Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OCR A a-level chemistry > Module 4 - [ch12,13] (alkanes alkenes) > Flashcards

Module 4 - [ch12,13] (alkanes alkenes) Flashcards

alkanes alkenes

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what are alkanes

A

crude oil
among the most stable organic compounds
unreactive
used as fuels
saturated hydrocarbons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what does the bonding look like in alkanes

A

saturated hydrocarbons
only single covalent bonds
each carbon makes 4 bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the shape of alkanes

A

each carbon atom is surrounded by 4 bonded pairs
tetrahedral
109.5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is meant by the term fractional distillation? [1]

A

separation by (differences in) boiling point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

why does boiling point of alkanes increase with chain length

A

as chain length increases, molecules have larger surface area
more surface contact possible between molecules
london forces between molecules are greater so more energy is required to overcome these forces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the effect of branching on boiling point of alkanes

A

branched isomers have lower boiling points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are the reasons for the lack of reactivity of alkanes

A

C - C C - H
sigma bonds are strong
C - C are non-polar
barely any difference in electronegativity of C and H so can also be described as non-polar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

combustion of alkanes

A

alkane + oxygen -> carbon dioxide + water

gives out heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

incomplete combustion of alkanes

A

limited supply of oxygen
toxic gases such a carbon monoxide (CO)
soot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

when do alkanes react with halogens

A

in the presence of sunlight
UV radiation provides initial energy for reaction to take place
substitution reaction
methane + bromine -> bromomethane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

mechanism from bromination of alkanes

A

initiation
Br - Br -> Br. + Br.
homolytic fission

propagation
CH4 + Br. -> CH3. + HBr
CH3. + Br2 -> CH3Br + Br.

termination
Br. + Br. -> Br2
CH3 + CH3 -> C2H6
CH3. + Br. -> CH3Br

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the limitations to radical substitution

A

further substitution
substitution at different positions on the carbon chain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are alkenes

A

unsaturated hydrocarbons
contain a C=C double bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how is a pi bond formed

A

overlap of adjacent p-orbitals below and above the Carbon atoms
can only be made after a sigma bond is formed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

describe the shape around a double bond

A

three regions of electron density around each carbon atom
trigonal planar
120

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are stereoisomers

what are the two types

A

they have the same structural formula but different arrangement of the atoms in space

EZ isomerism (only in compounds with C=C)
optical isomerism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are the conditions for EZ isomerism

A

. C=C double bond
. different groups attached to each carbon atom of the double bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is cis-trans isomerism

A

a special case of EZ isomerism
where one of the attached groups on each carbon atom of the double bond must be the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how do you assign priority

A

examine the atom directly attached to the carbon atoms of the double atom
greater atomic number = higher priority
if there is no difference, continue down chains till point of difference and compare those atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

cahn-ingold

A

if highest priority groups are on the same side
(Z)
on opposite sides
(E)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

why are alkenes more reactive than alkanes

A

the pi-bond
it is outside of the double bond, therefore more exposed
a pi bond readily breaks and alkenes undergo addition reactions easily

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

hydrogenation of alkenes

A

alkene + H2 -> alkane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

halogenation of alkenes

A

alkene + halogen -> something

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how do you test for an alkene

A

bromine water tests for unsaturation (the double bond)
orange -> colourless

25
Q

alkene + hydrogen halide

A

haloalkanes

26
Q

hydration of alkenes

A

alkene + water -> alcohol

27
Q

what does the double bond in an alkene represent

A

a region of high electron density
because of the presence of the pi-electrons
this high electron density attracts electrophiles

28
Q

what is the mechanism for the addition of a hydrogen halide

A

Hydrogen halide is polar
has dipoles
positive dipole attracted to double bond (high electron density)
double bond break open and H-Br bond also broken by heterolytic fission, electron pair goes to bromine atom
bromide ion and carbocation formed
carbocation has a positively charged carbon atom which attracts the ion
product formed!

29
Q

what makes the mechanism of the electrophile addition of Br2 different to the addition of HBr

A

Br2 is non-polar
when it approaches the double bond
pi-electrons interact with the electrons in the Br2
induced dipole

30
Q

What is Markovnikoff’s rule

A

when a hydrogen halide reacts with an unsymmetrical alkene the hydrogen attaches itself to the carbon with the greater number of hydrogen atoms and least carbon atoms

31
Q

carbocation stability

A

number of ‘alkyl’ groups attached to the positively charged carbon, more alkyl groups -> more stable
(how many carbons are attached to it)
primary carbocations are the least stable, tertiary the most

32
Q

why are tertiary carbocations the most stable

A

more alkyl groups
the charge is more spread out
making the ion more stable

33
Q

what are polymers

A

extremely large molecules made up from repeating units called monomers

34
Q

why am i waffling about polymerisation in this topic

A

alkene molecules undergo addition polymerisation
open the double bond
square brackets
slap an ‘n’ at the bottom right corner
!polymer!

35
Q

uses of polyethene

A

most commonly used polymers
supermarket bags
toys
shampoo bottles

36
Q

uses of polychloroethene

A

PVC
pipes, flooring, bottles, insulation

37
Q

polytetrafluoroethene (teflon)

A

coating non-stick pans
permeable membrane for clothing

38
Q

polystyrene (polyphenylethene)

A

packaging material
thermally insulating

39
Q

environmental concerns regarding polymers

A

disposal -> non-biodegradable

recycling PVC
hazardous due to high chlorine content
when burnt releases hydrogen chloride - a corrosive gas

feedstock recycling - reclaiming monomers from waste polymers

40
Q

bioplastics

A

produced from plant starch, cellulose

41
Q

biodegradable polymers

A

broken down by microorganisms into water, cO2 and biological compounds
compostable polymers

42
Q

photodegradable polymers

A

weakened by absorbing light

43
Q

what are the conditions for halogenation of alkenes

A

rapid addition reaction
room temp
addition reaction

44
Q

what are the conditions for hydrogenation of alkenes

A

nickel catalyst 150 degrees, 423K
addition reaction
double bond breaks, addition of hydrogen

45
Q

what are the conditions for hydration of alkenes

A

alkenes react with steam (H2O)
presences of phosphoric acid catalyst (H3PO4)
addition reaction

46
Q

electrophilic addition
alkene + hydrogen halide
what are the conditions

A

room temp
addition reaction
(bubbles through if the alkene is liquid)

47
Q

are alkane bonds polar

A

no
carbon and hydrogen have similar electronegativites

48
Q

describe the sigma bond in an alkane

A

covalent bond
direct overlap of s-orbitals

49
Q

what type of intermolecular force do alkanes have and why

A

london forces
because bonds are non-polar

50
Q

are alkanes soluble in water
why?

A

insoluble
hydrogen bonds in water are stronger than the london forces in the alkane
no polar bonds, so no attraction between water and alkane molecules

51
Q

what reactions will alkanes undergo

A

combustion
reaction with halogens

52
Q

what is the colour of the flame on a bunsen burner during complete combustion

A

blue

53
Q

how are halogenoalkanes formed from alkanes

A

radical substitution

54
Q

what intermolecular forces do alkenes have and why

A

london forces
non-polar bonds

55
Q

what will major products be formed from

A

the most stable carbocation
tertiary

56
Q

what are 5 ways in which plastic is disposed of

A

landfill
combustion
organic feedstock
recycling
reuse

57
Q

what is organic feedstock

A

plastics are separated and broken down into small organic molecules

58
Q

Outline two ways that waste polymers are processed usefully, rather than just dumped
in landfill sites [2]

A

combustion for energy generation
feedstock for chemicals, or plastics

59
Q

why do branched alkanes have lower boiling points

A

have fewer surface points of contact between molecules
weaker london forces
branches mean the molecules can’t get close together
decreasing intermolecular forces

OCR A a-level chemistry (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions