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Hydrocarbons Flashcards

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1
Q

How is crude oil formed?

A

Over millions of years, high temperatures and pressures cause the buried remains of plants and animals to turn into crude oil.

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2
Q

What is crude oil a mixture of?

A

Crude oil is a mixture of substances, most of which are hydrocarbons — molecules which are made of only carbon and hydrogen.

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3
Q

How are the different compounds in crude oil separated?

A

By fractional distillation.

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4
Q

What happens first in fractional distillation?

A

The oil is heated until most of it has turned into gas.
The gases enter a fractionating column, and the liquid bit (bitumen) is drained off at the bottom.

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5
Q

What kind of temperature gradient is in the column?

A

It’s hot at the bottom and gets gradually cooler as you go up.

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6
Q

What happens when a substance in crude oil reaches a part of the column cooler than its boiling point?

A

It condenses (turns back into a liquid).

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7
Q

Where do the longer hydrocarbons condense?

A

Near the bottom, where it’s hotter, because they have high boiling points.

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8
Q

Where do the shorter hydrocarbons condense?

A

Near the top of the column, where it’s cooler, because they have lower boiling points.

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9
Q

What do bubble caps do in the fractionating column?

A

They stop the separated liquids from running back down the column and remixing.

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10
Q

What is each fraction composed of?

A

A mixture of hydrocarbons with similar boiling points.

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11
Q

What kinds of hydrocarbons might a fraction contain?

A

Saturated or unsaturated hydrocarbons.

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12
Q

What is the difference between saturated and unsaturated hydrocarbons?

A
  • Saturated hydrocarbons only contain single bonds between carbon atoms
  • Unsaturated hydrocarbons have double or triple bonds between carbon atoms.
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13
Q

What is the approximate number of carbons in refinery gases and what are they used for?

A

~3; used in domestic heating and cooking.

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14
Q

What is the approximate number of carbons in gasoline (petrol) and what is it used for?

A

~8; used as a fuel in cars.

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15
Q

What is the approximate number of carbons in kerosene and what is it used for?

A

~15; used as a fuel in aircraft.

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16
Q

What is the approximate number of carbons in diesel and what is it used for?

A

~20; used as a fuel in some cars and larger vehicles, e.g. trains.

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17
Q

What is the approximate number of carbons in fuel oil and what is it used for?

A

~40; used as a fuel for large ships and in some power stations.

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18
Q

What is the approximate number of carbons in bitumen and what is it used for?

A

70+; used to surface roads and roofs.

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19
Q

Why are really long hydrocarbons not that useful?

A

Because they are viscous and have high boiling points — but they can be made smaller by cracking.

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20
Q

What is cracking?

A

Cracking is splitting up long-chain hydrocarbons into shorter ones.

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21
Q

What are the properties of long hydrocarbons?

A

High boiling points and are viscous (thick and gloopy).

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22
Q

What are the properties of shorter hydrocarbons?

A

Lower boiling points, much thinner and paler in colour.

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23
Q

Why is cracking necessary?

A

Demand for short-chain hydrocarbons like octane (used in petrol) is much higher than for long-chain ones.

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24
Q

What does cracking produce?

A

A mixture of shorter-chain alkanes and alkenes.

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25
What type of reaction is cracking
Thermal decomposition — breaking molecules down into simpler molecules by heating.
26
What is cracking used to produce besides fuels?
Alkenes, which are used to make polymers.
27
What are the industrial conditions for cracking?
Vaporised hydrocarbons passed over a powdered catalyst at about 600 °C - 700 °C.
28
What catalysts are used for cracking?
Silica (SiO₂) or alumina (Al₂O₃).
29
What is catalytic cracking?
Cracking using a catalyst.
30
What happens during the lab version of catalytic cracking?
The alkane is vaporised, then breaks down when it contacts the catalyst, producing shorter-chain alkanes and alkenes
31
Why is oil useful as a fuel?
Because a lot of energy is released when it’s burnt.
32
What is combustion?
A reaction where a substance is burned and reacts with oxygen, releasing heat energy.
33
Why are hydrocarbons good fuels?
Because their combustion reactions are very exothermic.
34
What are the products of complete combustion?
Carbon dioxide and water.
35
What is the word equation for complete combustion?
Hydrocarbon + oxygen → carbon dioxide + water.
36
What happens in incomplete combustion?
Not enough oxygen is present; products include carbon monoxide and soot, as well as CO₂ and H₂O.
37
Why is carbon monoxide dangerous?
- It combines with red blood cells and stops them carrying oxygen - Can cause fainting, coma or death.
38
What harmful gases are produced when fuels are burned?
Sulfur dioxide and nitrogen oxides.
39
Where does sulfur dioxide come from?
From sulfur impurities in hydrocarbon fuels.
40
How are nitrogen oxides formed?
At high temperatures, nitrogen and oxygen in the air react (often in car engines).
41
What happens when SO₂ and NOₓ mix with water in clouds?
They form dilute sulfuric acid and nitric acid.
42
What is acid rain?
Rain that contains sulfuric and nitric acid.
43
What are the effects of acid rain?
It causes lakes to become acidic, killing plants and animals.
44
What are alkanes?
Hydrocarbons — chains of carbon atoms surrounded by hydrogen atoms.
45
What is the general formula for alkanes?
CₙH₂ₙ₊₂
46
47
What are the names and formulas of the first five alkanes?
Methane: CH₄ Ethane: C₂H₆ Propane: C₃H₈ Butane: C₄H₁₀ Pentane: C₅H₁₂
48
What’s a way to remember the first four alkanes?
Mice Eat Peanut Butter.
49
Do alkanes burn in combustion reactions?
Yes — they combust completely in a good supply of oxygen.
50
Name the first five alkanes with molecular and structural formulas.
Methane: CH₄ – H-C-H Ethane: C₂H₆ – CH₃CH₃ Propane: C₃H₈ – CH₃CH₂CH₃ Butane: C₄H₁₀ – CH₃CH₂CH₂CH₃ Pentane: C₅H₁₂ – CH₃CH₂CH₂CH₂CH₃
51
What do combustion reactions of alkanes produce?
Carbon dioxide and water.
52
Give an example of an alkane combustion reaction.
Propane + oxygen → carbon dioxide + water
53
What do chlorine and bromine do in the presence of UV light?
React with alkanes to make haloalkanes.
54
What type of reaction is this? (chlorine and bromine)
Substitution reaction — a hydrogen atom is replaced by chlorine or bromine.
55
Give an example of a substitution reaction.
Methane + bromine → bromomethane + hydrogen bromide
56
What is the key structural feature of alkenes?
A double bond between two carbon atoms (C=C).
57
Are alkenes saturated or unsaturated?
Unsaturated — the double bond can open and form more bonds.
58
What is the general formula for alkenes?
CnH₂n
59
Name the first three alkenes.
Ethene: C₂H₄ – CH₂=CH₂ Propene: C₃H₆ – CH₃CH=CH₂ Butene: C₄H₈ – Two isomers: but-1-ene and but-2-ene
60
What do halogens do when they react with alkenes?
Form haloalkanes via addition reactions.
61
What happens in an addition reaction with alkenes?
The C=C double bond splits and a halogen atom is added to each carbon.
62
What is the reaction between bromine and ethene?
Ethene + bromine → dibromoethane
63
How is the bromine test for alkenes carried out?
Shake the alkene with orange bromine water — it goes colourless.
64
Why does bromine water go colourless with alkenes?
The bromine reacts with the alkene to make a colourless dibromoalkane.
65
Do alkanes react with bromine water?
No — they don’t have a double bond, so the solution stays orange.
66
Molecular formula of Methane
CH4
67
Structural formula of Methae
CH4
68
Molecular formula of Ethane
C2H6
69
Structural formula of Ethene
CH3CH3
70
Molecular formula of Propane
C3H6
71
Structural formula of Propane
CH3CH2CH3
72
Molecular formula of Butane
C4H10
73
Structural formula of Butane
CH3CH2CH2CH3
74
Molecular formula of Pentane
C5H12
75
Structural formula of Pentane
CH3CH2CH2CH2CH3
76
Molecular formula of Ethene
C2H4
77
Structural formula of Ethene
CH2CH2
78
Molecular formula of Propene
C3H6
79
Structural formula of Propene
CH3CHCH2
80
Molecular formula of Butene
C4H8
81
Structural formula of Butene
CH2CHCH2CH3 or CH3CHCHCH3
82
Molecular formula of Pentene
C5H10
83
Formula of Methanol
CH3OH
84
Formula of Methanol
C2H5OH
85
Formula of Propanol
C3H7OH
86
Formula of Butanol
C4H9OH

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