Chapter 9 Crude Oil and Fuels

Question 1

What are hydrocarbons?

Answer 1

Hydrocarbons are compounds that are only made up of hydrogen and carbon.

Question 2

Where do we get hydrocarbons from?

Answer 2

We obtain hydrocarbons from crude oil.

Question 3

What is crude oil?

Answer 3

Crude oil is a mixture of compounds but most are long and short-chained hydrocarbons.

Question 4

How is crude oil formed?

Answer 4

Crude oil is a non-renewable fossil fuel formed over a very long time from plankton.

Question 5

What is a homologous series?

Answer 5

Homologous series are groups of hydrocarbons with the same general formula and similar chemical properties.

Question 6

What is the general formula for alkanes?

Answer 6

Alkanes are a homologous series with the general formula:
CnH2n+2

Question 7

Give the prefixes for hydrocarbons with 1-10 carbons.

Answer 7

Prefixes are used when naming hydrocarbons to indicate how many carbon atoms are in the chain.

Number of Carbons Prefix
1 meth
2 eth
3 prop
4 but
5 pent
6 hex
7 hept
8 oct
9 non
10 dec

Question 8

How are alkanes named?

Answer 8

Alkanes are named by using the correct prefix and then ending in -ane.

Question 9

What is a saturated hydrocarbon?

Answer 9

Alkanes are saturated hydrocarbons. This means they only contain C-C single bonds.

Question 10

Name and give the molecular and displayed formula for the first 5 alkanes.

Answer 10

The first 5 alkanes are:

Question 11

Draw a diagram to show how fractional distillation is carried out in the lab and describe what it is used for.

Answer 11

Fractional distillation is a process used to separate mixtures of compounds based on their boiling points. In the lab we use this equipment:

Question 12

What property of hydrocarbons is used to separate the fractions of crude oil?

Answer 12

Fractional distillation is used to separate the compounds in crude oil based on their boiling points.

Question 13

Why is fractional distillation carried out on crude oil?

Answer 13

Fractional distillation processes crude oil into more useful products.

Question 14

Where is fractional distillation carried out?

Answer 14

During fractional distillation the crude oil is heated in a fractionating column

Question 15

What happens to the temperature as you move up a fractionating column?

Answer 15

The fractionating column is hottest at the bottom and gets cooler towards the top.

Question 16

Why are short chain hydrocarbons gases at room temperature?

Answer 16

Short chain hydrocarbons (like methane and ethane) are gases at room temperature due to weak intermolecular forces between the molecules so remain gases and are removed at the top of the column.

Question 17

What happens to intermolecular forces as the size of molecules increases? What does this result in?

Answer 17

As molecules increase in size the intermolecular forces increase. This results in high boiling points in large compounds. These remain at the bottom of the fractionating column.

Question 18

Draw and label a fractionating column to show the different fractions.

Answer 18

Fractionating column:

Question 19

List the 6 fractions and for each give the range of number of carbons in each and uses for each.

Answer 19

Question 20

What are feedstocks?

Answer 20

Feedstocks are chemicals that are used to make other more useful compounds.

Question 21

What are feedstocks used for?

Answer 21

The products of fractional distillation can be used to make feedstocks for the production of plastics and solvents.

Question 22

What do the properties of hydrocarbons depend upon?

Answer 22

The properties of hydrocarbons depend upon their size.

Question 23

What happens to the viscosity of hydrocarbons as the chain length increases?

Answer 23

The longer the hydrocarbon chain the more viscous (thicker/less runny) it is.

Question 24

What happens to the melting and boiling points as the hydrocarbon chain length increases?

Answer 24

As the length of the hydrocarbon chain increases the melting and boiling point increases.

Question 25

What happens to the volatility as the hydrocarbon chain length increases?

Answer 25

As the length of the hydrocarbon chain increases the volatility (how easily it evaporates and turns into a gas) decreases.

Question 26

What happens to the flammability as the hydrocarbon chain length increases?

Answer 26

As the length of the hydrocarbon chain increases the flammability (ability to catch fire) decreases.

Question 27

Write the word equation for the complete combustion of hydrocarbons.

Answer 27

Hydrocarbons are used as fuels because they burn in oxygen to produce energy. Carbon dioxide and water are produced.

Hydrocarbon + oxygen → carbon dioxide + water + energy

Question 28

Draw the equipment used to show the products of combustion and describe the changes shown in each test tube.

Answer 28

We can see the products of the complete combustion of hydrocarbons in the following demonstration:

Question 29

Write the word equation for incomplete combustion.

Answer 29

If there is not enough oxygen available then incomplete combustion occurs.

hydrocarbon + oxygen → carbon dioxide + water carbon monoxide + carbon + energy

Question 30

Why is carbon monoxide dangerous?

Answer 30

Carbon monoxide is poisonous.

Question 31

Why do we balance chemical equations?

Answer 31

Equations must be balanced so there is the same number of atoms of each element on each side of the arrow. Equations are balanced by changing the coefficient (number of molecules) of the compounds.

Question 32

Why do smaller hydrocarbons make better fuels?

Answer 32

Smaller hydrocarbons make better fuels because they are more flammable (ignite more easily) and burn with cleaner flames.

Question 33

What is cracking?

Answer 33

Cracking is a process where large hydrocarbons from crude oil are broken into smaller, more useful hydrocarbons.

Question 34

What type of hydrocarbon is always produced by fracking?

Answer 34

Cracking always produces hydrocarbons called alkenes which have C=C double bonds.

Question 35

What is the general formula for alkenes?

Answer 35

Alkenes are unsaturated hydrocarbons with the general formula:

CnH2n

Question 36

Why do alkenes tend to have smoky flames?

Answer 36

Alkenes tend to have smokey flames as they are more likely to incompletely combust than alkanes are.

Question 37

Name and give the molecular formula and displayed formula for the first 4 alkenes.

Answer 37

The first 4 alkenes are:

Name
Molecular Formula
Displayed Formula
ethene
C2H4

propene
C3H6

butene
C4H8

pentene
C5H10

Question 38

What hydrocarbons are produced from cracking?

Answer 38

When a large hydrocarbon is cracked an alkene and an alkane are produced. The number of carbon atoms and hydrogen atoms on either side of the arrow must balance.

Question 39

Name the 2 types of cracking.

Answer 39

There are 2 types of cracking, catalytic cracking and steam cracking.

Question 40

What happens in catalysis cracking?

Answer 40

In catalytic cracking the hydrocarbon is vapourised and passed over a hot catalyst.

Question 41

Why is cracking described as thermal decomposition?

Answer 41

Cracking is an example of thermal decomposition. This is because a compound is broken down using heat.

Question 42

What compounds react with bromine water?

Answer 42

Compounds containing C=C double bonds react with orange bromine water. The bromine water turns from orange to colourless as the bromine atoms add across the double bond.

Question 43

What is the positive test for an alkene?

Answer 43

The positive test for an alkene is that it decolourises bromine water.