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OCR A level Chemistry Year 1 > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is a hydrocarbon

A

Compounds which only contain carbon and hydrogen

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2
Q

What is a saturated organic compound

A

One which contains only single bonds between carbon atoms

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3
Q

Are alkanes saturated or unsaturated

A

Saturated (single bonds)

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4
Q

What is the prefix for a carbon chain with 1 carbon

A

Meth-

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5
Q

What is the prefix for a carbon chain with 2 carbons

A

Eth-

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6
Q

What is the prefix for the carbon chain with 3 carbons

A

Prop-

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7
Q

What is the prefix for the carbon chain with 4 carbons

A

But-

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8
Q

What is the prefix for the carbon chain with 10 carbons

A

Dec-

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9
Q

What is the general formula for alkanes

A

CnH2n+2

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10
Q

What is a functional group

A

an atom or group of atoms that gives a compound its characteristic chemical reactivity

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11
Q

Do alkanes have a functional group

A

No

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12
Q

Define a homologous series

A

A series of compounds that have the same functional group and the same general formula, and in which successive members of the series differ by an extra- CH2- unit

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13
Q

Do alkanes for a homologous series

A

Yes

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14
Q

What are the types of covalent bonds

A
  • Sigma
  • Pi
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15
Q

What is a covalent bond

A

A shard pair of electrons

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16
Q

What are the 2 bonds in an alkane that are sigma bonds

A

C-C and C-H

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17
Q

What is a sigma bond

A

The result of the overlap of 2 orbitals, one from each bonding atom. This bond has 2 shared electrons

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18
Q

How many sigma bonds does each carbon have in an alkane

A

4 sigma bonds

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19
Q

In an alkane what is the bond angle around each carbon

A

109.5 because there are 4 sigma bonds so it’s tetrahedral

20
Q

What process splits crude oil into different fractions

A

Fractional distillation

21
Q

How is fractional distillation able to separate alkanes into different fractions

A

Since the alkanes have different boiling points, it increases as their chain length increases

22
Q

Why does the boiling point of alkanes increase

A

Due to the increased number of London forces, the more London forces the higher the boiling point

23
Q

Why do longer alkanes have a higher boiling point

A

The molecules have a larger surface area, so more surface contact is possible therefore there are more London forces which then require more energy to overcome

24
Q

Which alkane has a higher boiling point, pentane or 2-methylbutane, and why

A

Pentane because there is no branching

25
Q

Why do branched alkanes have a lower boiling point than straight chains

A

Because there are fewer surface points of contact between the molecules, giving fewer London forces

26
Q

What are the 3 reasons that alkanes lack reactivity

A
  • C-C and C-H sigma bonds are strong
  • C-C bonds are non-polar
  • The electronegativity of carbon ad hydrogen is so similar that the C-H bond can be considered to be non-polar
27
Q

What are the 2 productions of complete combustion of alkaned

A
  • Carbon dioxide
  • Water
28
Q

What reaction occurs when there is a limited supply of oxygen when reacting alkanes

A

Incomplete combustion

29
Q

During incomplete combustion of alkanes what are the 2 possible products other than water

A
  • Carbon monoxide
  • Carbon (soot)
30
Q

Why is carbon monoxide so toxic

A

Because it more readily binds to haemoglobin in blood which starves cells of oxygen

31
Q

What type of reaction, reacts alkanes with halogens

A

Substitution reaction, because a one or hydrogens are substituted for a halogen

32
Q

What is the condition that reacts halogens with alkanes

A

Sunlight / UV light

33
Q

Name this haloalkane, CH3BR

A

Bromomethane

34
Q

What are the 3 stages of a radical substitution

A
  • Initiation
  • Propagation
  • Termination
35
Q

In a radical substitution, what happens at the initiation stage (use bromine as your example)

A

The reaction is started when the covalent bond in a bromine molecule is broken by homolytic fission

36
Q

What is homolytic fission

A

When a covalent is broken and each atom takes of the electrons from the shared pair

37
Q

What happens to bromine during the initiation step in a radical substitution

A

2 bromine radicals are formed Br.

38
Q

What is a radical

A

An atom or group of atoms which has an unpaired electron

39
Q

What is the 2nd step in an radical substitution reaction

A

Propagation

40
Q

What happens during propagation in a radical substitution reaction (Bromine and methane)

A
  • CH4 + Br. -> CH3. + HBr
    (The bromine radical reacts with the C-H bond in methane forming a methyl radical and a molecule of hydrogen bromide)
  • CH3. + Br2 -> Ch3Br + Br.
    (Methyl radical reacts with a bromine molecule forming bromomethane and a new bromine radical)
41
Q

What makes propagation a chain reaction in a radical substitution reaction

A

Become it reactions continue to occur in a cycle

42
Q

What is the 3rd step in the radical substitution reaction

A

Termination

43
Q

What happens during termination of radical substitution

A

2 radicals collide, forming a molecule with all electrons paired

44
Q

What happens when 2 radicals collide

A

Both radicals are removed from the reaction mixture, stopping the reaction

45
Q

What are the 2 limitation of radical substitution in organic synthesis

A
  • Further substitution
  • Substitution at different positions in a carbon chain
46
Q

Why is further substitution a limitation to radical substitution

A

Because the reaction is continuous, more hydrogen can be substituted with halogens so would eventually produce a mixture of different haloalkanes or a compound with no hydrogen in
e.g. CH4 -> CH3Br -> CH2Br2 -> CHBr3 -> CBr4

47
Q

Why is substitution at different positions in a carbon chain a limitation to radical substitution

A

Different products would be formed due to them being isomers

OCR A level Chemistry Year 1 (17 decks)

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