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OCR A A-Level Chemistry > Chapter 13 - Alkenes > Flashcards

Chapter 13 - Alkenes Flashcards

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1
Q

What type of compound is limonene?

A

An alkene

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2
Q

What type of alkene is limonene?

A

Cyclic

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3
Q

What does limonene smell like?

A

Citrus fruits

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4
Q

What determines the colour of a flamingo?

A

The diet

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5
Q

What are alkanes?

A

Unsaturated hydrocarbons containing at least one C=C bond

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6
Q

General formula for alkenes

A

Cn H2n

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7
Q

What two bonds are found in a double bond?

A

Sigma and pi bonds

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8
Q

What is a sigma bond?

A

When two s orbitals overlap and create a region of high electron density between the two nuclei, forming a single covalent bond

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9
Q

How are sigma bonds formed?

A

When two s orbitals overlap

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10
Q

Why are sigma bonds so strong?

A

The high electron density between the two nuclei means that there is strong electrostatic attraction between the positively charged nuclei and the electron cloud

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11
Q

What is a pi bond?

A

A bond formed by the sideways overlap of two p orbitals. It has two parts to it - one above and one below the molecular axis

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12
Q

How is a pi bond formed?

A

Two p orbitals overlap sideways

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13
Q

Why are pi bonds much weaker than sigma bonds?

A

The electron density is spread out above and below the nuclei, so the electrostatic attraction is less

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14
Q

What do pi bonds do to a molecule?

A

They are rigid and hold the molecule in place around the two carbon atoms, meaning it can’t bend (unlike sigma bonds)

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15
Q

Why is the shape of the two atoms in a double bond trigonal planar 2

A

There are three regions of electrons

The three regions of electrons repel each other as much as possible, so the angle is 120

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16
Q

Where is maleic acid found?

A

Unriped fruit

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17
Q

Where is fumaric acid found?

A

Wild flowers

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18
Q

What are stereoisomers?

A

They have the same structural formulae but with a different arrangement of atoms

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19
Q

Where do E/Z isomers exist?

A

Molecules with C=C bonds

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20
Q

What two conditions are needed for there to be E/Z isomers?

A

A double carbon bond

Different groups attached to each carbon atom of the double bond

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21
Q

What is a Z isomer?

A

Both of the functional groups either below or above the double bond

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22
Q

What is an E isomer?

A

The same groups are positioned across the double bond

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23
Q

What conditions are needed for there to be cis-trans isomers?

A

A C=C bond
Each carbon in the double bond must be attached to 2 different group
One of the attached groups on carbon must be hydrogen

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24
Q

What is a cis isomer?

A

The groups are on the same side of the double bond

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25
Q

What is a trans isomer?

A

The groups are on opposite sides of the double bond

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26
Q

What does the Cahn-Ingold-Prelog rule state?

A

If the groups of high priority are on the same side of the C=C bond, it is a Z isomer
If the groups of high priority are on different sides of the C=C bond, it is an E isomer

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27
Q

How do we tell the priority of a group attached to a carbon?

A

Look at the Mr - the higher the Mr, the higher the priority

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28
Q

If two atoms attached to the carbon atoms have the same priority, what do you do then?

A

You find the group with the higher atomic number at the first point of difference

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29
Q

Why are alkanes much more reactive than alkanes?

A

The pi bond

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30
Q

Why does a pi bond make a compound more reactive?

A

The pi bond has a much lower bond enthalpy than the sigma bond and so breaks more easily

31
Q

What happens during an addition reaction with alkenes?

A

A small molecule is added to the C=C bond, causing it to break and form a new molecule

32
Q

What happens during an alkane hydrogenation reaction?

A

Hydrogen is added across the double bond. This forms an alkane

33
Q

What does vegetable oil contain?

A

Molecules with long, unsaturated hydrocarbon chains

34
Q

How is solid margarine formed?

A

Long, unsaturated chains of hydrocarbons are hydrogenated to form saturated chains. These have a lower melting point, so are more solid

35
Q

What are trans fats?

A

The pi bond is broken and reforms in the trans orientation

36
Q

What happens when alkanes are reacted with halogens?

A

The halogens are added across the double bond, forming dihaloalkanes

37
Q

How do you test for unsaturated alkenes?

A

Add bromine water to the solution. If it goes colourless, an alkene is present. If it stays orange, an alkane is present

38
Q

How is a haloalkane formed?

A

Reacting alkenes with gaseous hydrogen halides

39
Q

What is formed when alkenes react with steam with a catalyst (phosphoric acid)?

A

And alcohol as the steam ads across the double bonds

40
Q

When is the hydration of alkenes widely used in industry?

A

When producing ethanol from ethene

41
Q

What is electrophilic addition?

A

An addition reaction in which the first step is attack by an electrophile on a region of high electron density

42
Q

What happens during electrophilic addition?

A
  • double bond in alkenes represents a region of high electron density due to pi-electrons
  • Which attracts electrophiles
43
Q

What is the an electrophile?

A

An atom or group of atoms that is attracted to an electron – which centre and accepts an electron pair.

Usually a positive ion/partially positive (Delta) charge

44
Q

What is Markownikoff’s rule?

A

When a hydrogen halide reacts with an unsymmetrical alkenes where the hydrogen attaches to the carbon atom which has a greater number of hydrogen atoms and smaller number of carbon atoms

45
Q

What is a carbocation?

A

An ion that contains a positively charged carbon atom

46
Q

What is formed in the first step of electrophilic addition?

A

Carbocation

47
Q

What makes a carbocation stable?

A

The electron-donating ability of alkyl groups where each alkyl group donates and pushes electrons towards the positive charge of the carbocation. The charge is spread equally over the alkyl group.

The more alkyl groups attached to the positively charged carbon atom, the more charge is spread out, making the ion more stable

48
Q

What’s a polymer?

A

A large molecule formed from many thousands of repeated units of smaller molecules known as monomers

49
Q

What is additional polymerisation?

A

Formation of a very long molecular chain, by repeated addition reactions of many unsaturated alkenes molecules (monomers)

50
Q

What is the monomer?

A

A small molecule that combines with many of the monomers to form a polymer

51
Q

What’s a repeated unit?

A

A specific arrangement of atoms that occur in the structure over and over again

52
Q

Where is the repeated unit seen?

A

On the outside of brackets with the symbol n

53
Q

How is industrial polymerisations carried out?

A

At very high temperatures and high pressures using catalysts

54
Q

How is poly(ethene) made?

A

Heating a large number of ethene monomers at high pressure

55
Q

What objects are made out of poly(ethene)?

A

Supermarket bags/shampoo bottles/children’s toys

56
Q

What can poly(chloroethene) be prepared to make?

A

A polymer which is flexible/rigid

57
Q

What are the usages for ply(chloroethene)?

A

Pipes/flooring/fabric treatment/installation/cable sheathing

58
Q

What can a poly(propane) be used for?

A

Children’s toys/packing crates/guttering

59
Q

What can poly(styrene) be used for?

A

Packaging material/food trays/cups

60
Q

What is poly(tetrafluoroethene) be used for?

A

Non-stick pans/shoes/cable insulation

61
Q

Why is polymers having a lack of reactivity good?

A

For storing food and chemicals safely

62
Q

What is bad about polymers?

A

Most are nonbiodegradable hence killing marine life

63
Q

How can polymers be recycled?

A

Dance polymers are sorted, they can be chopped into flakes and washed, dried and melted. These polymers are cut into pellets in use by manufacturers making new products

64
Q

Why is your recycling PVC hazardous?

A

High chlorine contents therefore when burning PVC releases hydrogen chloride which is a corrosive gas

65
Q

Why can use waste polymers as fuel?

A

They have a high stored energy calue which when incinerated produces heat, generating steam to drive a turbine producing electricity

66
Q

What is feedstock recycling?

A

Chemical and thermal processes that can reclaim monomers, gases or oil from waste polymers

67
Q

What can be done with the materials produced from foodstoke recycling?

A

Can be used as raw materials for production of new polymers

68
Q

What is the advantage of food stock recycling?

A

Is able to handle unsorted and unwashed polymers

69
Q

How are bioplastics produced?

A

From plants starch, Celulose, plan oils and proteins

70
Q

What is good about bioplastics?

A

Protects the environment/conserve valuable oil reserves

71
Q

How are biodegradable polymers broken down?

A

By microorganisms in water, carbon dioxide, and biological compounds

72
Q

What up biodegradable polymers made out of?

A

Starch, cellulose

73
Q

What is good about, possible polymers?

A

They degrade and leave no visible or toxic residues

OCR A A-Level Chemistry (28 decks)

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