Organic chemistry

What are hydrocarbons?

A hydrocarbon is a compound that contains only hydrogen and cabron atoms

The empirical formula shows the ___________________ of the atoms in a molecule

simplest possible ratio

The molecular formula shows the ______________ of atoms in a molecule

actual number

What is a homologous series

A homologous series is a series or family of organic compounds that have similiar features and chemical properties due to them having the same functional group.

All members of a homologous series have:

• The same general formula

• Same functional group

• Similar chemical properties

• Gradation in their physical properties

• The difference in the molecular formula between one member and the next is CH₂

All members of a homologous series have the ____ general formula

same

All members of a homologous series have _____ functional group

same

All members of a homologous series have _________ chemical properties

similiar

All members of a homologous series have __________ in their physical properties

Gradation

In all members of a homologous, the difference in the molecular formula between one member and the next is ____

CH₂

What is a functional group?

A group of atoms bonded in a specific arrangement that influences the properties of the homologous series

What are isomers?

Isomers are compounds that have the same molecular formula but different displayed formulae

The reactions of organic compounds can be classified into:-

• Substitution

• Addition

• Combustion

What is a susbtitution reaction?

A substitution reaction takes place when one functional group is replaced by another

What provides the activation energy for subsitution reactions in organic compounds?

Ultraviolet light

What is the purpose of Ultraviolet light in substitution reaction

Ultraviolet light provides the activation energy needed to start the substitution reaction.

Reaction of methane and bromine

CH₄    +    Br₂       →            CH₃Br   +    HBr

    methane + bromine   →   bromomethane + hydrogen bromide

Reaction of ethane and bromine

Ethane + Bromine → Bromoethane + Hydrogen bromide
C₂H₆ + Br₂ → C₂H₅Br + HBr

Reaction of Propane and bromine

Propane + Bromine → Bromopropane + Hydrogen bromide
C₃H₈ + Br₂ → C₃H₇Br + HBr

Reaction of butane and bromine

Butane + Bromine → Bromobutane + Hydrogen bromide
C₄H₁₀ + Br₂ → C₄H₉Br + HBr

Reaction of pentane and bromine

Pentane + Bromine → Bromopentane + Hydrogen bromide
C₅H₁₂ + Br₂ → C₅H₁₁Br + HBr

Reaction of hexane with bromine

Hexane + Bromine → Bromohexane + Hydrogen bromide
C₆H₁₄ + Br₂ → C₆H₁₃Br + HBr

Reaction of methane and chlorine

CH4​+Cl2​→CH3​Cl+HCl

• methane + chlorine → chloromethane + hydrogen chloride

When an alkane reacts with a halogen what happens?

a substitution reaction

When an alkene reacts with a halogen what happens?

addition reaction

What is an addition reaction?

An addition reaction takes place when two or more molecules combine to form a larger molecule with no other products

Reaction of ethene and bromine

Ethene + Bromine → 1,2-dibromoethane
C₂H₄ + Br₂ → C₂H₄Br₂

Reaction of propene and bromine

Propene + Bromine → 1,2-dibromopropane
C₃H₆ + Br₂ → C₃H₆Br₂

Reaction of butene with bromine

Butene + Bromine → 1,2-dibromobutane
C₄H₈ + Br₂ → C₄H₈Br₂

Reaction of Pentene with bromine

Pentene + Bromine → 1,2-dibromopentane
C₅H₁₀ + Br₂ → C₅H₁₀Br₂

Reaction of hexene with bromine

Hexene + Bromine → 1,2-dibromohexane
C₆H₁₂ + Br₂ → C₆H₁₂Br₂

Reaction of ethene and chlorine

C₂H₄ + Cl₂ → C₂H₄Cl₂
Ethene + Chlorine → 1,2-dichloroethane

What is the scientific term for burning?

combustion

What is combustion?

In a combustion reaction, an organic substance reacts with oxygen to form carbon dioxide (or carbon monoxide if incomplete combustion) and water.

What is complete combustion?

Complete combustion is when a hydrocarbon burns in an unlimited supply of oxygen.
It produces carbon dioxide and water.

What is incomplete combustion?

Incomplete combustion is when a hydrocarbon burns in a limited supply of oxygen.
It produces carbon monoxide and water.

Reaction in complete combustion

CH₄   +   2O₂   →   CO₂   +   2H₂O

C₃H₈   +   5O₂   →   3CO₂   +   4H₂O

Reaction in incomplete combustion

CH₄   +   ^3/2O₂   →   CO   +   2H₂O

Each fraction consists of groups of hydrocarbons of ________ chain lengths

similiar

The fractions in petroleum are separated from each other in a process called ____________ ______________

fractional distillation

The molecules in each fraction have similar ____________ and _______________

properties and boiling points

The ____________________ of each hydrocarbon molecule determines in which fraction it will be separated into

size and length

Most fractions contain mainly _______

alkanes

Fractional distillation is carried out in a _______________ _______ which has a temperature gradient 

fractionating column

What do you mean by a temperature gradient?

• It is very hot at the bottom of the column and cooler at the top

What happens in the process of fractional distillation?

• During the process of fractional distillation:

  • The crude oil is heated and vapourises

  • The vapours of hydrocarbons enter the column which has a temperature gradient

  • The vapours of hydrocarbons with high boiling points condense at the bottom of the column

  • The vapours of hydrocarbons with lower boiling points rise up the column and condense at the top 

What is vicoscity?

This refers to the ease of flow of a liquid

How do high viscosity liquids flow

flow less easily

What happens to the viscosity when the number of carbon atoms/ mass increase?

the attraction between the hydrocarbon molecules also increases which results in the liquid becoming more viscous with the increasing length of the hydrocarbon chain

What happens to the colour when the number of carbon atoms/ mass increase?

• As carbon chain length increases the colour of the liquid gets darker as it gets thicker and more viscous

What happens to the Melting point/boiling point when the number of carbon atoms/ mass increase?

• As the molecules get larger, the intermolecular attraction becomes greater

• So more heat is needed to separate the molecules

• With increasing molecular size there is an increase in boiling point

What happens to the Volatility when the number of carbon atoms/ mass increase?

• Volatility refers to the tendency of a substance to vaporise

• With increasing molecular size hydrocarbon liquids become less volatile

• This is because the attraction between the molecules increases with increasing molecular size

What is volitality?

• Volatility refers to the tendency of a substance to vaporise

What is the use of Liquified petroleum gas?

Domestic heating & cooking

What is the use of Petrol?

Fuel for cars (gasoline)

What is the use of Kerosene?

Jet fuel (paraffin)

What is the use of Diesel?

Diesel engines (gas oil)

What is the use of heavy fuel oil?

Ships & power stations

What is the use of bitumen?

Surfacing roads and roofs

What is a fuel?

• A fuel is a substance that, when burned, releases heat energy (exothermic reaction)

What are some fossil fuels>

• Fossil fuels include: coal, oil, natural gas, oil shales and tar sands

• Non-renewable fossil fuels are obtained from ______ ___ by fractional distillation

What is petrol used for?

Petrol is used as a fuel in cars

Where is coal use?

• Coal is used in power stations and also steel production

Natural gas consists mainly of _______, ___

methane, CH₄

All these fuels contain ______, _________ and small quantities of ______

carbon, hydrogen and sulfur

The burning of fossil fuels releases the gases :-

• carbon dioxide, carbon monoxide, oxides of nitrogen and oxides of sulfur

The burning of fuels also other than gas gives rise to

unburned hydrocarbons and carbon particulates

When the fuel is a hydrocarbon then _____ and _______ _______ are the products formed

water and cabron dioxide

Complete combustion occurs when there is _______ ______

excess oxygen

Incomplete combustion occurs when there is _________ _________ to burn

insufficient oxygen

In which appliance does incomplete combustion occur

It occurs in some appliances such as boilers and stoves as well as in internal combustion engines

What are the products of incomplete combustion?

• The products of these reactions are unburnt fuel (soot), carbon monoxide and water

Why is carbon monoxide dangeorus?

Carbon monoxide is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death

• The CO binds well to haemoglobin which therefore cannot bind oxygen

• Oxygen is transported to organs

How are nitrogen oxides formed?

These compounds (NO and NO₂) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces

Why are catlytic converters fit inside parts of exhaust system?

Catalytic converters reduce harmful gases in car exhausts by using a catalyst to speed up reactions. They convert carbon monoxide and unburned hydrocarbons into less harmful substances, and they also remove nitrogen oxides by breaking them down into nitrogen and oxygen.

What is the function of a catlytic converter?

Their function is to render these exhaust gases harmless

What are effects of nitrogen oxides?

• acid rain

• photochemical smog breathing

• difficulties, in particular for people suffering from asthma.

Fossil fuels are often contaminated with small amounts of _______ __________

sulfur impurities

When these contaminated fossil fuels are combusted, the sulfur in the fuels get ___________ to ______ ______

oxidised to sulfur dioxide

Reaction of sulfur being oxidised

 S (s) + O₂ (g) → SO₂ (g)

What are the effects of sulfur dioxide?

• The adverse effects of sulfur dioxide include acid rain:

  • Acid rain causes corrosion to metal structures, buildings and statues made of carbonate rocks, damage to aquatic organisms

  • It pollutes crops and water supplies, irritates lungs, throats and eyes

How is acid rain formed from sulfure dioxide?

• The sulfur dioxide produced from the combustion of fossil fuels dissolves in rainwater droplets to form sulfuric acid

2SO₂ (g) + O₂ (g) + 2H₂O (l) → 2H₂SO₄ (aq)

• Sulfuric acid is one of the components of acid rain which has several damaging impacts on the environment

How is acid rain formed from nitrogen dioxide

• Nitrogen dioxide produced from car engines reacts with rain water to form a mixture of nitrous and nitric acids, which contribute to acid rain:

2NO₂ (g) + H₂O (l)  → HNO₂ (aq) + HNO₃ (aq)

• Lightning strikes can also trigger the formation of nitrogen monoxide and nitrogen dioxides in air

• Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid

4NO₂ (g) + 2H₂O (l) + O₂ (g)→ 4HNO₃ (aq)

• When the clouds rise, the temperature decreases, and the droplets get larger

• When the droplets containing these acids are heavy enough, they will fall down as acid rain

What is cracking?

Cracking is an industrial process used to break low demand, long chain hydrocarbon molecules into more useful, small chain hydrocarbon molecules

What are the conditions for catlytic cracking?

• Catalytic cracking involves heating the hydrocarbon molecules to around 600 – 700 °C to vaporise them

• The vapours then pass over a hot powdered catalyst of aluminium oxide

• This process breaks covalent bonds in the molecules as they come into contact with the surface of the catalyst, causing thermal decomposition reactions

Alkanes are a group of __________ hydrocarbons

saturated

The general formula of the alkanes is __________

C_nH_2n+2

Alkanes are generally ___________ compounds

unreactive

What are the alkanes

Methane

Ethane

Propane

Butane

Pentane

What is the empirical and molecular formula of methane?

CH₄, CH₄

What is the molecular and empirical formula of ethane?

Molecular formula:

C₂H₆

Empirical formula:

CH₃

What is the molecular and empirical formula of propane

Molecular formula:

C₃H₈

Empirical formula:

C₃H₈

What is the molecular and empirical formula of butane?

Molecular formula:

C₄H₁₀

Empirical formula:

C₂H₅

What is the molecular and empirical formula of pentane?

Molecular formula:

C₅H₁₂

Empirical formula:

C₅H₁₂

Displayed equation for CH₄ + bromine

What are the products of halogen + alkene substitution reaction called?

• The products belong to a family called halogenoalkanes or haloalkanes

What are the uses of halogenoalkanes or haloalkanes?

• Halogenoalkanes have many uses a solvents, refrigerants, propellants and pharmaceuticals

Alkenes are ___________ hydrocarbons

unsaturated

What is the general formula for alkenes?

The general formula of an alkene is C_nH_2n