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Crude Oil

Worksheet Overview

QUESTION 1 of 10

The oil that is pumped from the ground is called crude oil; before we can do much with it, we need to refine it. To see what that means, and why it's so important, we need to look a bit more carefully at what crude oil is like...

Crude oil is made of hydrocarbons; molecules containing hydrogen, carbon and nothing else. The hydrocarbons found in crude oil are a group called alkanes. All alkanes have similar looking structures; here are diagrams of the four smallest ones. You need to know their names, structures and chemical formulas.

If you look at the structures, you can see how similar the alkane structures are;

  • All alkanes have a chain of carbon atoms along their middle, called a backbone.
  • All the spare bonds around the carbon atoms are bonded to hydrogen atoms.
  • All the bonds in alkanes are single covalent bonds (one pair of shared electrons per bond).

Because of these rules, the chemical formula for all alkanes can be written as CnH2n+2. n has to be a whole number, but it can be any whole number. The alkanes in the picture are n = 1, 2, 3 and 4, but there are also alkanes with n =5, n = 20, even n = 50. If we know the number of carbon atoms in an alkane molecule, we can work out how many hydrogens there must be;

Pentane is the alkane with five carbons, so n = 5. We substitute n = 5 into CnH2n+2. (2 x 5) + 2 = 12, so pentane is C5H12.

Formation of crude oil

Crude oil is a fossil fuel, like coal and methane gas. Fossil fuels are formed from the remains of dead organisms. When small sea animals and plants die, they fall to the bottom of the sea, and get buried in layers of sediments. The layers of sediment gradually turn into rock, sealing the dead remains off from their surroundings. In particular, no oxygen can get to the remains. As the rocks are buried more deeply, they get hotter and more compressed. The resulting heat and pressure gradually turns them into oil and methane gas. This process happens very slowly- over millions of years. This means that oil that we use now will not be replaced for millions of years. From our point of view, crude oil is a non-renewable resource; once we use any crude oil, we are not going to get that oil back. That's why we need to be careful how we do use any oil, or other fossil fuels.

What is the name for oil that has just been pumped from the ground?

crude oil

dirty oil

natural oil

olive oil

What types of atom are present in hydrocarbons? Tick all the correct answers.

carbon

hydrogen

oxygen

water

Match the names with the chemical formulas for these molecules.

Column A

Column B

methane
CH4
ethane
C4H10
propane
C3H8
butane
C2H6

Look at this molecular structure;

Which of these are correct descriptions of this molecule? Tick all the right answers.

This is an alkene

This is a hydrocarbon

This is CH6

This is C2H6

This is an alkane

Look at this structure. Is this molecule an alkane?

Yes

No

We cannot be sure

Look at this molecular structure;

What is the name of this molecule?

Hexane is an alkane with six carbons (hex means six, like in hexagon). What is the chemical formula for hexane?

C6H6

C6H12

C6H14

C6H16

Which of these phrases describes crude oil? Pick a name and a reason.

C6H6

C6H12

C6H14

C6H16

Roughly how long does it take to convert dead remains of plants and animals into crude oil in nature?

A few days

A few years

Millions of years

The stages of making crude oil are jumbled up. Sort them into the right order, from beginning to end.

Column A

Column B

First
The remains are buried under layers of sediment
Second
Plant and animal remains fall to the bottom of the...
Third
The layers of sediment turn into rock
Fourth
The remains are heated and compressed without oxyg...
Final
The remains are converted into oil and methane gas...
  • Question 1

What is the name for oil that has just been pumped from the ground?

CORRECT ANSWER
crude oil
EDDIE SAYS
The oil pumped from the ground is called crude oil. It's not very useful, because it has many different types of molecule mixed up in it; that's because it formed naturally.
  • Question 2

What types of atom are present in hydrocarbons? Tick all the correct answers.

CORRECT ANSWER
carbon
hydrogen
EDDIE SAYS
Hydrocarbons are hydrogen, carbon and nothing else. That sounds quite limited, but there are still lots of possible structures.
  • Question 3

Match the names with the chemical formulas for these molecules.

CORRECT ANSWER

Column A

Column B

methane
CH4
ethane
C2H6
propane
C3H8
butane
C4H10
EDDIE SAYS
The part-words "meth", "eth", "prop", "but" are a kind of number system, meaning 1, 2, 3 and 4 in another language. They will come up again when we learn about another series of molecules, called the alkenes.
  • Question 4

Look at this molecular structure;

Which of these are correct descriptions of this molecule? Tick all the right answers.

CORRECT ANSWER
This is a hydrocarbon
This is C2H6
This is an alkane
EDDIE SAYS
Counting the atoms, there are two carbons and six hydrogens. Since there is hydrogen, carbon and nothing else, it is a hydrocarbon. All the bonds are single bonds, so this is also an alkane. We can also show this is an alkane because it follows the CnH2n+2 rule. There are two carbons, so n = 2, so there need to be (2 x 2) + 2 = 6 hydrogens.
  • Question 5

Look at this structure. Is this molecule an alkane?

CORRECT ANSWER
No
EDDIE SAYS
This structure isn't an alkane. The bond between the carbons is a double bond, and all the bonds in an alkane are single bonds. It doesn't follow the CnH2n+2 rule; there are two carbons, but only four hydrogens. (It's actually a molecule called ethene, which is really useful for making plastics... you will learn more about it in another activity.)
  • Question 6

Look at this molecular structure;

What is the name of this molecule?

CORRECT ANSWER
ethane
EDDIE SAYS
This is an alkane (all single bonds) with two carbons. In the language of carbon chemistry, the word for two carbons is "eth", so the name of the molecule is eth-ane.
  • Question 7

Hexane is an alkane with six carbons (hex means six, like in hexagon). What is the chemical formula for hexane?

CORRECT ANSWER
C6H14
EDDIE SAYS
Use the CnH2n+2 rule. There are six carbons, so n = 6. That means there must be (2 x 6) + 2 hydrogens, making 14 hydrogens.
  • Question 8

Which of these phrases describes crude oil? Pick a name and a reason.

CORRECT ANSWER
EDDIE SAYS
Crude oil is made from things which were alive, or dead organisms. That's where the "fossil" bit comes from. Converting the remains into oil happens very slowly- the next couple of questions are about the consequences of this.
  • Question 9

Roughly how long does it take to convert dead remains of plants and animals into crude oil in nature?

CORRECT ANSWER
Millions of years
EDDIE SAYS
In nature, the conversion of dead plants and animals into oil happens very slowly, over millions of years.
  • Question 10

The stages of making crude oil are jumbled up. Sort them into the right order, from beginning to end.

CORRECT ANSWER

Column A

Column B

First
Plant and animal remains fall to ...
Second
The remains are buried under laye...
Third
The layers of sediment turn into ...
Fourth
The remains are heated and compre...
Final
The remains are converted into oi...
EDDIE SAYS
The key thing here is that the plant and animal remains are sealed off under a layer of rock before being heated and compressed. If oxygen could get to them, they\'d probably just burn, and that isn\'t helpful for making crude oil.
---- OR ----

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