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Learning Objectives • State that petroleum (or crude oil) and natural gas (mainly methane) are important sources of energy. • Describe petroleum as a mixture of hydrocarbons and it can be separated into its various fractions via fractional distillation. • State that hydrocarbons are compounds that are made up of hydrogen and carbon. • Describe the order and uses of the various fractions of petroleum.

What is Organic Chemistry?

Organic Compounds in Our Daily Life

carbon Organic chemistry refers to the study of _________ compounds ____________. Carbon is able to form a large number of compounds covalent bonds with other because it forms stable ___________ atoms.

Glucose (C6H12O6)

methane

petroleum (or Organic compounds are made from ____________ natural gas crude oil) and ________________.

hydrocarbons which are Petroleum and natural gas are ______________ hydrogen carbon and __________. compounds made up only of _________

Natural Gas methane Natural gas consists mainly of ____________.

It is used for heating and cooking. Petroleum and natural gas are our main source of energy. Combustion of Petroleum and natural gas: hydrocarbon  O 2  CO 2  water  heat energy Main products

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Petroleum

What happens in an oil refinery?

 Petroleum (or crude oil) is a dark brown, foul-smelling liquid.

3. Hot vapour rises up the column and begins to cool down.

 Petroleum (or crude oil) is a complex mixture of hydrocarbons.

The smaller hydrocarbons are collected at the top of the fractionating column as gases.

7 fractions in oil refineries.  Petroleum can be separated into ____________

The bigger hydrocarbons are collected at the lower sections of the fractionating column.

 The process to separate petroleum into various fractions is called fractional distillation ________________________.

fractionating column is used to separate petroleum  A _________________________ into various fractions.

What happens in an oil refinery?

2. The vapour is pumped into a huge fractionating column. 1. In the furnace at the bottom of the fractionating column, petroleum is heated into a vapour.

Uses of Petroleum Fractions Fractions

Boiling Range (C)

# carbon atoms per molecule

Uses

Petroleum gas

Below 40

1– 4

Fuel for cooking and heating

Petrol (gasoline)

40 – 75

5 – 10

Fuel for car engines

Naphtha

75 – 150

7 – 14

Feedstock (raw material) for petrolchemical industry (which produces plastics, detergents, etc)

Kerosene (paraffin)

160 – 250

11 – 16

Fuel for aircraft engines; for cooking using oil stoves; for heating purposes

This fraction has the highest range of boiling points.

Diesel oil

250 – 300

16 – 20

Fuel for diesel engines

Lubricating oil

300 – 350

20 – 35

For lubricating machines; for making waxes and polishes

It is the residue at the bottom of the fractionating column.

Bitumen (asphalt/residue)

Above 350

More than 70

For paving road surfaces

This fraction has the lowest range of boiling points and is distilled over first. Petroleum gas is a mixture of gases including methane, propane and butane.

Alternative Fuels To conserve fuels, we should use these fuels carefully and consider using alternative sources of energy. One possible source of fuel comes from plants such as palm oil.

Another important fuel is biogas. It is the gas produced when organic matter (waste material from plants or animals) is allowed to decay in the absence of air. Biogas contains about 50% methane.

Alcohol produced from sugarcane mixed with petrol can be used to run vehicle engines.

The Oil Refining Industry in Singapore Although Singapore is a country with limited natural resources, it is the world’s third largest oil-refining centre and a major refining centre for Southeast Asia. The refineries here refine nearly twice the amount of petroleum consumed in Singapore. The rest of the petroleum is exported to different parts of the world. There are also two industrial plants on Jurong Island, which produce petrochemicals from naphtha fractions.

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Learning Objectives General Introduction to Organic Compounds

Describe homologous series as a family of compounds with similar chemical properties and functional group.  Describe the general characteristics that will be observed for a homologous series. State the name of organic compounds by combining the prefix (number of carbon atoms) and the suffix (homologous series).

Classification of Organic Compounds

Homologous Series - Alkanes

A homologous series is a family of organic compounds with similar chemical properties. Compounds in the same homologous series have the same functional groups. Functional group is an atom or a group of atoms that gives a molecules its characteristic properties. Propane

Homologous Series - Alkenes

General Characteristics of Homologous Series Organic compounds in the same homologous series have the following properties in common:

a) They have the same functional group. b) They have similar chemical properties. c) There is a gradual change in their physical properties. Propene

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Naming Organic Compounds Part 1

Naming Organic Compounds Part 2

The PREFIX tells us the number of carbon atoms in each molecule.

The SUFFIX tells us the homologous series of the compound.

First part of the name

Number of carbon atoms in each molecule

Name of ending

Homologous Series

Meth-

1

-ane

Alkane

Eth-

2

-ene

Alkene

Prop-

3

-ol

Alcohol

But-

4

-oic acid

Carboxylic acid

Naming Organic Compounds • Propene is an alkene with 3 carbon atoms per molecule.

Organic Chemistry: Alkanes

Methane

Learning Objectives

Alkanes

Describe alkane as a homologous series of saturated hydrocarbons with the general formula of C nH2n+2

Alkanes are hydrocarbons that contain only single covalent bonds between the carbon atoms.

Draw the full structure of straight chain alkanes C 1 to C3 and name them.

They are known as saturated hydrocarbons because of the C-C single bond.

Describe the general trend in physical properties of alkanes.

Alkanes have general chemical formula of CnH2n+2 where n represents the number of carbon atom.

Describe the substitution reaction of alkane with halogen.

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Full Structural Formula of C1 to C3 Alkanes

First 5 members of alkane homologous series Name

# carbon atom

Molecular formula

Melting Point

Boiling point

Physical state (r.t.p.)

Methane

1

CH4

-182

-162

Gas

Ethane

2

C 2H 6

-183

-89

Gas

Propane

3

C 3H 8

-188

-42

Gas

Butane

4

C4H10

-138

-0.5

Gas

Pentane

5

C5H12

-130

36

Liquid

Properties of Alkanes Property 1: Melting and boiling point The melting point and boiling point of alkanes increases as the molecular sizes increases.

• The full structural formula shows all the bonds between the atoms in a molecule. This allows us to see the arrangement of the atoms in a molecule.

Properties of Alkanes Property 2: Density The density of alkanes increases as their molecular sizes increases.

Explanation: As alkane molecules get bigger, the attractive force between the molecules become stronger. More energy is needed to overcome the attractive forces.

Properties of Alkanes Property 3: Viscosity Definition of viscosity: the flowability of liquid. More viscous  difficult to flow The viscosity of alkane increases (more difficult to flow) as their molecular size increases. Explanation: The intermolecular forces get stronger as the molecular sizes increases, thus, making it more difficult to flow.

Properties of Alkanes Property 4: Flammability

As the molecular size of alkane increases, there is an increases in the number of carbon in the molecules. This makes alkanes less flammable (more difficult to burn). As the molecular size of the alkane molecules increases, the percentage of carbon in the alkane molecules also increases. Produce a smokier flame, which is caused by incomplete combustion of alkane molecules.

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Properties of Alkanes Property 5: Combustion Alkanes burn readily in air when ignited by a spark or flame to produce CO2 (g) and H2O (g).

Chemical Properties: Substitution Reaction Generally, alkanes are unreactive. Why? Alkanes are saturated hydrocarbons with single carbon-carbon (C–C) bonds and carbon-hydrogen (C–H) bonds. These bonds are strong and are difficult to break.

Equation of combustion (for example Methane):

However, alkanes reacts with halogens (group 7 elements) in the presence of UV (Ultraviolet) light.  substitution reaction.

Complete combustion Incomplete combustion

Chemical Properties: Substitution Reactions In substitution reaction, the halogen atom will replace one of the hydrogen atom in the alkane. More hydrogen atoms can be replaced by halogen atom to form a mixture of products. The reaction continues until all the hydrogen atoms are replaced by chlorine atoms.

Chemical Properties: Substitution Reactions

Chemical Reaction: Cracking Alkanes with long carbon chains are usually not used in fuels because they are less flammable. So how can we use these alkanes? Solution: We can break alkanes with long carbon chains into smaller molecules through cracking process.

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Learning Objectives Organic Chemistry: Alkenes

Describe alkenes as a homologous series of unsaturated hydrocarbons with the general formula of CnH2n Draw the full structure of straight chain alkanes C2 and C3 and name them. Describe the general trend in physical properties of alkanes.

Alkenes  Alkenes are hydrocarbons that contain one or more carbon-carbon double bonds between the carbon atoms.

 They are known as unsaturated hydrocarbons because of the C-C double bond.

First 3 members of Alkenes Name

# carbon atom

Molecular formula

Boiling point

Physical state (r.t.p.)

Ethene

2

C 2H 4

-104

Gas

Propene

3

C 3H 6

-48

Gas

Butene

4

C 4H 8

-6

Gas

Functional group of alkenes

 Alkanes have general chemical formula of CnH2n where n represents the number of carbon atom.

Structure of Alkenes

An alkene differs from the previous one by an additional –CH2– unit.

Structure of Alkenes

The first 3 members of the alkene homologous series...

The first member of alkene is ethene, not methene.

Each alkene differs from the next by a –CH2 – unit.

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Full Structural formula of Ethene and Propene

Structure of Alkenes

Name: Ethene

Name: Propene

Molecular formula: C2H4

Molecular formula: C3H6

The first few alkenes are gases. Boiling point increases as the alkene size increases.

Functional group: C-C double bond

Please note that there must only be 4 bonds connecting to each carbon atom.

Combustion •

Chemical Properties of Alkenes

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

•

Addition Reactions

Similar to alkanes, Alkenes burn in oxygen to produce CO2 and H2O.

There is a higher percentage of carbon in alkenes compared to alkanes, alkenes burn with a smokier flame than alkanes with a similar number of carbon atoms.

3 Addition Reactions

•

The C-C double bonds in alkenes are very reactive, thus it readily combines with other substance to form a saturated organic compound.

1. Hydrogenation — addition of hydrogen to alkenes

•

The C-C double bond will become single bonds in this reaction.

2. Bromination — addition of bromine to alkenes

•

General equation of addition reaction:

+

3. Hydration — addition of steam to alkenes

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Hydrogenation – Addition of Hydrogen to Alkenes At 200 °C and in the presence of a catalyst such as nickel, alkenes can react with hydrogen to form alkanes. For example when ethene reacts with hydrogen,

+

Application of Hydrogenation • Hydrogenation is used in the production of margarine. • Hydrogen is added to vegetable oil (in the presence of nickel catalyst and temperature of 200° C) to produce margarine. • The greater the amount of hydrogen added, the more solid is the margarine.

Bromination – Addition of Bromine to Alkenes

Bromination – Addition of Bromine to Alkenes

• When alkene (unsaturated hydrocarbon) is added to bromine solution, it will immediately decolourises reddishbrown bromine to a colourless oil.

We can use bromination to test for the presence of an alkene or unsaturation.

.

For example when ethene reacts with bromine,

+

Bromination

If an alkene is present, bromine solution will be rapidly decolourised.

Hydration – Addition of Steam to Alkenes Ethene can react with steam to produce ethanol. Conditions: catalyst (phosphoric(V) acid), 300 °C and 60 atm

+

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Manufacturing Alkenes by Cracking Alkenes are obtained by cracking petroleum (crude oil). Cracking is the breaking down of long-chain hydrocarbons into smaller molecules.

Cracking – Conditions and Products Cracking is done by passing the petroleum fraction (long chains of carbon atoms) over a catalyst (aluminium oxide or silicon(IV) oxide) at a high temperature (about 600 °C).

Here, hexane is cracked to produce butane and ethene.

Cracking of Alkenes in School Lab Petroleum vapour is passed over a heated porous pot. The porous pot contains the catalysts. The product is a mixture of alkanes and alkenes especially ethene.

3 possible products

Why is cracking important? Cracking is used to produce… 1. petrol 2. short-chain alkenes 3. hydrogen

1. Cracking is used to produce petrol. Our need for petrol is greater than our need for diesel oil or lubricating oil.

2. Cracking is used to produce short-chain alkenes. Short-chain alkenes such as ethene and propene are used as starting materials for making ethanol and plastics.

Through cracking, diesel oil or lubricating oil can be converted into petrol.

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3. Cracking is used to produce hydrogen.

Comparing Alkanes and Alkenes Similarities 1. both alkanes and alkenes are compounds that contains only hydrogen and carbon. Both alkanes and alkenes are flammable. On complete combustion, they produce CO2 and H2O.

Hydrogen is a by-product in the cracking of alkanes.

Comparing Alkanes and Alkenes Differences Properties

Alkanes

Alkenes

Molecular structure

Contains C-C single bonds

Contains C-C double bonds

Reactivity

unreactive

Very reactive (due to CC double bonds)

Types of reactions

Substitution reaction (with halogen)

Addition reaction

Reaction with aqueous bromine

Do not react with bromine

Decolourise aqueous bromine immediately

Combustion (of alkane and alkene containing same number of carbon atoms)

Produce less smoky flame

Produce smokier flame

Quick Check • Read through the following sentences and circle true or false. 1.

The physical properties of a homologous series change gradually as the number of carbon atoms increase.

True/False

2. The simplest alkene molecules has one carbon atom.

True/False

3. Alkenes but not alkanes undergo addition reactions.

True/False

4. Bromine solution can be used to distinguish alkanes from alkenes.

True/False

5. In the cracking of large alkane molecules, one product is always an alkene.

True/False

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