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Chemistry 2.0 > 3.2 alkanes > Flashcards

3.2 alkanes Flashcards

1
Q

Define something saturated

A

Containing only single bonds

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2
Q

Define an alkane

A

Saturated hydrocarbons that contain only carbon-carbon and carbon-hydrogen single bonds

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3
Q

Define hydrocarbons

A

Compounds containing hydrogen and carbon atoms only

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4
Q

Define a fraction (1)

A

A mixture of compounds with similar boiling points

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5
Q

Name a laboratory technique used to separate isooctane (bp 125degrees) from a mixture of octane (bp 150degrees) and isoctane and outline how this occurs (3)

A
  • Name : Fractional distillation (1)
  • Isoctane has a lower boiling point compared to octane and will go to the top of the column first. (1)
  • The isoctane is condensed and cooled at the top of the column
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6
Q

State why fractional distillation is used to break down crude oil (1)

A
  • To seperate crude oil into mixtures of compounds with similiar boiling points/similiar sized molecules (1)
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7
Q

Give the name of the substance from which paraffin is obtained and state the name of the process used to obtain paraffin (2)

A
  • Substance : crude oil
  • Process : Fractional distillation
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8
Q

Sugest which element can be liquified easier between C3H8 and C4H10 (1)

A
  • (liquified means it starts from a gas so think of it as an inverse)
  • C4H10 can be liquified easier because it has a higher boiling point (1)
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9
Q

Suggest why dimethylpentane has a lower boiling point than that of its straigh chain isomer (2)

A
  • Molecule is smaller and molecules cannot get as close to feel van de waals forces (1)
  • Van de waals forces between intermolecular forces are weaker between the molecules (1)
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10
Q

State physical property of alkanes that allows them to be seperated from a mixture by fractional distillation (1)

A

Different boiling points (1)

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11
Q

Outline essential features of fractional distillation of crude oil that enable crude oil to be seperated into fractions (4)

A
  • Each molecule consists of different boiling points (1)
  • Boiling points depends on size/chain length/Mr (1)
  • Top of column is cooler and hence the compound with the lower boiling point will go to the top of the molecules (1)
  • Higher boiling point molcules stay at the bottom of the column
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12
Q

State 3 characteristics of the homologous series of compounds

A
  1. Differ by CH2
  2. They have the same general formula
  3. They are chemically similiar/react in same way
  4. Show a gradual change in physical properties
  5. They have same functional group
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13
Q

Crude oil is seperated into fractions by fractional distillation. Outline how different fractions are obtained by this process (3)

A
  • Crude oil is heated to vapourise it (1)
  • Vapour is passed into fractionating column (1)
  • Top of the tower is cooler than the bottom as fractions are seperated by boiling points (1)
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14
Q

What are the five fractions obtained by fractional distillation of crude oil (in order)

A
  1. Lubricating oil
  2. Diesel
  3. Paraffin
  4. Naptha
  5. Gasoline
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15
Q

Two reasons why Fractions collect at different temperatures (2)

A
  • Negative temperature gradient/ temperature of the column decreases upwards (1)
  • Larger molecules or heavier fractions condense at higher temperatures or lower down the column (1)
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16
Q

State conditions needed to carry out thermal cracking and type of product in high proportions

A
  • Condition : High temperature and high pressure
  • Product : One alkane with all other molecules being alkenes
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17
Q

State conditions needed to carry out catalytic cracking. Name catalyst and products formed

A
  • Conditions : high temperature, slight pressure and a catalyst
  • Zeolite
  • Cycloalkanes and branched alkanes
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18
Q

Complete eqaution to show cracking of one mole of hexadecane (C16H34) to form hexane and cyclopentane only

A

C16H34 -> C6H14 + 2C5H10

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19
Q

State the purpose of thermal cracking

A
  • To make alkenes/shorter molecules
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20
Q

Name polymer of but-2-ene

A

Polybut-2-ene

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21
Q

How does products show that reaction is an example of thermal cracking

A
  • Mainly alkenes formed
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22
Q

Suggest one important substance manufactured on a large scale from propene

A
  • Polypropene
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23
Q

Give a common use of an alkane

A
  • Jet fuel
  • Cracking
  • Diesel
  • Lubricant
  • Kerosene
  • Paraffin
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24
Q

State why thermal cracking is used to obtain a high yield of but-1-ene from C15H32

A
  • To produce prodcuts that are in greater demand/ more valuable/more expensive
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25
Q

State why high temperatues are needed for thermal cracking

A
  1. Break c-c bonds
  2. Break H-H bonds
  3. Break carbon chain
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26
Q

State a use of ethene

A
  1. Making plastics
  2. Make polymers
  3. Make ethanol

(plastics and polymers can be made from all ethenes)

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27
Q

State what is meant by the term cracking

A
  • Large molecules or compounds broken into smaller molecules
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28
Q

Three different carbon cations are formed by breaking c-c bonds in seperate molecules of butane during catalytic cracking. One of the structures is CH3CH2C+H2. Give structures of other two carbons

A

Structure 2 : C+H3
Structure 3 : CH3C+h2

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29
Q

One reason why cracking is important

A

To produce more valuable products/higher in demand

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30
Q

Show equation for complete combustion of decane

A

C10H22 +15.502->10C02+11H20

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31
Q

Show equation for incomplete combustion of hexane to form carbon monoxide

A

C6H14 +6.502->6C0+7H20

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32
Q

Show equation of incomplete combustion of pentsane to produce solid carbon particles

A

C5H12+3O2->5C6H20

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33
Q

Explain how oxides of nitrogen are formed in engines (2)

A
  • Oxygen and nitrogen react in the air
  • at high temperatures
34
Q

Why is it desirable emissions of oxides of nitrogen from vehicles

A

Formation of acid rain causes respiratory problems (as nitrogen monoxide can cause acid rain)

35
Q

Some carbon particulates are formed in diesel and oetrol vehicles. State why carbon particulates are formed

A

There is an incomplete combustion

36
Q

What is the equation of a reaction that removes nitrogen monoxide in a catalytic converter

A

2NO+2CO->N2+2CO2

37
Q

Suggest how partial blockage might affect performane of helicopter engine

A

Engine is less powerful
Needs to burn more fuel to get same energy
Costs increase due to need for more use of fuel

38
Q

Suggest why combustion of fuel in oil is likely to be incomplete

A

Difficult to supply sufficient air
Difficult to get enough oxygen for complete combustion

39
Q

Name gas that may be present because of complete incombustion and state reason why use of electrostatic precipitators could be a hazard if this gas was present

A

Carbon monoxide
- Reason : flammable

40
Q

Suggest why a kiln with a very fast air flow is likely to emit more sulfur dioxide than one with slower air flow

A
  • Increased oxygen supply so more sulfur compounds oxidised
  • Less contact time between SO2 and minerals
  • Less chance of reaction of SO2 if flow is fast
41
Q

What are the metals used in catalytic converters

A

Platinum, palladium, rhodium

42
Q

Thin layers of metals is used inside catayltic converters. Explain why thin layers are used ? (2)

A
  • To reduce amount of metals needed (M1)
  • Increase surface area or to give catalyst larger surface area (M2)
43
Q

State why sulfur compounds found in crude oil should be removed from the fractions before they are used for central heating fuel

A

Because in combustion SO2 is produced which causes acid rain

44
Q

Write an eqaution to show how nitrogen monoxide in air is converted into nitrogen dioxide

A

2NO + O2-> 2NO2

45
Q

State a hazard associated with the solid carbon

A

Breathing problems/damages lungs

46
Q

Identify a catalyst used in catalytic converter

A

Platinum
Palladium
Rhodium

47
Q

Explain why complete combustion of C4H10may contribute to enviromental problems

A

CO2 OR H20 when evolved is a greenhouse gas/ they are products of green house gases (1)
* they contribute to global warming (1)

48
Q

Identify a compound that is used to react with sulfur dioxide in products of combustion before they enter the atmosphere. Give a reason as to why the compound reacts with sulfur dioxide

A

Substance : Calcium oxixe
Reason : neutralisation occurs as calcium oxide is basic and SO2 is acidic so an acid base reaction happens

49
Q

Give one use of an alkane (e.g butane)

A

Fuel/LPG

50
Q

State meaning of term carbon neutral

A

An activity which has no net/overall annual carbon emmisions to the atmosphere

51
Q

Suggest one reason why a combustion may be incomplete

A

Not enough oxygen of air (enough to complete combustion)

52
Q

Why is catalyst coated on a ceramic honeycomb

A

Bigger surface area
increase reaction rate
ensures complete reaction

53
Q

Why is it beneficial to collect methane instead of letting it out into the atmosphere

A

Its a greenhouse gas

54
Q

If percentage of methane in air is greater than 15% explosion risk is much lower
One reason why there is a lower risk if percenage is greater than 15%

A

Not enough oxygen

55
Q

Suggest why the solid pollutant (carbon) is an enviromental problem

A

It causes global dimming/ causes breathing problems

56
Q

In polar regions that use diesel fuel may have ignition problems. Suggest one possible cause of a problem with diesel fuel

A

solidifies/freezes/goes viscous

57
Q

Write an equation to show how NO is formed and give a condition needed for its formation

A

1/2N2+1/2O2 ->NO
Condition : very high temperature

58
Q

An oxide of nitrogen contains 25.9% by mass of nitrogen. Determine empirical formula of this oxide

A

N205
In process use oxygen Mr as 16, not 32

59
Q

Why is NO a pollutant gas

A

It can lead to greenhouse gas emissions which leads to global warming

60
Q

Why is CaO coated on a mesh to remove sulfur dioxide

A

To react to sulfur dioxide

61
Q

Suggest why using CaO to remove sulfur dioxide may not be 100% efficient

A

All of sulfur dioxide may not react with calcium oxide

62
Q

Suggest why propane is suppilied as a liquid for use in camping stoves

A

Occupies a much smaller volume

63
Q

Fuel has been contaminated. Suggest how oil company might have recognised the problem before the petrol was sold

A

They could have done a quality controlm test or tested it before the sale

64
Q

Two reasons why boilers are designed to ensure complete combustion

A

Prevents release of toxic CO
More energy efficient (releases more energy on combustion)

65
Q

State term molecular formula

A

Actual numbers of atoms in each element

66
Q

State how a converter is constructed to maximise effect of the catalyst

A

Deposited in a ceramic honeycomb or mesh or sponge
To increase surface area of a catalyst

67
Q

Reasons for S02 in exhaust gases

A

Fractions/fuels/petrol contain sulphur

68
Q

State what is meant by term fuel

A

Releases heat energy when burned/ or a sourceful use of energy

69
Q

Why its desriable that none of sulfur containing impurites naturally found in crude oil are present in petroleum fractions (2)

A

Sulfur containing impurities burn to form SO2(1)
Leading to acid rain (1)

70
Q

Explain why NO is formed in petrol engines but is not readily formed when petrol burns in open air (3)

A
  • NO formed by reaction of nitrogen and oxygen in the air (1)
  • High combustion temperature (1) produces sufficient heat to break (1)
71
Q

Why removal of NO is desirable

A

It forms acid rain or toxic products (1)

72
Q

How are CO and NO removed

A

Catalyst converter is used and the catalyst used is rhodium.
Remember to show equation in the exams

73
Q

Which substance does not contribute to greenhouse effect
1. Carbon dioxide
2. Unburned hydrocarbons
3. Water vapour
4. Nitrogen

A
  1. Nitrogen
74
Q

What is homolytic fission

A

Splitting a bond to produce two particles that have a single unpaired electron

75
Q

What is hetrolytic fission

A

producing two particles which are different because one is a positive ion and the other is a negative ion

76
Q

What happens to chlorine in the photochemical reaction when ultraviolet initiates the following reaction alkane + chlorine -> chloroalkane + hydrogenchloride

A

homolytic fission to give free radicals

77
Q

Ethane and chlorine react to give a mixture of products
Which compound could be present in a mixture of compounds?
1. C5H12
2. C4H10
3. C3H7Cl
4. CH3Cl

A
  1. C4H10

because C2H5 radical is formed during reaction and during termination step two radicals combine

78
Q

Fractional distillation is used to seperate hydrocarbon mixture of crude oil by boiling point
What is the correct description of the fractional distillation?
1. Fractional distillation is a physical process that break the hydroarbon covalent bonds
2. Fractional distillation is a chemical process that break the hydrocarbon between the covalent bonds
3. Fractional distillation is a physial process that overcome the intermolecular forces between the hydrocarbon molecules
4. Fractional distillation is a chemical process that overcome the intermolecular forces between the hydrocarbon molecules

A

3
because seperating any chemical mixture by boiling point is a physical process and overcoming intermolecular forces is a physical process

79
Q

What hydrocarbon is in very high demand for transportation

A

petrol (octane) C8H18

80
Q

Explain the problem with producing haloalkanes via free-radical and give a solution

A

Further substitution can occur and the solution is to add excess alkane

Chemistry 2.0 (9 decks)

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