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GCSE Chemistry > C9 - Crude Oil and Fuels > Flashcards

C9 - Crude Oil and Fuels Flashcards

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1
Q

What is Crude Oil and what are its uses?

A

Crude Oil is a dark, smelly liquid formed over millions of years from the remains of plankton buried in mud under the sea.

It is a non-renewable resource used for fuel, plastics and other products.

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2
Q

What is Crude Oil a mixture of?

A

A MIXTURE of different carbon compounds - mostly hydrocarbons.

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3
Q

What is a hydrocarbon?

A

A hydrocarbon is a chemical compound that ONLY contains hydrogen and carbon atoms.

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4
Q

Why can Crude Oil straight from the ground not be used?

A

It contains too many substances with different boiling points.

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5
Q

What is Crude Oil separated into? What are they?

A

‘Fractions’ - substances with similar boiling points.

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6
Q

How is Crude Oil separated into fractions?

A

Fractional Distillation

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7
Q

What are most of the hydrocarbons in Crude Oil called?

A

Alkanes

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8
Q

What are Alkanes?

A

Alkanes are ‘saturated hydrocarbons’.

They contain as many hydrogen atoms as possible, and all the carbon-carbon bonds are single covalent bonds.

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9
Q

What do all named Alkanes end in?

A

‘ane’

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10
Q

What are the prefixes for the alkanes based on the number of carbon atoms within each molecule?

A 
1 Carbon = Meth-
2 Carbons = Eth-
3 Carbons = Prop-
4 Carbons = But-
5 Carbons = Pent-
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11
Q

What are the names and formulae for the first 5 alkane molecules? What state are they in?

A

Methane - CH4 (g)
Ethane - C2H6 (g)
Propane - C3H8 (g)
Butane - C4H10 (g)

Pentane - C5H12 - (l) LIQUID

All are gases except pentane.

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12
Q

Based on the first 4 alkanes, what is the general formulae for an alkane?

A

CnH(2n+2)

Essentially, for every carbon atom, there are 2 times the hydrogen atoms, plus 2.

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13
Q

How can alkanes be visually represented?

A

Displayed formulae:

A diagram of all the single covalent bonds between the carbon-carbon bonds and the carbon-hydrogen bonds.

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14
Q

How can you work out whether a displayed formula (diagram) is an alkane?

A

You have to see of it fits the general formula:

1) Count the number of Carbon Atoms
2) Apply the (2n+2) rule for the Hydrogen Atoms.
3) Then count the number of Hydrogen Atoms and see if it matches the answer you calculated using the (2n+2) rule.

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15
Q

What is the aim of fractional distillation?

A

To separate crude oil into manageable fractions, each with similar boiling points.

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16
Q

What factor determines the properties of each fraction?

A

The size/length of the hydrocarbon molecule chains.

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17
Q

What sized hydrocarbons have a higher boiling point? Short or Long Chains.

A

Long chains - because there is more matter to boil.

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18
Q

What is the volatility of a substance?

A

Its tendency to turn into a gas.

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19
Q

What sized hydrocarbons have a greater volatility? Short or Long Chains.

A

Short chains - because they have a lower boiling point than longer-chain molecules.

*whence why you can smell petroleum gas (petrol) in the air - made out of short-chain molecules (pentane to decane)

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20
Q

What is the viscosity of a substance?

A

How easily it flows.

Low viscosity = runny
High viscosity = thick

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21
Q

What sized hydrocarbons have a greater viscosity? Short or Long Chains.

A

Long chains - because short chains have weak intermolecular forces (making it runny).

*whence why pentane (longer chain) is a liquid (stronger intermolecular forces).

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22
Q

What sized hydrocarbons have greater flammability? Short or Long Chains.

A

Short chains - because of the weak intermolecular forces between the molecules.

*whence why methane is a highly flammable gas.

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23
Q

Why do short-chain molecules make better fuels?

A
  • They are more flammable - so easy to ignite.

- They are more volatile - because of their lower boiling point

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24
Q

What type of flames do short-chain molecules burn with?

A

A clean, unsmoky flame

25
Q

What is the name of the tall tower/column that Crude Oil is fed into?

A

A fractionating column

26
Q

What is Crude Oil fed into the fractionating column as?

A

It is heated and then fed into the fractionating column as hot vapour.

27
Q

How does the temperature of the column differ from top to bottom?

A

The column is very hot at the bottom and gets progressively cooler towards the top.

28
Q

How do the gases (vapour) move in the column?

A

The various gases move up the column and condense at the boiling point which corresponds to the boiling point of the hydrocarbon molecules.

29
Q

How and in what state are the different fractions collected?

A

They are continually collected as liquids where they will be further refined to be used.

30
Q

Where are the short-chain hydrocarbon molecules collected?

A

At the top of the tower due to the lower boiling point and higher volatility.

*e.g methane

31
Q

Where are the long-chain hydrocarbon molecules collected?

A

At the bottom of the tower due to the higher boiling point and lower volatility.

*e.g pentane

32
Q

What is ‘burning’ known as in Chemistry?

A

Combustion

33
Q

What is meant by the term ‘complete combustion’?

A

It means that there is a good supply of air (oxygen).

34
Q

What are the 2 products of the complete combustion of a hydrocarbon?

A

Carbon Dioxide and Water

35
Q

What would the word equation be for the complete combustion of propane?

A

Propane + Oxygen —> Carbon Dioxide + Water

36
Q

What happens to the carbon and hydrogen in the hydrocarbon when it is completely combusted?

A

They are oxidised completely.

37
Q

What is the chemical test for CO2?

A

Turns limewater cloudy.

38
Q

What are the 2 chemical tests for water?

A

1) Turns anhydrous copper sulfate paper blue.

2) Turns blue cobalt chloride paper pink.

39
Q

What is meant by the term ‘incomplete combustion’?

A

When there is not a good air supply (oxygen). (*Think of a blocked chimney).

40
Q

What is produced by the incomplete combustion of a hydrocarbon?

A

Carbon Monoxide (CO) and Water

41
Q

Why is Carbon Monoxide produced and not CO2 for the incomplete combustion of a hydrocarbon?

A

There is not enough oxygen available.

42
Q

What is Carbon Monoxide?

A

A toxic, invisible gas that is colourless and odourless.

43
Q

Why is Carbon Monoxide so dangerous for humans?

A

Carbon Monoxide binds extremely well to the heamoglobin in our blood cells (even more so than oxygen). This means it is easily transported around the body.

44
Q

How should you balance hydrocarbon equations?

A

In the order of CHO.

Carbon first, then hydrogen, then oxygen.

45
Q

How can larger hydrocarbon molecules be broken up into smaller, more useful hydrocarbon molecules?

A

By a process called ‘cracking’.

46
Q

What type of reaction is ‘cracking’? Is it exothermic or endothermic?

A

A thermal decomposition reaction - endothermic.

47
Q

Where and in what vessel does cracking usually take place?

A

Steel vessels called crackers - found at oil refineries.

48
Q

What happens in a cracker?

A

The specific fraction of crude oil is heated until it is vapourised.

49
Q

What 2 things can happen to the hot vapour?

A

1) The vapour is passed over a hot catalyst. CATALYTIC CRACKING (INDUSTRY)

OR

2) The vapour is mixed with steam and heated to a very high temperature. THERMAL CRACKING

50
Q

What types of hydrocarbons does cracking produce?

A

Cracking produces both saturated (alkanes) and unsaturated (alkenes) hydrocarbons.

51
Q

What are alkenes?

A

Alkenes are unsaturated hydrocarbons that contain at least one double bond between their carbon atoms C=C.

Examples:
ethene, propene etc…
*prefixes are still the same eth-, prop-, but-

52
Q

What is the word and chemical equation for the cracking of Decane, C10H22, which produces Pentane, Propene and Ethene?

A

Decane (500°C + catalyst) —> Pentane + Propene + Ethene

C10H22 —> C5H12 + C3H6 + C2H4

*Here you can see that Pentane, which is used in petrol for cars, is the most useful substance produced from this example of cracking.

53
Q

How do alkenes and alkanes compare in terms of reactivity? Which one is used in fuels and why?

A

-Alkenes are generally more reactive than alkanes due to the double bond between the carbon atoms.

  • Alkanes are used in fuels as they can react with more oxygen, due to the fact that they hold the maximum number of hydrogen atoms possible.
  • Alkenes are NOT used in fuels because they are very smoky when they burn - they tend to undergo incomplete combustion. Alkenes release far less energy when burned.
54
Q

What is the diagnostic lab test for an alkene?

A

Alkenes turn orange bromine water colourless.

55
Q

What are alkenes used in?

A

They are useful in making plastics.

56
Q

What are the first 4 common alkenes? Which are gases and which are liquids ar room temperature after cracking in the lab?

A

Ethene, C2H4 (gas)
Propene, C3H6 (gas)
Butene, C4H8 (gas)
Pentene, C5H10 (liquid - long enough - stronger intermolecular forces)

*Chemical Formula Tip —> Double the number of hydrogen atoms as carbon atoms. (CnH2n)

METHENE DOES NOT EXIST - CANNOT HAVE AN ALKENE WITH ONLY ONE CARBON.

57
Q

What is used as the catalyst for thermal cracking in the lab?

A

Broken pot.

58
Q

Why are Pentane and Pentene the first alkane and alkene to be a liquid at room temperature?

A

As the chain length increases, the melting and boiling points of the molecules also increases - meaining that room temperature isn’t hot enough to make pentane or pentene a gas.

Also, the longer the chain, the stronger the intermolecular forces.

Pentene is the shortest alkene that is a liquid.
Pentane is the shortest alkane that is a liquid.

59
Q

How do you draw the displayed formula for alkenes?

A
  • First draw all the carbon atoms out.
  • Make one of the carbon-carbon bonds a double bond (C=C)
  • Draw the the correct number of hydrogens around the carbon’s.

Example: (C2H4 - Ethene)

         H   H
         |    |
         C = C
         |    |
         H   H

GCSE Chemistry (17 decks)

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