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CHEMISTRY > ALKANES > Flashcards

ALKANES Flashcards

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1
Q

Define saturated

A

No double bond

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2
Q

Define hydrocarbon

A

Molecule containing only C and H

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3
Q

What two factors affect alkane boiling points

A

Carbon chain length, number of branches

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4
Q

Boiling point increases as chain length increases because:

A

•alkanes have induced dipole dipoles between molecules
•strength of bonds increases as size of molecule increases
•the longer the C chain, the bigger the molecule, the more e-

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5
Q

How do more branches affect boiling point?

A

•more branches decrease boiling point
•there is more surface contact between lower branched molecules
•the induced dipole dipole attractions between molecules of lower branched molecules are stronger

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6
Q

How does fractional distillation work?

A

Separates hydrocarbons based on their different boiling points

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7
Q

What is a fraction

A

A group of hydrocarbons with the same boiling point

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8
Q

What is the process of fractional distillation? (6m)

A

•crude oil is vapourised and enters column at the bottom
• the mixture of HC have different boiling points
•their boiling points depend on chain length and branching
•it is hotter at the bottom of the column
•larger molecules condense first at the bottom and collect

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9
Q

What is cracking?

A

Breaks larger fractions into smaller fractions

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10
Q

Why do we use cracking?

A

To produce more useful, shorter chain molecules that are higher in demand

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11
Q

What does thermal cracking use

A

High temperature and pressure

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12
Q

What temperature does thermal cracking use?

A

700-1200K

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13
Q

What pressure does thermal cracking use?

A

7000kPa

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14
Q

What are the products of thermal cracking?

A

One alkane, the rest alkenes

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15
Q

What temperature does catalytic cracking use?

A

720K

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16
Q

What pressure does catalytic cracking use?

A

100kPa

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17
Q

What catalyst does catalytic cracking use?

A

Zeolite

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18
Q

What is produced with catalytic cracking?

A

High percentage of branched alkanes and cycloalkanes

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19
Q

What are cycloalkanes used for?

A

Motor fuels

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20
Q

What is combustion?

A

Reaction with oxygen

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21
Q

What is needed for complete combustion

A

Excess oxygen

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22
Q

What are the products of complete combustion?

A

CO2 and H2O

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23
Q

What is the reaction for complete combustion of methane

A

CH4 + 2O2 -> CO2 + H20

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24
Q

What is methane used for?

A

Domestic heating and cooking

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25
Q

What are products of incomplete combustion?

A

CO and H20

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26
Q

Why is CO harmful

A

Toxic as it prevents oxygen from binding to haemoglobin in blood cells

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27
Q

What are two harmful products of combustion

A

SO2 and NO2

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28
Q

Equation for production of SO2

A

S(s) + O2 -> SO2

29
Q

Why is sulfur dioxide formed?

A

Sulfuric impurities appear in crude oil

30
Q

What does sulfur oxide and nitrogen oxide cause

A

Acid rain

31
Q

Why is acid rain harmful

A

Causes erosion of buildings and lake contamination

32
Q

What does sulfur dioxide do in rain water

A

Dissolve

33
Q

Give the equation of the reaction of SO2 with rain water

A

SO2 + 1/2 O2 + H2O -> H2SO4

34
Q

Why are nitrogen oxides formed after combustion?

A

Fuels burn in air which is 80% oxygen

35
Q

Give equation for the formation of nitrogen oxide

A

N2 + O2 -> 2NO

36
Q

Give equation for the formation of nitrogen dioxide

A

2NO + O2 -> 2NO2

37
Q

What is the equation with nitrogen that causes acid rain

A

4NO2 + 2H2O + O2 -> 4HNO3

38
Q

Why are unburnt hydrocarbons harmful

A

Toxic and cause cancer

39
Q

How do unburnt hydrocarbons arise

A

Escape into air before being used up

40
Q

What are the two ways to reduce pollution

A

Fluent gas desulphurisation and catalytic converter

41
Q

How does flue gas sulphurisation work

A

Neutralises acidic SO2 with alkali

42
Q

What does flue gas desulfurisation use

A

Calcium oxide and calcium carbonate

43
Q

What does the reaction with calcium oxide and SO2 produce

A

CaSO4.2H2O

44
Q

What is CaSO4.2H2O used for

A

Builders’ plaster

45
Q

What does calcium carbonate and SO2 produce

A

CaSO4

46
Q

How does a catalytic converter work?

A

Converts harmful gases into less harmful gases

47
Q

What is the structure of a catalytic converter?

A

Honeycomb

48
Q

Why does a catalytic converter have a honeycomb structure?

A

Increased surface area for a faster rate of reaction

49
Q

What metals is a catalytic converter made of

A

Platinum and rhodium (catalysts)

50
Q

What does NO and CO produce in a catalytic converter?

A

N2 and CO2

51
Q

What do unburnt hydrocarbons and NO produce in a catalytic converter

A

CO2 H2O N2

52
Q

Polluting effect of CO2

A

Greenhouse gas

53
Q

Polluting effect of H2O

A

Greenhouse gas

54
Q

Polluting effect of CO

A

Poisonous

55
Q

Polluting effect of solid Carbon

A

Damages lungs

56
Q

Three characteristics of the homologous series are:

A

•differ by CH2
•chemically similar
•show a trend in physical properties

57
Q

The order of fractions from lowest boiling point to highest

A

Mineral oil, gas oil (diesel), kerosene (paraffin), naphtha, petrol (gasoline)

58
Q

What does the term carbon-neutral mean?

A

An activity with no overall carbon emissions

59
Q

What is the use of a short chain alkane?

A

Fuel

60
Q

What is the use of a long chain alkane

A

Any of the high BP fractions eg. Fuel oil, kerosene, petrol

61
Q

Use of an alkene

A

Poly (alkene)

62
Q

How are nitrogen oxides formed in engines (2m)

A

•N2 reacts with oxygen IN AIR
•at high temperatures

63
Q

With which mechanism does chlorination occur?

A

Free-radical substitution

64
Q

What are the reagents and conditions of chlorination

A

Cl2 , UV light

65
Q

What are the steps in chlorination/free radical substitution?

A

•initiation
•propagation
•termination

66
Q

What is the equation of the initiation step of chlorination

A

UV light
Cl2 —-> 2Cl•

67
Q

What is the propagation step of chlorination of ethane?

A

Cl• + CH3CH3 –> •CH2CH3 + HCl
•CH2CH3 +Cl2 –> CH2ClCH3 + Cl•

68
Q

What is the termination step of chlorination?

A

Two radicals combine

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