C9 - Crude oil and fuels

Question 1

What is meant by the term ‘hydrocarbon’?

Answer 1

A molecule made from Carbon and Hydrogen atoms ONLY

Question 2

What is the difference between a saturated and an unsaturated hydrocarbon?

Answer 2

A saturated hydrocarbon (eg alkane) does not contain a C=C double bond. An unsaturated hydrocarbon (eg alkene) does contain a C=C double bond and can undergo addition reactions.

Question 3

What is the name given to molecules which share the same molecular formula but have different structures?

Answer 3

Isomer

Question 4

Where are alkanes found naturally?

Answer 4

Crude oil or natural gas

Question 5

Name the first 6 alkanes.

Answer 5

• Methane
• Ethane
• Propane
• Butane
• Pentane
• Hexane

Question 6

What is the general formula for the alkanes?

Answer 6

CnH(2n+2)

Question 7

True or false: Butane and methyl propane are isomers?

Answer 7

True

Question 8

Which substances are made when an alkane burns undergoing complete oxidation?

Answer 8

• Water
• Carbon dioxide

Question 9

What is meant by the term ‘homologous series’?

Answer 9

A homologous series is a group of organic compounds that have similar chemical properties and have trends in their physical properties (eg boiling points). Each member of the homologous series differs from the previous by a CH2 unit.

Question 10

Describe what is meant by ‘complete’ and ‘incomplete’ combustion.

Answer 10

• Complete combustion occurs in excess oxygen, producing carbon dioxide
• Incomplete combustion occurs in limited oxygen, producing soot and carbon monoxide

Question 11

What compound has the formula CO, and why is it dangerous?

Answer 11

Carbon monoxide, poisonous

Question 12

Which equation represents incomplete combustion?

Answer 12

Equation b) C2H6 + 3.5O2 ——2CO2 + 3H2O

Question 13

What is the general formula for an alkene?

Answer 13

CnH2n

Question 14

What is the name of the alkene with 5 carbons?

Answer 14

Pentene

Question 15

Why is there no such molecule as ‘methene’?

Answer 15

An alkene contains a C=C double bond; the smallest alkene is ethene, not methane.

Question 16

Why are alkenes more reactive?

Answer 16

Alkenes are unsaturated and contain a C=C double bond that reacts by one of them opening up and reacting.

Question 17

What is the molecular formula of propene?

Answer 17

C3H6

Question 18

What colour is bromine water?

Answer 18

Orange

Question 19

What happens to bromine water if it is added to an alkene?

Answer 19

Changes colour from Orange to colourless

Question 20

What type of chemical reactions do alkenes undergo?

Answer 20

Addition

Question 21

Write a chemical equation for the reaction between ethene and bromine water and name the product.

Answer 21

CH2CH2 + Br2 ——CH2BrCH2Br
1,2-dibromoethane

Question 22

What is crude oil?

Answer 22

A mixture of hydrocarbons

Question 23

Name the process by which crude oil is separated into its separate components.

Answer 23

Fractional Distillation

Question 24

Why does fractional distillation work?

Answer 24

The molecules in crude oil have different boiling points and can be separated.

Question 25

Is the hottest part of the fractionating tower at the top or the bottom?

Answer 25

Bottom

Question 26

Which fraction has the lowest boiling point?

Answer 26

Refinery gases

Question 27

Which fraction has the highest boiling point?

Answer 27

Bitumen

Question 28

True or False: Refinery gases have a high boiling point so they will condense at the top of the tower.

Answer 28

FALSE: Refinery gases have a LOW boiling point so they will condense at the top of the tower.

Question 29

What happens to the viscosity of the fractions as you move down the fractionating tower?

Answer 29

Viscosity increases

Question 30

What happens to the boiling points of the fractions as you move up through the fractionating tower?

Answer 30

The boiling points decrease

Question 31

True or False: When a mixture of hydrocarbons is separated, the bonds within the molecules are broken.

Answer 31

FALSE: The weak bonds between the molecules are broken, NOT the strong covalent bonds between the atoms.

Question 32

What happens to the flammability of the hydrocarbons as you descend the fractionating tower?

Answer 32

Flammability decreases

Question 33

Which gas reduces the capacity of the blood to carry oxygen?

Answer 33

Carbon monoxide

Question 34

Which hydrocarbons are most useful and why?

Answer 34

Smaller ones as more flammable (used as fuels)

Question 35

When fuels burn in car engines, what unreactive gas in the air burns too?

Answer 35

Nitrogen oxides

Question 36

What type of pollution does nitrogen oxides cause?

Answer 36

Acid rain

Question 37

Many fuels contain sulfur. What gas is produced when sulfur burns?

Answer 37

Sulfur dioxide

Question 38

What type of pollution does sulfur dioxide cause?

Answer 38

Acid rain

Question 39

Why would a chemist know that carbon dioxide, nitrogen dioxide, and sulfur dioxide are all acidic gases?

Answer 39

They are all non-metal oxides

Question 40

Give two harmful effects of acid rain.

Answer 40

* Makes lakes and rivers too acidic for aquatic life * Damages buildings and statues

Question 41

For which hydrocarbons is there a greater demand?

Answer 41

Smaller chain hydrocarbons

Question 42

Fractional distillation does not provide enough petroleum to meet the demand. How is this issue resolved?

Answer 42

By Cracking

Question 43

What are the conditions needed for Cracking?

Answer 43

* High temperature * Aluminium oxide (alumina) catalyst

Question 44

Complete the equation: _________-------- C2H4 + C6H14.

Answer 44

C8H18

Question 45

Complete this equation: C15H32 ----- C8H18 + C4H8 + ______.

Answer 45

C3H6

Question 46

True or False: When a long chain alkane is cracked into three smaller short chain molecules, two alkanes and an alkene are produced.

Answer 46

FALSE: There must always be an alkene and an alkane in the products.

Question 47

How could you prove that at least one of the products of cracking was an alkene?

Answer 47

Use bromine water, it will change colour from orange to colourless.

Question 48

Why does petrol have a lower boiling point than diesel?

Answer 48

Diesel is made from longer chain hydrocarbons that have stronger attractive forces.

Question 49

In cracking, how are the physical properties of the smaller chain hydrocarbons different from the larger chain hydrocarbons they were formed from?

Answer 49

* Lower boiling points * Lower viscosity * Lower densities