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Chemistry > DJA 5). Alkenes > Flashcards

DJA 5). Alkenes Flashcards

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1
Q

general formula of alkenes

A

CnH2n

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2
Q

whats special about alkenes

A

c=c (carbon-carbon double bond)

restricts rotation of groups attached (therefore E/Z isomers)

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3
Q

how many electrons does the c=c contain and what do we think of it as

A

4 electrons
electron dense
so has potential to attract d+ or positive ions
so is reactive

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4
Q

electrophiles are

A

species looking for a pair of electrons (eg H+)

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5
Q

induced dipole of Br2 by c=c

A

electron dense c=c ‘pushes’ electron density in Br2 from one side to another causing a temporary dipole

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6
Q

structure of the carbocation

A

positively charged ion. when the reaction is occurring the Br can attach onto carbon 1,2,3…..

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7
Q

primary secondary and tertiary structures

- how to identify

A

find the special bit (in our case the positive charge)
find the carbon it is related to
find how many carbons this carbon is attached to (1=primary, 2=secondary…)

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8
Q

primary secondary and tertiary structures

- which is least stable

A

primary

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9
Q

primary secondary and tertiary structures

- which is most stable

A

tertiary

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10
Q

electrophilic addition of H2SO4 to alkenes

  • type of reaction
  • what type of h2so4 is used
  • what can happen to the product
A
  • very exothermic
  • conc h2so4 is used
  • product can be converted into alcohol by addition of water (H2SO4 is reformed so has acted as a catalyst
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11
Q

test for c=c

A

add orange Br2 water –> decolourises

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12
Q

polymer defintion

A

large molecule made up of lots of repeating units called monomers

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13
Q

how to modify plastics

A

add plasticisers
they are small molecules that can get in between the chain of polymer, force them apart and allow them to slide over each other

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14
Q

poly(chloroethane) is also known as…

A

PVC

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15
Q

two types of poly(ethene)

A

LOPE

HOPE

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16
Q

when do you get LOPE poly(ethene)

A 
high pressure
high temperature
produces branch chain polymers which don't pack well
molecules are flexible
uses - plastic bags, electric cables
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17
Q

when do you get HOPE poly(ethene)

A

just over room temp and pressure
less branching so more closely packed
molecules are inflexible
uses - crates, bottles, buckets

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18
Q

environmental issues with poly(ethene)

A

made from crude oil thereofre non-renewable
inert as non-polar
non biodegradable
high melting point as strong vdw between molecules

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19
Q

alcohol functional group

A

O-H

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20
Q

two ways to produce ethanol

A

direct hydration

fermentation

21
Q

comparing direct hydration and fermentation

- rate of reaction

A

DH vs fermentation

fast vs slow

22
Q

comparing direct hydration and fermentation

- cost

A

DH vs fermentation

expensive vs cheap

23
Q

comparing direct hydration and fermentation

- manpower

A

DH vs fermentation

low vs high

24
Q

comparing direct hydration and fermentation

- purity

A

DH vs fermentation

pure vs impure

25
Q

comparing direct hydration and fermentation

- type of process

A

DH vs fermentation

continuous vs batch

26
Q

comparing direct hydration and fermentation

- environmental impact

A

DH vs fermentation

non-renewable (ethene from crude oil) vs renewable (sugar cane)

27
Q

direct hydration equation

A

h2c=ch2 + H2o ——–> h3c-ch2-o-h

H3PO4

28
Q

type of mechanism to make alcohol

A

electrophilic addition

see hard copy cards

29
Q

fermentation equation

A

c6h12o6 ——> 2c2h5oh +2co2

30
Q

conditions for fermentation

A

yeast
zymase
35 degrees
absence of air

31
Q

what alcohol content does fermentation produce and why

A

up to 15%, because any greater and yeast is killed

32
Q

what can fermentation alcohol be used for (other than to drink)

A

biofuel = renewable

33
Q

why are biofuels considered carbon neutral

plus equations

A

a carbon neutral substance takes in as much CO2 as it produces
+6 6CO2 + 6H2O —> C6H12O6 + 6O2 (photosynthesis)
+4 C6H12O6 —–> 2C2H5OH +2CO2 (fermentation)
+0 2x C2H5OH + 3O2 —> 2CO2 + 3H2O (fuel is burnt)

34
Q

why is considering biofuels as carbon neutral too simplistic

A

co2 will be released at many other points
extraction of glucose
fermentation (must heat to 35)
transporting raw materials

35
Q

oxidation of alcohols

- oxidising agent (what happens to the oxidising agent and what can we see)

A 
K2Cr2O7 /HCl
acidified potassium dichromate 
it gets reduced
species that gets reduced.... (K+ is a spectator ion)
Cr2O7^2-
orange

Cr^3+ green

36
Q

primary alcohol is oxidised…

A

twice

37
Q

primary –>….—>….

A

primary –>aldehyde—>carboxylic acid

38
Q

secondary –> …

A

secondary –>ketone

39
Q

tertiary–>…

A

not possible

no reaction

40
Q

to make an aldehyde we use which method

A

distillation

41
Q

to make a carboxylic acid we use which method

A

reflux

42
Q

why do we use different methods to collect aldehydes and carboxylic acids

A

carboxylic acid = hydrogen bonding = high bp
aldehyde = permanent dipole forces = lower bp
so have to re-condense the aldehyde to make a carboxylic acid

43
Q

testing for aldehydes and ketones

A

tollens reagent
aldehyde = silver mirror
ketone = NVC

44
Q

testing for alcohols

A

add a very small piece of sodium

if gently fizzes then alcohol, if violent, water or carboxylic acid

45
Q

another way to test for aldehydes (not tollens reagent)

A

Fehlings solution (blue) –> brick red precipitate

46
Q

haloalkane test

A

warm then add silver nitrate
white prcipitate - chloroalkane slowest
cream precipitate - bromoalkane
yellow precipitate - iodoalkane fastest

47
Q

carboxylic acid test

A

add sodium hydrogencarbonate

bubbles = carboxylic acid

48
Q

catalyst and conditions for dehydration of alcohols

A

Al2O3
600 degrees c
conc H2SO4

Chemistry (23 decks)

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