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A Levels > 3-3: Alkenes And Alcohols > Flashcards

3-3: Alkenes And Alcohols Flashcards

(52 cards)

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1
Q

What property do carbon-carbon double bonds have?

A

High electron density

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2
Q

What are electrophiles?

A
  • ‘electron-loving’
    -(usually positive, e.g. ions or d+) electron pair acceptors
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3
Q

Explain the mechanism of an electrophilic addition reaction of an alkene with Br2

A
  • high electron density of C=C polarises the Br—Br bond
  • The two electrons from the C=C bond attack d+ Br atom,opening the C=C bond
  • The Br—Br bond breaks (d- takes bonding pair, -:Br) and one C forms a bond with 1 electron to Br+
  • second C is therefore left with a positive charge
  • carbocation intermediate
  • -:Br then attacks the carbocation, donating its lone pair to bond with Carbon 2
  • bromoalkane then formed
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4
Q

How does the electrophillic addition of an alkene differ with HBr compared with Br2?

A
  • Thw HBr bond is already polar, due to Br’s high electronegativity
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5
Q

Describe the electrophilic addition of ethene with H2SO4, what is produced and the one other reagent you keep forgetting?

A
  • heat ethene with water and conc H2SO4
  • electrophilic addition, C=C opens to bond to H d+ on H2SO4
  • carbocation intermediate
  • bond formed between next -:O and C+, ethyl hydrogen sulfate formed (CH3CH2OSO2OH)
  • then cold water is added and the product is warmed, causing hydrolysis.
  • OH group swapped for the OSO2OH group, forms alchohol
  • OSO2OH gains H+ from the water (in excess) and forms H2SO4 again.
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6
Q

Explain how bromine water can test for unsaturation (C=C)

A
  • shake alkene with orange bromine water
  • orange—> colourless
    electrophillic addition of Br across C=C to form a dibromoalkane
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7
Q

What must an alkene be if multiple possible products are to be able to form?

A

Asymmetrical

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8
Q

What does the amount of major and minor products formed depend on?

A
  • how stable the carbocation intermediate is
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9
Q

What are the three types of carbocation intermediate from least to most stable?

A

H
- primary: R-C-H
+
R
- secondary: R-C-H
+
R
- tertiary: R-C-R
+

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10
Q

Why does having more R groups make a carbocation intermediate more stable?
How can this be shown?

A

-The alkyl (R) groups feed electrons towards the positive charge
- an arrow on the bond stick from the R to the C

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11
Q

What is the major product in terms of stability?

A

The more stable product (more R groups)

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12
Q

What is the minor product in terms of stability?

A

The less stable product (fewer R groups)

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13
Q

What is a substituted alkene?

A

An alkene with hydrogen atoms replaced for other atoms or groups of atoms

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14
Q

What do we use artificial polymers for in everyday life?
How did polymers develop in the 20th century?
What are we constantly aiming to improve?

A
  • plastic bags
  • raincoats
  • non-stick pans
  • car tyres
  • nylon & Kevlar were developed
  • cost and function
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15
Q

What are polymers always made out of?

A

Alkenes and substituted alkenes

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16
Q

How are addition polymers formed?

A

The double bond in alkenes open up and join together to make long chains

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17
Q

How are addition polymers drawn?

A
  • double bond opens to single
  • monomer within brackets
  • extended outer bonds passing through brackets
  • n (no.repeating units)
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18
Q

How do you find the monomer from a displayed (formula) polymer?

A
  • It is the smallest possible repeating unit
  • replace the double bond
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19
Q

How are addition polymers named (IUPAC)?

A
  • Poly(IUPAC name of monomer)
  • if the name of the monomer has no number in it, no brackets are necessary
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20
Q

Explain the main property of polymers?
In genral how are they bonded?

A
  • very unreactive (strong, non-polar C-C/C-H bonds, no reactive function groups)
  • generally non-polar
  • saturated
  • strong covalent bonds
  • intermolecular forces between chains (often only van der waals)
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21
Q

What is the structure and properties (and why) and the uses of PVC?

Study These Flashcards
A
  • poly(chloroethene)
  • polar covalent bonds between Cl and C
  • permanent dipole forces between polymer chains (d+/d- between zigzag)
  • therefore hard but brittle
  • drain pipes and window frames
22
Q

How can the properties of PvC be modified using a plasticiser and what is it used for?

Study These Flashcards
A
  • plasticiser molecules get between polymer chains and push them apart
  • reduces IMF strength
  • chains slide around more
  • flexible
  • electrical cable insulation, flooring tiles, clothing
23
Q

What is the genral formula of an alchohol?

24
Q

What are primary alchohols?

Study These Flashcards
A
  • one R group bonded to the OH carbon
    H
  • R-C-OH
    H
  • 1*
25
What are secondary alchohols?
- two R groups bonded to the OH carbon R - R-C-OH H - 2*
26
What are tertiary alchohols?
- Three R groups bonded to the OH carbon R - R-C-OH R -3*
27
How are alkenes produced industrially? What are they used for?
- The dehydration of alchohols by acid-catalysed elimination reactions - produce polymers without using monomers derived from crude oil *alchohols can be produced through fermentation*
28
Describe the dehydration of ethanol with an acid-catalyst via elimination reaction
- lone pair on O (from OH on C) bonds to H+ (from H2SO4 acid) - this protonates the alchohol, giving O a +1 charge - this +1 pulls the electrons away from the C bond, breaking it - H2O leaves - carbocation intermediate - C+ attracts both electrons from H bond - H bond breaks and H+ is lost - C=C produced - ethene, water and H+ (H2SO4) formed
29
Why does the dehydration of longer, asymmetrical alchohols result in more than one product?
Because the the double bond can form on either side of the carbocation intermediate (where the Oh was)
30
Describe the first distillation in the purification of a mixture of products (What is added?)
- reaction - distillation with conc H2SO4 and H3PO4 (carborundum boiling chips) - gently heat to around lower bp, (83C bp of cyclohexene) - still somewhat impure
31
Describe the separation of stage of purification
- still somewhat impure after distillation - transfer to separating funnel - add water to dissolve soluble impurities - allow it to settle into layers - drain off aqueous layer (bottom) - (less) impure product left behind
32
Describe the final purification of the separation of a mixture of products
- drain off impure product (from separating funnel) into a round bottomed flask - add anhydrous CaCl2/MgSO4 (drying agents), stopper and swirl - 20 mins with occasional swirling - *may have to distil once more, only collect exact bp of desired product*
33
What are the 3 stages of purification of
- first distillation - separation (separating funnel) - purification (drying agent) - possible final distillation
34
What is the industrial method for the production of alchohols? What are the conditions required? What is the yield?
- the hydration of alkenes with steam and an acid catalyst - 300C - 60atm - 5% (but recycle I reacted alkene, so overall 95%)
35
Describe the mechanism for the industrial production of an alchohol from ethene (hydration of ethene)
- pair of electrons in C=C bonds to H+ (from acid catalyst) - carbocation intermediate - lone pair from H2O (steam) bonds to acid catalyst - H+ lost - ethanol + H+ formed
36
Describe the process of the fermentation of glucose to produce ethanol and CO2
- exothermic reaction in anaerobic conditions - optimal 30-40C for yeast - C6H12O6 (aq) (+ yeast)—>2C2H5OH(aq) + 2CO2(g) - yeast dies at 15% ethanol - renewable - fractional distillation to purify (costly)
37
What are the two different methods of producing ethanol? What kind of process is each in terms of batch and continuous?
- Hydration of ethene (continuous) - fermentation of glucose to produce (batch)
38
What are the pros and cons of the hydration of ethene to produce ethanol?
- very fast - pure product - from oil, finite resource - continuous, expensive equipment but low labour costs
39
What are the pros and cons of the fermentation of glucose to produce ethanol?
- very slow - very impure - renewable - batch production, cheap equipment but high labour costs
40
What is a biofuel? Give one examples
- A fuel made from biological material that has recently died. - ethanol from fermentation of suger cane
41
Justify the conditions required for the fermentation of glucose
- 30-40C (/PH): optimise the yeast enzymes, avoid denaturing - anaerobic: prevents aerobic respiration of yeast which would produce CO2 and water, not ethanol - yeast itself: contains catalysing enzymes for the production of ethanol
42
What are the advantages of using biofuels?
- renewable - carbon neutral (ish)
43
What are the disadvantages of using biofuels?
- food vs fuel (ppl go hungry) - deforestation- produces CO2 - fertilisers, pollute waterways, release nitrous oxide - our transport can run on high ethanol fuels - energy used in the transportation machinery and refining of biofuels
44
What are the 3 reactions showing how the production of ethanol via fermentation is carbon neutral
- (production of glucose from plant growth, 6 moles taken, 1 mole glucose) 6CO2 + H2O —> C6H12O6 + 6O2 - (fermentation, 2 moles CO2 released from 1 mole glucose) C6H12O6 —> 2C2H5OH + 2CO2 - (ethanol burned, ; moles released, 2 moles ethanol burned) 2C2H5OH + 6O2 —> 4CO2 + 6H2O - 6 moles taken in, 6 moles released
45
What oxidising agent is used to oxidise 1* and 2* alchohols? What happens to it over the reaction?
- acidified potassium dichromate - (K2Cr2O7) = Cr2O7^2- - it is reduced from the orange Cr2O7^2- to the green Cr^3+
46
What is the functional group of an aldehyde?
- C=O, always on carbon 1 O || - R-C-H (carbonyl group)
47
What is the functional group of an ketone?
- C=O, always on a middle carbon O || - R-C-R
48
What is the functional group of an carboxylic acid?
O || C—OH
49
What can primary alchohols be oxidised to and in what order? What are the conditions required for each?
- aldehyde: gently heated with potassium dichromate sol and sulfuric acid Distillation aparatus, don’t allow to over boil (Then) - carboxylic acid: excess [O] under reflux (no volatile solvents, reactants or products are lost)
50
What can secondary alchohols be oxidised to? What are the conditions required?
- ketone: reflux, acidified conditions
51
Can tertiary alchohols be oxidised with acidified potassium dichromate? How can they be?
- no - burning them
52
How can you distinguish between aldehydes and ketones?
- add Fehlings solution: aldehyde is oxidised, blue—> brick red precipitate - add tollens reagent: aldehyde is reduced to silver (mirror) - no change for either with ketones

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