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A-Level Chemistry > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What is an alkene?

A

An unsaturated hydrocarbon

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2
Q

What is a hydrocarbon?

A

A compound that contains only carbon and hydrogen

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3
Q

What is an unsaturated compound?

A

A compound that contains double bonds

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4
Q

What is the general formula for alkenes?

A

CnH2n

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5
Q

What type of isomerism can alkenes exhibit?

A

Geometric isomerism

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6
Q

What are stereoisomers?

A

Isomers that have the same molecular formulae but a different spatial arrangement of atoms

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7
Q

Why do alkenes exhibit geometric isomerism?

A

There is restricted rotation around the double bond

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8
Q

When does geometric isomerism arise?

A

it arises when:

  • there is restricted rotation around the double bond
  • there are two different groups atoms attached at both ends of the double bond
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9
Q

What is an electrophile?

A

A lone pair acceptor

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10
Q

What is an addition reaction?

A

A reaction where a molecule joins to an unsaturated molecule to form a saturated molecule

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11
Q

What is carbocation?

A

A positive ion with the positive charge on a carbon atom

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12
Q

Why are alkenes reactive?

A

There is a high electron density in the double bond

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13
Q

What types of bonds are in double covalent bond?

A

Pi and Sigma bonds

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14
Q

Why Pi bonds vulnerable to attack by electrophiles?

A

They are exposed and have a high electron density

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15
Q

What is an electrophile?

A

A lone pair acceptor

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16
Q

What can be used to test for unsaturation?

A

Bromine water

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17
Q

What happens when a solution is made containing an alkene and bromine water?

A

The solution decolourises

Orange to colourless

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18
Q

Why does bromine water decolourise the solution?

A

The Br atom is added onto the double bond by electrophilic addition

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19
Q

What is formed when alkenes react with hydrogen halide?

A

Halogenalkanes

20
Q

What happens when hydrogen halides are added onto unsymmetrical alkenes?

A

Two products are produced

Major and minor

21
Q

What determines the atom economy of each product formed?

A

The stability of the carbocation intermediate determines the atom economy of each product

22
Q

What is an alkyl?

A

Alkanes with a hydrogen removed

23
Q

What happens when there are more alkyl groups around a carbocation?

A

The carbocation becomes more stable because there are more alkyl groups feeding electrons towards the positive charge

24
Q

What is the stability of a primary carbocation?

A

Least stable

25
Q

What is the stability of a tertiary carbocation?

A

Most stable

26
Q

What is formed when alkenes react with cold, concentrated sulfuric acid?

A

Alkyl hydrogensulfates

27
Q

What is formed when water is added to the alkyl hydrogensulfate in warm conditions?

A

An alcohol is formed

28
Q

Alkyl hydrogensulfates are formed through what type of reaction?

A

Electrophilic addition

29
Q

An alcohol is formed through what type of reaction?

A

Hydrolysis

30
Q

What is hydrolysis reaction?

A

A reaction where a molecule is split by the addition of water

31
Q

What is the purpose of the sulfuric acid in the reaction?

A

It is a catalyst because it is regenerated

32
Q

What is a polymer?

A

A long chained molecule formed from lots of repeated molecules joined together

33
Q

What is a monomer?

A

A small molecule repeated many times making a polymer

34
Q

Give examples of polymers

A

DNA
Proteins
Synthetics

35
Q

What is an addition polymer?

A

A polymer made from alkenes when they act as monomers because their double bonds open up joining together to long chains

36
Q

What are the properties of polyalkanes?

A

Unreactive
Non-polar
Saturated

37
Q

Why are polyalkanes unreactive?

A

The C-C and C-H bonds are strong

38
Q

What are the properties of long,straight chains?

A

Rigid

Strong

39
Q

What are the properties of short, branched chains?

A

Flexible

Weak

40
Q

What happens as the length of the chains increases?

A

The longer the polymer chains, the closer together they can get and the stronger the van der Waals forces between the chains

41
Q

How can polymers be modified?

A

They can be modified using plasticisers which makes them more flexible

42
Q

How do plasticisers make polymers more flexible?

A

The plasticiser molecules get between the polymer chains and push them apart
The intermolecular forces between the chains weaken
Therefore, the chains slide more making the polymer easy to bend

43
Q

What is PVC formed from?

A

Chloroethene

44
Q

What are the properties of rigid PVC?

A

Long, closely packed polymer chains
Hard
Brittle

45
Q

What is rigid PVC be used for?

A

Drainpipes

Window frames

46
Q

What are the properties of plasticised PVC?

A

Flexible compared to rigid PVC

47
Q

What is plasticised PVC used for?

A

Electrical cable insulation
Flooring tiles
Clothing

A-Level Chemistry (30 decks)

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