NATIONAL 5 CHEMISTRY

UNIT 2 NATURE’S CHEMISTRY

Contents Homologous series

•Fuelling Scotland’s future

•Alkanes

•Alkenes

•Cycloalkanes

Fuelling Scotland’s Future

•As North Sea gas and oil runs out Scotland will become dependent on imported gas unless new sources can be identified and exploited.•In the second half of the 19th century and the start of the 20th century Scotland had a thriving shale oil industry.• In 1847 the Scottish chemist James Young prepared "lighting oil," lubricating oil and wax from cannel coal and since 1862 from torbanite. In 1850 he patented the process of cracking oil.•Commercial scale shale oil extraction in Scotland started in 1859 by Robert Bell in Broxburn, West Lothian.

• It was not until 1859 that Amercians struck free-flowing oil.

• Oil shale was mined in the Lothian’s until 1962 but the industry died out because it could no longer compete with imported oil.

Crude oil and hydrocarbons

• Crude oil and its improved industrial extraction and processing produces a wide variety of energy-rich compounds called hydrocarbons.

• Crude oil – is a mixture of unprocessed hydrocarbons (of varying size/length)

• Hydrocarbons – are compounds that contain the element carbon and hydrogen.

Crude oil Hydrocarbons

Separated by their d

ifferent

Separated by their d

ifferent

boiling points

boiling points

How does fractional distillation work?

Forces between molecules

Fractional distillation

Combustion

In order to burn fuels require oxygen.Increasing the concentration of O2(g) increases the rate of burning.

The term ‘combustion’ is used to describe the process of burning (reaction with oxygen).

When combustion takes place the fuel reacts with oxygen in the air and energy is given out.

This means that combustion is an exothermic reaction.

HydrocarbonsHydrocarbons• Many of the fuels that we use are fossil

fuels.

• Fossil fuels were formed millions of years ago from material that was once living.

• There are three common fossil fuels - coal, oil and natural gas.

• The chemical compounds which are found in oil and natural gas are called hydrocarbons.

• These compounds are made up using

the elements hydrogen and carbon only.

Combustion of Combustion of HydrocarbonsHydrocarbons

• When hydrocarbons burn in a plentiful supply of oxygen, the products are carbon dioxide and water.

• This is complete combustion and the products will be the same for any hydrocarbon burning in a good supply of oxygen.

hydrocarbon oxygen carbon dioxide water

Products of CombustionProducts of Combustion

A burning hydrocarbon

is placed under the funnel

The first test tube

is surrounded by ice

The second test tube has lime

water

A pump is used to draw the gases through the apparatus

Tests for products

• Carbon dioxide turns limewater milky.

• Water boils at 100oC and freezes at 0oC. (or by using cobalt chloride paper which turns from blue to pink in the presence of water).

• The fact that water (hydrogen oxide) is produced proves that the fuel contains hydrogen. The fact that carbon dioxide is produced proves that the fuel contains carbon.

Quick Quiz

• Burns to release energy.

• Turns limewater cloudy.

• Burning with oxygen.

• A reaction that releases energy.

• 1:4

What is a fuel?

What is the test for carbon dioxide?

What is combustion?

What is an exothermic reaction?

What is the proportion of oxygen to nitrogen in the air?

Starter1. A mixture of ethanol (boiling point

79oC) and water is distilled. Which liquid will boil first?

2. What is a fraction?

3. Which are smaller, molecule in petrol or molecules in paraffin?

4. What is bitumen used for? 5. The hydrocarbon butane has the

molecular formula C4H10. In which fraction will butane be found?

Ethanol

A group of hydrocarbons with similar chemical properties and of a similar size

Paraffin

Roads and roofing

LPG (liquefied petroleum gas)

Aims:• Discuss the pollution problems

caused by the burning of hydrocarbons.

In the presence of oxygen, hydrocarbons burn to produce carbon dioxide and water.

Where does the carbon dioxide and water come from?

2 2CH4 + O2 CO2 + H2O

Carbon Dioxide• Carbon dioxide is a

greenhouse gas. • This means that it lets the

heat from the sun penetrate through to the earth, but doesn’t let it back out.

• The level of CO2 produced every year is increasing.

• Therefore the temperature of the earth is increasing.

• Effect is increased levels of seas/rivers causing flooding.

Carbon Monoxide• Hydrocarbons burned in insufficient

oxygen can produce carbon and carbon monoxide, which is a very poisonous gas.

• Carbon monoxide destroys blood’s ability to carry oxygen.

Sulphur Dioxide• Some fossil fuels contain small traces of

sulphur.• Sulphur dioxide is also a poisonous gas.• Sulphur dioxide can dissolve in rain to

produce acid rain.• Acid rain leads to corrosion of stonework

and metals.• Most SO2 is produced by coal and oil fired

power stations.• Removing sulphur compounds reduces air

pollution.

Nitrogen oxides•In car engines the air (N2 and O2) around the spark plug is provided with enough energy to cause a reaction between nitrogen and oxygen.

•Oxides of nitrogen are produced (NO2 and NO).

•NO2 dissolves in rain to produce nitric acid.

How Do We Overcome Pollution?

• Catalytic converters in car exhausts change harmful gases less harmful gases.

• E.g. CO CO2

NO and NO2 N2

– Catalytic converters contain transition metals (Pd, Rh or Pt on honey combed structures).

• Lean burn engines increase the ratio of air:fuel and so petrol is burned more efficiently. This causes a decrease in CO and unburned hydrocarbons.

• Leaded compounds have been removed from petrol to reduce pollution.

• Low-sulphur petrol produced.

• Sulphur dioxide removed from gases leaving power stations.

• Lime added to lakes to neutralise the effect of acid rain.

Quick Quiz1. Why does the production of carbon dioxide

and water on burning, indicate the presence of carbon and hydrogen in the original fuel?

2. What does ‘incomplete combustion’ mean?

3. Name a poisonous gas which can be produced as a result of incomplete combustion of petrol in a car engine.

4. Describe some of the effects of acid rain.

5. What does a catalytic converter do, and what type of material is it made from?

DistillationDistillation• This process is used to

separate substances due to them having different boiling points.

• E.g. water and alcohol can be separated using this process.

• Alcohol boils off first at 78oC and pure water is left behind.

Products from Crude OilProducts from Crude Oil

• Crude oil (petroleum) is a mixture of hydrocarbons.

• The hydrocarbons are separated into smaller mixtures (fractions) by a technique called fractional distillation.

• The hydrocarbons can be separated into different fractions using this process because they have different boiling points.

Uses and Properties of Uses and Properties of Fractions from Crude OilFractions from Crude Oil

Refinery gas

Gasoline (Petrol)

Kerosine

(Paraffin)

Gas Oils

(Diesel oil)

Residue

Fuel oil for ships / power stations / heating

Lubrication oils and waxes

Bitumen / tar for roads

Fuel gases

Fuel for cars

Aircraft fuel

Fuel for buses/taxis and cars.

Fraction

Chain length (no.of carbon atoms)

Uses Properties

Boiling pt. (oC)

Flammabillity

ViscosityEase of Evaporation

Refinery gas

1-4 Fuel gas <20

Petrol/ Gasoline (Naptha)

5-12Petrol and petrochemicals

20-180

Paraffin/ Kerosene

9-15Heating and fuel for aeroplanes

180-250

Diesel (Gas oil)

15-25Fuel for lorries/trains

250-350

Residue >25Lubricants, waxes, road tar

>350

DEC

REA

SES

INC

REA

SES

DEC

REA

SES

FractionsFractionsAT THE BOTTOM OF THE COLUMN

•Short carbon chains

•Light molecules •Heavy molecules

•Low boiling points •High boiling points

•Gases & very runny liquids •Thick, viscous liquids

•Very volatile •Low volatility

•Highly flammable •Not very flammable

•Light colour •Dark colour

AT THE TOP OF THE COLUMN

•Long carbon chains

Word BankWord Bank• Viscosity describes how well a liquid pours e.g.

treacle is very viscous, it is thick and pours very slowly. Large hydrocarbons are more viscous than small hydrocarbons.

• Flammability is how easily a substance will catch fire. Small hydrocarbons are more flammable than large hydrocarbons.

• Boiling point is a change of state from liquid to gas.

• Fraction is a group of hydrocarbons with boiling points within a given range.

Catalytic CrackingCatalytic CrackingChanging large hydrocarbons into

smaller more useful hydrocarbons.

e.g. C10H22 C8H18 + C2H4

During this type of reaction a smaller alkane (hydrocarbon) is always produced.

Catalyst

CatalystsCatalysts• A catalyst is a substance which:

– Increases rate of reaction– or– Allows a reaction to occur at a lower

temperature

N.B. A catalysts does not get used up during a chemical reaction. Therefore it is never included in a chemical reaction.

North Sea oil – How much left for Scotland/UK?

• Are there alternatives? And what are the pros and cons? Remember to analyse where your source information comes from [is it without bias?]

http://www.bbc.co.uk/news/uk-14432401

What is Fracking and why is it controversial?

Fracking in the news!

Alternatives in the news

•HydrocarbonHydrocarbon• familiesfamilies

Aims:

Discuss the Alkanes, which are a family of hydrocarbons.

The name for the first eight alkanes.

The structural formula of the first eight alkanes.

The molecular formula of the first eight alkanes.

The general formula for the alkane family.

HydrocarbonsHydrocarbons

• There are 3 hydrocarbon sub-groups:– Alkanes– Alkenes– Cycloalkanes

Same second name

Homologous series

Look similar

AlkanesAlkanes• Homologous series• Look similar• Contain covalent bonds.• All alkanes end in ‘ane’.• Remember each carbon must form 4

bonds. Each hydrogen must form 1 bond only.

Methane CH4

C H

H

H

H

C

H

CH

H

H

H

H

Ethane C2H6

Propane C3H8

C

H

CH

H

H

H

C

H

H

H

Methane

Ethane

Propane

Butane

Pentane

Hexane

Heptane

Octane

C

H

CH

H

H

H

H

C

H

CH

H

H

H

C

H

H

H

C

H

CH

H

H

H

C

H

C

H

H

H

H

C

H

CC

H

H

H

C

H

C

H

H

H

H

H

H

H

C

H

CC

H

H

H

C

H

C

H

H

H

H

H

C

H

H

H

H

C

H

CC

H

H

H

C

H

C

H

H

H

H

H

C

H

H

H

C

H

H

H

C

H

CC

H

H

H

C

H

C

H

H

H

H

H

C

H

H

H

C

H

H

C

H

H

H

C H

H

H

H CH4

C2H6

C3H8

C4H10

C5H12

C6H14

C7H16

C8H18

Molecular Formula

Full Structural Formula

Name of Alkane

Shortened Structural Formula

CH4

CH3CH2CH3

CH3CH3

CH3CH2CH2CH3

CH3CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH3

CH3CH2CH2CH2CH2CH2CH2CH3

• The molecular formula tells you the number of carbon and hydrogen atoms in each molecule.

• The full structural formula shows relative position of the atoms in the molecule and the bonds holding the atoms together.

• The shortened structural formula does not show all of the bonds in the molecule.

The alkanes are a homologous series. This means that:

1.All alkanes can be represented by a general formula which is:

2.They all have similar chemical properties

3.There is a link between their physical properties and their melting and boiling points.

CnH2n+2

Alkanes – Homologous series

The following rhyme might help you to remember the order of the hydrocarbons.

•MMonkeys

•EEat

•PPeanut

•BButter

•PPieces

•HHorses

•HHave

•OOats

Branched AlkanesBranched Alkanes• Branched: When not all of the carbon atoms

are in a straight chain.

C

H

H

H

C

H

H

C

H

H

H

C

H

H

H

C

H

H

H

C

H

H

C

H

H

H

C

H

H

CH

butane 2-methylpropane

Each molecule has:

Same molecular formula but a different structural formula

Different names

Naming Branched AlkanesNaming Branched Alkanes

Rules

1. Look for the longest carbon atom chain to give the name of the alkane.

2. Number the carbon atoms from the end closest to the branch.

3. Identify the branch- CH3 is a Methyl group C2H5 is an Ethyl group

4. Use prefixes to indicate how many of a particular branch (di-2, tri-3)

5. Show the position of each branch with a number placed in front of its name.

6. If more than one branch, names are put in alphabetical order (ethyl before methyl).

Example 1Example 1

Methyl branch

Number carbon atoms from one end closest to branch 2 Methyl butane

1 2 3 4

Example 2Example 2

C C C C C

C

C

C

1 3 642 5

Methyl branch

Ethyl branch

3 Ethyl, 2 Methyl hexane

Example 3Example 3Methyl branch

Methyl branch123

2,2-dimethyl propane

Drawing structures from Drawing structures from systematic namessystematic names

Example 1 3-methyl pentane

1 2 3 4 5

Example 2 4 ethyl, 2,2 dimethyl octane

C C C C C C C C

C

C

C

C

1 2 3 87654

Name the following structures

1.

2.

3.

4-ethyl-2-methylhexane

3-ethyl-4-methylhexane

4-ethyl-3,3-dimethylheptane

Draw the following structures

Draw a structural formula for each of the following alkanes

1. 3-ethylhexane

1. 2, 2, 4-trimethylpentane

1. 2-methyl, 3-ethylheptane

1. 4, 4-dimethyloctane

Lesson Starter1. State the bonding present in alkanes.

2. State the name of the third member of the alkanes.

3. State the molecular formula of the sixth member of the alkanes.

4. Draw the molecular structure of pentane.

5. State the general formula for the alkanes.

Same second name

Homologous series

Look similar

Aims:

Discuss the Alkenes, which are a family of hydrocarbons.

The name for alkenes up to C8.

The structural formula for the alkenes up to C8.

The molecular formula for the alkenes up to C8.

The general formula for the alkene family.

Ethene C2H4

Propene C3H6

The AlkenesThe Alkenes• The alkenes contain a carbon to carbon

double bond and so they are called unsaturated hydrocarbons.

• The names of all members end in ‘ene’.• The alkenes generally have lower melting and

boiling points than their equivalent alkanes. The smaller alkenes are gases, but as the molecules increase in size they become liquids and eventually solids.

• Their melting and boiling points also increase as we move from ethene hexene.

Name of Alkene

Molecular Formula

Full Structural Formula

Shortened Structural Formula

Ethene

Propene

Butene

Pentene

Hexene

C2H4

C3H6

C4H8

C5H10

C6H12

CH2=CH2

CH2=CHCH3

CH2=CHCH2CH

3

CH2=CHCH2CH2CH

3

CH2=CHCH2CH2CH2CH3

1. The alkenes can also be represented by a general formula which is:

2. They all have similar chemical properties3. There is a link between their physical

properties and their melting and boiling points.

CnH2n

Alkenes – Homologous series

Naming Straight Chain AlkenesNaming Straight Chain Alkenes

Rules1.Identify the longest carbon chain.2.Number carbon atoms starting at the

end nearest the double bond.3.Identify the number of the carbon atom

where the double bond starts, and insert it into the name.

ExamplesExamples1. 2.

3. 4.

But-1-ene But-2-ene

Hex-3-ene 2 MethylProp-1-ene

Starter1. What is the general formula of the

alkanes?

2. What is the general formula of the alkenes?

3. How can you distinguish between the alkanes and the alkenes?

4. What is the different between the bonding in these two families?

Aims:

1. Discuss the cycloalkane family.

2. Discuss isomers.

Homologous series

Look similar

Same first name

All ring structures

CycloalkanesCycloalkanes• The cycloalkanes are another series of

hydrocarbons.• The carbon atoms form a ring and all

carbon to carbon bonds are saturated (carbon to carbon single bonds).

Cyclopropane

C

C

C

HH

H

H

H

H

C3H6

Cyclobutane

C4H8C

C

C

C

H H

H

H

HH

H

H

Name of Cycloalkane

Molecular Formula

Full Structural Formula

Shortened Structural Formula

Cyclopropane

Cyclobutane

Cyclopentane

Cyclohexane

C3H6

C4H8

C5H10

C6H12

CH2

CH2

CH2

CH2

CH2

CH2CH2

CH2

CH2

CH2

CH2

CH2

CH2 CH2

CH2

CH2

CH2

CH2

Cycloalkanes – Homologous Cycloalkanes – Homologous seriesseries1.All alkanes can be represented by a

general formula which is:

2.They all have similar chemical properties

3.There is a link between their physical properties and their melting and boiling points.

CnH2n

Isomers-Same molecular formula but

different structural formula.

e.g. C3H6 is the molecular formula for … Propene Cyclopropane

and

C

C

C

HH

H

H

H

H

Butene and cyclobutane are isomers because they both have the molecular formula C4H8 but their structures are different.

There are two isomers of butane, both with the molecular formula C4H10.

Butane 2-methylpropane

The larger the hydrocarbon, the more isomers are possible.

Can you try to draw 3 isomers for pentane?

Quick Quiz

1. What is the molecular formula for

cyclopentane?

2. Draw the structure of cyclobutane.

3. What is an isomer?

4. Draw three isomers of pentane.

Starter1. Name the 6th member of the alkanes.2. Name the 1st member of the alkenes.3. Name the 2nd member of the

cycloalkanes.4. What is the general formula for the

cycloalkanes?5. What bonding is present in the

cycloalkanes?6. What is a homologous series?

Saturated or UnsaturatedSaturated or Unsaturated• Saturated hydrocarbon: • a hydrocarbon that contains carbon to

carbon single covalent bonds only. • Alkanes and cycloalkanes are saturated

compounds

• Unsaturated hydrocarbon: • a hydrocarbon that contains at least one

carbon to carbon double covalent bond.• Alkenes are unsaturated compounds

Testing for UnsaturationTesting for Unsaturation

• Bromine water is used in order to determine whether an unknown hydrocarbon is saturated or unsaturated.

• Saturated hydrocarbons will have no effect on bromine water.

Unsaturated hydrocarbons rapidly turn orange/brown bromine water colourless.

Addition ReactionsAddition Reactions

• A C=C is very reactive and will easily break to give a carbon-to-carbon single covalent bond.

When Addition occurs…

alkene + hydrogen alkanee.g.

ethene + hydrogen ethane

+ H2 C

H

CH

H

H

H

H

Carbon to carbon double bond breaks. Bond between hydrogen molecule breaks and H atoms will join across the double bond.

Butene + H2 Butane

+ H2 C

H

CH

H

H

H

C

H

C

H

H

H

H

Addition of hydrogen is also called hydrogenation.

Addition of bromine - Bromination

1,2 dibromopropane (saturated)

The bromine molecule adds on across the double bond to give a Br atom on each atom either side of where the double bond used to be.

Addition of Water - Addition of Water - HydrationHydration

Adding water to an alkene gives the corresponding alcohol.

Alkene + water Alcohol

H-OH (H2O)

Making Plastics

• The most important use of alkenes and alkene derivatives is as feed stocks for the plastics industry…This is dealt with in Unit 3 (additional polymerisation)…so we will leave it till.

Everyday consumer products

•Energy from fuels

•Alcohols

•Carboxylic acids

•Esters

Contents

AlkanolsAlkanols(Alcohols)(Alcohols)

Alcohols• Look like alkanes but contain a hydroxyl

(OH) group.• names similar to alkanes but ending in

‘OL’, and each contains the hydroxyl group, OH, in place of a hydrogen atom.

e.g. second alcohol is ethanol (C2H5OH)

Shortened structural formula: CH3CH2OH

Name of alkanol

Molecular formula

Full structural Formula

Shortened structural formula

Methanol

Ethanol

Propanol

Butanol

Pentanol

Hexanol

Heptanol

Octanol

CH3OH

C2H5OH

C3H7OH

C4H9OH

C5H11OH

C6H13OH

C7H15OH

C8H17OH

CH3OH

CH3CH2OH

CH3CH2CH2OH

CH3CH2CH2CH2OH

CH3CH2CH2CH2CH2OH

CH3CH2CH2CH2CH2CH2OH

CH3CH2CH2CH2CH2CH2CH2OH

CH3CH2CH2CH2CH2CH2CH2CH2OH

Naming AlkanolsNaming AlkanolsRules1. Longest chain containing OH gives

alkane name (replace e with ol)2. Number carbon atoms in the chain

start from the end closest to the OH.3. For chains of 3 or more carbons name

the position of the OH must be given.4. Any branches must be named and

numbered.

Propan-2-ol

Dehydration of AlkanolsDehydration= removal of water

Alcohol equivalent Alkene + water

Butan-1-ol But-1-ene + water

O

HH+

Alkanoic AcidsAlkanoic Acids

• They look like alkanes but contain a carboxyl (COOH) group.

• Same names as alkanes but end in “oic”.

e.g. first alkanoic acid is METHANOIC ACID.

e.g. Full structural formula

HCOOH

Or

HCO2H

Shortened structural formula

Carboxyl functional group

Name of alkanoic acid

Molecular formula

Full structural formula

Shortened structural formula

Methanoic acid

HCOOH

Ethanoic acid

CH3COOH

Propanoic acid

C2H5COOH

Butanoic acid

C3H7COOH

HCOOH

CH3COOH

CH3CH2COOH

CH3CH2CH2COOH or

CH3(CH2)2COOH

Name of alkanoic acid

Molecular formula

Full structural formula

Shortened structural formula

Pentanoic acid

C4H9COOH

Hexanoic acid

C5H11COOH

Heptanoic acid

C6H13COOH

Octanoic acid

C7H15COOH

CH3-(CH2)3-COOH

CH3-(CH2)4-COOH

CH3-(CH2)5-COOH

CH3-(CH2)6-COOH

Naming Alkanoic AcidsNaming Alkanoic Acids

Rules1.Count the number of atoms in the

carbon chain to give the name of the parent alkanol.

2. Remove the –ol ending of the parent alkanol and replace it by –oic acid.

Esters

EstersAre covalent compounds that contain

carbon, hydrogen and oxygen.

Have a characteristic smells (e.g. pear

drops)

Are insoluble in water.

names end in –OATE and contain the ester

linkage –COO-, shown below.

O

CO

Formation of estersFormation of esters

Esters are the products of reactions

between carboxylic acids (alkanoic acids)

and alcohols (alkanols).

The alkanol loses an –H and the

alkanoic acid loses the –OH group.

molecules join together to form an ester

molecule with a water molecule.

the reaction between ethanoic acid and methanol can be represented as

shown:

methanol

(alkanol)

ethanoic acid

(alkanoic acid)

C H 3 C

O

O H H O C H 3

C H 3 C

O

O C H 3

+ H2O

ester

Ester link

Ethanoic Acid

Water

Ethanol

Ethyl Ethanoate

Ester link

Naming Esters

1. The names for esters are based on the alkanol and alkanoic acid from which they are made.

2. Esters names are usually written as two words of the type alkyl alkanoate.

3. The first part of the name comes from the alkanol with the –ol ending removed and –yl added.

4. The second part of the name comes from the alkanoic acid with the –oic acid ending changed to –oate.

Alkanol Alkanoic acid Name of ester

Methanol Methanoic acid Methyl methanoate

Ethanol Methanoic acid Ethyl methanoate

Methanol Ethanoic acid Methyl ethanoate

Ethanol Ethanoic acid Ethyl ethanoate

Methanol Propanoic acid Methyl propanoate

Ethanol Propanoic acid Ethyl propanoate

Reactions of Carbon Reactions of Carbon CompoundsCompounds

Many hydrocarbons take part in chemical reactions.

We have already discussed 1-31. Addition2. Cracking3. Production of Ethanol 4. Making and Breaking Esters

Making and Breaking Esters

Making EstersMaking Esters

• Esters are made by a condensation reaction between carboxylic acid and an alcohol.

• This can also be called an esterification reaction.

• In this reaction a water molecule is eliminated from the functional groups of the carboxylic acid (COOH) and alcohol (OH).

An ester link is formed by the reaction of the hydroxyl (OH) functional group and the carboxyl (COOH) functional group.

CH3 C

O

OH CH3OH

CH3 C

O

O CH3

H OH

+

+

Ester link

• Condensation reaction is slow at room temperature and yield of the ester is low.

• Rate can be increased by heating reaction mixture and by using concentrated sulphuric acid as a catalyst.

• Evidence that an ester is formed is its typical sweet smell, and that is appears as a solid/oily liquid on the water.

• The process is reversible i.e it operates in both directions. This means it is possible to break the ester down to the alkanol and alkanoic acid that made it.

Breaking EstersBreaking Esters

• An ester can be broken down into its parent alcohol and carboxylic acid.

• This involves heating the ester with water and so it is called a hydrolysis reaction.

• Hydrolysis reactions are the reverse of condensation reactions.

• This is also a reversible reaction.

Remember...Remember...

• Condensation reaction makes an ester

and water is formed.

• Hydrolysis reaction breaks an ester and

water is used up.

• These are reverse reactions.