Topic 9 - Crude oil and fuels

Question 1

What kind or resource is crude oil?

Answer 1

A finite resource.

Question 2

What can crude oil be used for (when separated into different compounds)?

Answer 2

Combustion, to move cars or to generate heat.

Question 3

How is crude oil formed and where is it found?

Answer 3

It is formed over millions of years as the remains of sea creatures (containing a large amount of carbon) have rock form on top of them, creating conditions like high temperatures and high pressure, to make crude oil. It is found in rocks in under the Earth’s surface.

Question 4

What is crude oil like?

Answer 4

A viscous, smelly liquid that is a mixture of different carbon compounds. This means these compounds are not bonded together.

Question 5

What are hydrocarbons?

Answer 5

Chains of only hydrogen and carbon atoms bonded together to make chemical compounds, these make up most of the compounds in crude oil.

Question 6

When separating crude oil, what is the name for the different chemical compounds in the mixture?

Answer 6

Fractions.

Question 7

What is the name of the process by which fractions of crude oil are separated out from the mixture?

Answer 7

Fractional distillation.

Question 8

What are alkanes?

Answer 8

Saturated hydrocarbons, meaning all carbon-carbon bonds are single covalent bonds, unlike alkenes which have a carbon-carbon double bond. No more hydrogen atoms can be added to an alkane.

Question 9

What is the formula for each of the first 4 alkanes?

Answer 9

CH4 = Methane.
C2H6 = Ethane.
C3H8 = Propane.
C4H10 = Butane.

Question 10

What is the general formula for alkanes?

Answer 10

C(n)H(2n+2)

Question 11

What characteristic do hydrocarbons have that make them a good fuel?

Answer 11

They are very flammable.

Question 12

How does fractional distillation work?

Answer 12

When heating the crude oil, the temperature gets cooler going up the column, since different compounds have different boiling points, they condense into a liquid at different heights in the fractionating column and thus separate into different compounds fully.

Hydrocarbons with the smallest number of atoms have the lowest boiling points, they cool to form liquids.

Question 13

What is complete combustion?

Answer 13

When a hydrocarbon is burned, if it goes through complete combustion, it will not produce any soot and react quickly. This happens when oxygen supply is plentiful.

Question 14

Write the word equation for the complete combustion of propane.

Answer 14

Propane + Oxygen ——> Carbon Dioxide + Water

Question 15

What is incomplete combustion?

Answer 15

When oxygen is in limited supply, combustion will form Carbon Monoxide (CO) instead of Carbon Dioxide (CO2), Carbon Monoxide is a toxic poisonous gas which can kill a human if inhaled too much as it takes the place of oxygen in the blood stream and prevents breathing.

Question 16

What is ‘cracking’ of hydrocarbons?

Answer 16

When larger, less useful hydrocarbon molecules can be broken down into smaller, more useful ones.

Question 17

How does ‘cracking’ hydrocarbons work?

Answer 17

It takes place at an oil refinery and a heavy fraction of distilled crude oil is heated to vaporise the hydrocarbons.

The vapour is then either
-passed over a hot catalyst
-mixed with steam and heated to extreme temperatures.

The hydrocarbons are cracked as thermal decomposition reactions take place, i.e. larger particles break to form smaller ones.

Question 18

What three hydrocarbons can be produced by cracking Decane (C10H22)?

Answer 18

Pentane (C5H12), Propene (C3H6) and ethene (C2H4).

Question 19

What is an alkene?

Answer 19

An unsaturated hydrocarbon, which has a carbon-carbon double covalent bond, which means hydrogen atoms can be added to it to form its alkane version. As carbon atoms form four bonds and the carbon-carbon double bond takes up two bonds, two carbons can only bond to two hydrogens. Alkenes are typically more reactive than alkanes.

Question 20

How do we test for an alkene?

Answer 20

We add the hydrocarbon to bromine water, to test whether the hydrocarbon is saturated and can bond with the bromine since it has/has not got a double bond. If the hydrocarbon is an alkene it will have turned the orange bromine water colourless.

Question 21

What is crude oil classified as?

Answer 21

A dark, viscous and pungent liquid that is a mixture of hydrocarbons.

Question 22

What type of distillation is used to separate crude oil?

Answer 22

Fractional distillation

Question 23

What are the different compounds in crude oil called?

Answer 23

Fractions

Question 24

What are saturated hydrocarbons?

Answer 24

Hydrocarbons where all of the bonds between carbon atoms are single covalent bonds.

Question 25

What is a general formula?

Answer 25

A chemical formula using n to represent the ratio of molecules in a homologous series

Question 26

What does it mean for a compound to be flammable?

Answer 26

It catches fire/combusts easily.

Question 27

What happens to boiling point as the size of a hydrocarbon chain increases?

Answer 27

It increases

Question 28

What happens to volatility as size of a hydrocarbon molecule increases?

Answer 28

It decreases

Question 29

What is viscosity?

Answer 29

How thick a substance is

Question 30

What happens to viscocity as size of a hydrocarbon molecule increases?

Answer 30

It increases

Question 31

What happens to flammability as size of a hydrocarbon molecule increases?

Answer 31

It decreases

Question 32

Which hydrocarbon molecules are condensed at the top of a fractionating column?

Answer 32

The smallest molecules with the lowest boiling points.

Question 33

What happens to limewater when a gas from combustion is pumped through it?

Answer 33

The limewater becomes cloudy as carbon dioxide is pumped through it

Question 34

What is the process of cracking hydrocarbons called?

Answer 34

Thermal decomposition

Question 35

Why are hydrocarbons cracked?

Answer 35

Longer chain molecules are less useful than shorter chain ones, so the length is often reduced by cracking.

Question 36

What is the defining feature of alkenes?

Answer 36

They have a double bond between two carbon atoms

Question 37

What is the positive test for an unsaturared hydrocarbon?

Answer 37

It turns orange bromine water colourless