages of direct hydration?

A

-fast reaction
-high yield of ethanol
-pure ethanol
-continuous process cheap on manpower

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6
Q

What are the disadvantages of direct hydration?

A

-uses ethene which is a finite resource
-continuous process requires expensive equipment

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7
Q

Why is the pressure carefully controlled in direct hydration reactions?

A

very high pressures could result in a polymerisation reaction

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8
Q

What is fermentation and it’s reaction conditions?

A

-when an aqueous solution of plant sugar is converted into ethanol and CO2 by living yeast cells
-anaerobic conditions and 35C, as oxygen would oxidise the ethanol to a carboxylic acid

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9
Q

What are the advantages and disadvantages of fermentation?

A

-can’t be carried out at high temperatures as yeast can’t survive
-can’t be carried out at low temperatures as enzymes aren’t activated
-batch process producing a mixture of compounds

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10
Q

What are the reaction conditions for the dehydration of alcohols?

A

300C/65 atmospheres/concentrated phosphoric acid

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11
Q

Draw the mechanism of the direct hydration of ethene, and write the name and conditions

A

-by electrophilic addition
-300C
-concentrated H3PO4 acid catalyst
-steam
-6500kPa

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12
Q

When used on larger alkenes, how do you know which product will be the major product?

A

it will be whatever one is formed from the more stable carbocation (which one is connected to the highest number of other carbons directly)

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13
Q

What are polymers?

A

long chain molecules formed when a large number of monomers join together

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14
Q

Give an example, and uses of natural polymers

A

-DNA
-natural polymers have been used for many years to make things like fabrics

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15
Q

Give 2 examples of artificial polymers

A

-artificial silk
-hard rubber

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16
Q

What is addition polymerisation?

A

the reaction in which many monomers with at least 1 C=C bond form long chains of polymers as the only product

17
Q

What are addition polymers also sometimes called?

A

chain-growth polymers

18
Q

How do you name an addition polymer?

A

poly(alkene name)

19
Q

Why are addition polymers chemically unreactive and why is this a useful trait?

A

it has strong covalent bonds and no bond polarity, useful because it can’t be attacked by acids/alkalis/oxidising agents

20
Q

Draw the addition polymerisation general reaction

A

n CH3=CH3 —-> -(- CH2CH2-)- n [FULL STRUCTURAL FORMULA DRAWN]

21
Q

What mechanism are addition polymers usually formed by, and what are the common reaction conditions?

A

via a free radical mechanism, high pressure and a free radical initiator like an organic peroxide

22
Q

What happens when you make an addition polymer from an alkene that is bigger than an alkene?

A

there can only be the saturated c-c bonds on the horizontal skeleton, so the extra ones are added like methyl groups to the vertical lines
CH3 H
│ │
-c—–c-
│ │
H H

23
Q

Why do the properties change in polyalkene molecules?

A

-polyalkene molecules are usually non-polar so there are only weak van der Waals forces between the neighbouring molecules
-larger molecules have more electrons so have stronger van der Waals forces which increases the melting/boiling point
-if a molecule is not branched then the molecules can pack together more closely, (making the material stronger and more rigid) so have stronger van der Waals forces.
-if a molecule is branched then the molecules can’t pack as closely (making the material more flexible) so have weaker van der Waals forces

24
Q

When can a polyalkene molecule be polar?

A

when it contains electronegative atoms, like in poly(chloroethene)

25
Q

What is poly(ethene) used for?

A

making plastic bags and clingfilm

26
Q

What is poly(propene) used for?

A

making crates/pipes/chairs/car bumpers/made into fibres used in the backing for carpets/thermal clothing/crisp packets

27
Q

Why is poly(ethene) more difficult to recycle than poly(propene)?

A

it cannot as easily be collected, cleaned, and recycled so ends up in landfill, but poly(propene) is able to be collected-cleaned-cut up into small pieces-melted-remoulded

28
Q

What is poly(chloroethene) also known as?

A

PVC (polyvinylchloride)

29
Q

What type of intermolecular forces are present in PVC?

A

permanent dipole-dipole forces between the polymer chains due to the polar C-Cl bonds

30
Q

What are the properties of PVC and what is it used in?

A

hard but brittle, used to make drain pipes and window frames

31
Q

How can we make polymers more flexible?

A

by adding a plasticiser

32
Q

How do plasticisers make polymers more flexible?

A

-plasticiser molecules get between the polymer chains and push them apart
-this reduces the strength of the van der Waals forces between the chains so the chains can slide around more, making the molecule more flexible

33
Q

Why are polymers strong?

A

very large molecules so have lots of electrons so have stronger van der Waals forces that require a lot of energy to break

34
Q

What is the difference between the uses for PVC and plasticised PVC and why?

A

plasticised PVC is much more flexible than rigid PVC, it is used to make electrical cable insulation, flooring tiles, and clothing

35
Q

Why are polymers non-biodegradable?

A

as they are chemically inert (strong covalent bonds with no bond polarity)

36
Q

What is one proposed way of disposing of polymers?

A

polymers are highly flammable so you can incinerate them
benefits- the heat from incineration can be used to make steam to drive turbines which would generate electricity

negatives- incineration produces greenhouse gases and other toxic gases

37
Q

What are the cons of recycling polymers?

A

-expensive
-different types of plastics have to be separated from each other before being recycled

38
Q

What are the cons of recycling polymers?

A

-expensive
-different types of plastics have to be separated from each other before being recycled

Dr stead chem (20 decks)

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