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A-Level Chemistry > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What is an alkene?

A

Unsaturated hydrocarbons with a C=C double bond

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2
Q

What is the general formula of an alkene?

A

Cn H2n

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3
Q

Why is there no rotation about the C=C double bond?

A

Due to the π (pi) orbital - electron density above and below the single bond, which holds the carbon atoms in place.

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4
Q

Are they more or less reactive than alkanes? Why?

A

More reactive, due to high electron density of double bond and the fact the pi-bond is slightly easier to break.

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5
Q

What intermolecular forces of attraction do they have?

A

Only van der Waals due to non-polar bonds

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6
Q

Are they soluble in water? Why?

A

No, non-polar bonds (van der Waals’ < hydrogen bonding)

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7
Q

Name and describe the three kinds of isomers alkenes can have

A

Chain isomers (branched chains).

Position isomers (C=C on different carbon atom).

Geometric E-Z isomers (Z is when 2 highest atomic number chains are on the same side of the double bond; E is when they’re on opposite sides)

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8
Q

Write an equation for the complete combustion of pent-2-ene.

A

CH3CH=CHCH2CH3 + 7½O2 → 5CO2 + 5H2O

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9
Q

What is an electrophile?

A

Electron deficient atoms/ions which accept a pair of electrons (here, from the C=C double bond)

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10
Q

What is the most stable kind of carbocation intermediate? Why?

A

Alkyl groups have a positive inductive effect, so the most stable carbonation is the one bonded to the most other carbon atoms i.e. A tertiary carbocation

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11
Q

Major products will be formed from which kinds of carbocations?

A

Tertiary (or the most stable available)

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12
Q

What conditions are needed for the electrophilic addition of H2O to an alkene?

A

Acid catalyst, usually phosphoric acid

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13
Q

What are the product(s) of the reaction?

A

An alcohol

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14
Q

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

A

Room temperature

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15
Q

What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?

A

Room temperature and organic solvent

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16
Q

How does a molecule with a non-polar bond react as if it is an electrophile?

A

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule → δ+ atom attracted to double bond

17
Q

How would you turn the product into an alcohol and how does show that sulfuric acid catalyses the addition of water to an alkene?

A

Add water.

H₂SO₄ reforms, showing it catalyses the hydration of alkenes

18
Q

What is an addition polymer?

A

many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule

19
Q

What are monomers? What form do they usually take?

A

Molecules which combine to form a polymer.

Usually have a C=C bond which breaks to leave a repeating pattern.

20
Q

Give 3 uses of poly(chloroethene) / PVC

A

Drainpipes

Vinyl

Aprons

21
Q

Give two examples of plasticisers

A

esters and phthalates

22
Q

What are plasticisers?

A

Small molecules that get between polymer chains to force them apart and allow them to slide over one another.

23
Q

How do the physical properties of PVC change due to a plasticiser? What applications does this lead to?

A

PVC with a plasticiser become flexible, used for aprons.

Without a plasticiser, PVC is rigid, used for drainpipes.

24
Q

Why do things containing mainly C-C and C-H bonds not decompose easily?

A

Bonds are non-polar so are not attacked by enzymes

25
Q

Why is a lack of biodegradability in compounds with C-C or C-H bonds a problem?

A

Disposal is very problematic

26
Q

What is mechanical recycling?

A

Where plastics are separated into different types, washed, ground down, melted and re-moulded.

27
Q

What is mechanical recycling used for?

A

Soft drinks bottles → fleeces

28
Q

What is feedstock recycling?

A

Plastics heated to a temperature which break polymer bonds, leaving original monomers that can be made into new plastics.

29
Q

What is feedstock recycling used for?

A

Making totally new plastics

30
Q

What is a problem with recycling?

A

Each time thermosoftening plastics are melted and remoulded, their properties degrade, so they can only be remoulded a limited number of times.

A-Level Chemistry (16 decks)

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