Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Chemistry > Alkenes > Flashcards

Alkenes Flashcards

1
Q

What do curly arrows represent?

A

The movement of electrons

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

What does the double bond of alkenes have?

A

A high electron density

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

What happens due to the high electron density of carbon carbon double bonds in alkenes?

A

Makes the bond more susceptible to attack by electrophiles

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

What are electrophiles?

A

Electron loving species

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

What is electrophilic addition?

A

The addition of an electrophile to a double bond

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

What does electrophilic addition include?

A

Hydrogen (hydrogenation reaction)
Steam
Hydrogen halide
Halogens

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

Which catalyst does hydrogenation use and what does it produce?

A

A nickel or platinum catalyst and it produces an alkane
Occurs under heat

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

What catalyst does reaction with steam use and what does it produce?

A

Phosphoric acid catalyst and it produces an alcohol
Occurs under heat

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

What do electrophilic additions with hydrogen halides and halogens produce and what conditions do they occur under?

A

Halogenoalkanes
Happens at room temperature

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

What is hydrogenisation extensively used for in industry?

A

To manufacture margarine

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

How is margarine produced?

A
  • Naturally occurring vegetable oils are unsaturated
  • Reacted with H2 and become C-C
  • Process changes properties of vegetable oils and converts it to solid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What can alkenes be oxidised and acidified by?

A

Potassium Manganate (VII) (KMnO4) - very powerful oxidising agent

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

What happens when alkenes are shaken with cold, dilute KMnO4)?

A

Pale purple solution turns colourless and product is a diol ( colour change can be used to distinguish between alkenes and alkanes as alkanes don’t change colour)

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

How can we think of the reaction between an alkene and an oxidising agent?

A

As an oxidation reaction followed by an addition

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

What are the steps in reacting an alkene with oxidising agent?

A
  • Potassium manganate solution provides an oxygen atom
  • Water in solution provides another oxygen and 2 hydrogen atoms, so addition of 2 OH groups across the double bond
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is heterolytic fission?

A

Breaking a covalent bond so that the more electronegative atom takes both the electrons from the bond to form a negative ion and leave behind a positive ion

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

What is the charge of hydrogen halides?

A

They are polar
e.g. HBr = H is positive, Br is negative

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

Which atom in HBr would be the electrophile?

A

H as it is electron deficient

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

What happens in an addition reaction of an alkene and a hydrogen halide?

A

The H atom acts as an electrophile and accepts a pair of electrons from the C=C in the alkene

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

What happens to the H-Br bond during electrophilic addition?

A

Breaks heterolytically, forming a Br- ion

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

What happens after the H has received the electron pair from the C=C in electrophilic addition?

A

Results in formation of a highly reactive carbocation intermediate which reacts with the Br- (nucleophile), to form halogenoalkanes

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

What is the charge of halogen molecules?

A

Non-polar

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

What happens when a Br molecule gets closer to the double bond of an alkene?

A

The high electron density in the double bond repels the electron pair in the Br-Br away from the closest Br atom

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

What happens in terms of charge on each Br atom as it gets closer to the C=C in an alkene?

A

Br closest becomes an electrophile and Br furthest away gets a negative charge (there is an induced dipole)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What happens in the addition reaction of a halogen with an alkene?
Closes Br atoms acts as an electrophile and accepts a pair of electrons from C=C (breaks heterolytically, forming Br- ion)
26
What is formed in the addition reaction of a halogen with an alkene?
Results in formation of a highly reactive carbocation intermediate which reacts with Br- to form a halogenoalkane
27
What is the general formula for cycloalkenes?
CnH2n-2
28
How does the double bond in an alkene affect its name?
Wherever the double bond is, you add that in the name e.g. double bond on carbon 2 in pentene - would be called pent-2-ene
29
What 2 types of bonding are there in the double bond of an alkene?
Sigma and pi
30
How does a sigma bond form?
One sp2 orbitals from each C overlap to form a single C-C bond
31
Can rotation occur around a sigma bond?
Yes
32
How does a pi bond form?
By the sideways overlap of 2 p orbitals on each C atom forming a pi bond above and below the plane of molecule
33
Can rotation occur around a pi bond?
There is restricted rotation
34
Is the sigma bond or pi bond stronger?
Sigma
35
Are pi bonds exposed and if so what does this mean?
Yes - they have a high electron density
36
What is caused by the fact that pi bonds have high electron densities?
They are vulnerable to attack by electrophiles
37
What can be used to test if a molecule is unsaturated?
Halogens
38
What is the halogen most commonly used for saturation tests?
Bromine water
39
How do you test if a compound is unsaturated?
Shake it with bromine water
40
What will happen when an unsaturated compound reacts with bromine water?
An addition reaction will take place and the solution will decolourise
41
What is addition polymerisation?
It is the reaction in which many monomers containing at least one C=C form long chains
42
What are the products of addition polymerisation?
Only the polymer
43
Which bond breaks in addition polymerisation?
The pi bond in each C-C
44
What happens after the pi bond breaks in addition polymerisation?
The monomers link together to form new C-C bonds
45
What is a polymer?
A long chain molecule that is made up of many repeating units
46
What can a polymerisation molecule be reprsented by?
The general formula or the displayed formula
47
What is a repeat unit?
The smallest group of atoms that when connected one after the other, make up the polymer chain
48
What do polymers provide for everyday use?
A readily available cheap alternative to many metal, glass, paper and cardboard materials
49
What makes polymers unreactive?
They are saturated and usually non-polar
50
What does the low reactivity of polymers make them useful for?
Certain uses e.g. food packaging
51
What is the bad aspect of polymers having a low reactivity?
Many of them are non-biodegradable
52
How do polymers affect sealife?
Waste plastic kills marine animals
53
What is one method of polymer disposal?
Use of landfill sites
54
What does polymer recycling do?
Reduces amount of waste going to landfill - newer landill sites have points where new waste is brought before going into actual landfill
55
What can recycling of polymers reduce the use of?
Finite resources (given that many polymers are made from products of cracking crude oil)
56
Why is recycling polymers a time-consuming process?
They have to be sorted into the different categories
57
What happens after polymers are sorted in recycling?
They are chopped, washed, dried, melted and then cast into pellets ready for use
58
What happens if the polymers are mixed when trying to recycle them?
When they are processed, it is wasted as it produces an unusable mix of polymers
59
Why can certain polymers cause problems when recycling?
Due to their composition (e.g. PVC contains chlorine)
60
How are modern techniques overcoming the PVC problem when recycling polymers (also other polymers)?
By dissolving the polymer and precipitating out the recycled material
61
Which polymers are still difficult to recycle?
Petroleum/natural gas derived polymers
62
How else can we dispose of petroleum/natural gas derived polymers and why?
Since they have a large amount of energy stored within the polymer chains, they can be incinerated
63
What can the process of incineration be used for?
- Can use the enrgy to boil water - The water vapour used to turn turbines in a power station
64
Why does the process of incineration cause environmental pollution?
Carbon in polymer can be released as CO2, contributing to global warming
65
What are some toxic waste products produced from the combustion of PVC?
Hydrogen chloride and other chlorinated molecules
66
What is PVC?
Poly(chloroethene)
67
What is feedstock recycling?
Waste polymers are broken down, by chemical and thermal processes - into monomers, gases and oils
68
What are the products from feedstock recycling used for?
As the raw materials in the production of new polymers and other organic chemicals
69
What is the major benefit of feedstock recycling?
It works with unsorted and unwashed polymers
70
What will chemists use when designing a sustainable polymer manufacturing process?
Principles of green chemistry
71
What kind of chemicals will scientists aim to use?
Ones that are as safe and environmentally friendly as possible
72
What will scientists try and do with the amount of chemicals they use?
Reduce it, physically as well as actual number of chemicals
73
What will scientists use where possible in terms of chemicals?
Renewable feedstock chemicals
74
What will scientists try and do in terms of energy in reactions?
Reduce energy requirement as well as increase energy efficiency (has both environmental and financial bonus)
75
Will scientists consides the lifespan of the polymer?
Yes - to see if its suitable for use
76
What will scientists try to do to atom economy?
Improve it (and reduce amount of waste by products)
77
How have chemists designed ways to remove toxic waste products before they are emitted into the atmosphere?
The waste gases from the incinerator are scrubbed or reacted with a base or carbonate
78
Why are waste gases scrubbed or reacted with bases or carbonates?
These neutralise the acids e.g. Calcium oxide neutralises HCl
79
Can biodegradable polymers be broken down?
Yes - over time by microorganisms
80
What are common products of the breakdown of biodegradable polymers?
CO2, water and other organic compounds
81
Which polymers are considered to be biodegradable and why?
Polyester and polyamide condensation polymers - can be broken down using hydrolysis (major advantage over products produced using alkene monomers)
82
What happens when polyester and polyamide condensation polymers are taken to landfill sites?
Broken down more easily so products used for other applications
83
What are compostable polymers made of?
Commonly plant based
84
What is being used in the production of biodegradable bin liners?
Plant starch
85
How do compostable polymers biodegrade?
Naturally - leaves no harmful residue

Chemistry (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions