GCSE Chemistry: Organic Chemistry (T7)

What is crude oil?

Crude oil is a finite (non-renewable) resource found in rocks.

• its remains of ancient biomass → mainly plankton that was buried in mud.

• Mixture of hydrocarbons → mainly alkenes

What is crude oil used for?

Plastics (polymers)

Fuels :

• petrol → cars

• Diesel → buses , Lorrie’s

• Kerosene → aircraft

• Heavy fuel oil→ships , power stations

• Liquified petroleum gas (LPG) →heating & cooking gas

Cosmetics

Pharmaceuticals

How is crude oil formed?

Crude oil is formed over millions of years from the remains of tiny sea creatures called plankton which were buried in mud and sediment

These organisms die,sink to the ocean floor and are gradually covered by layers of sediment

over millions of years→ due to high pressure and temperature of overlying layers causes organic biomass to transform into crude oil.

Why’s it important?

Society relies heavily on it for both energy and materials→ scientists researching alternative fuels and recycling plastics

What is a hydrocarbon?

Molecules made up of hydrogen and carbon atoms only.

What is an alkane ?

Saturated hydrocarbons, meaning they contain only single bonds between carbon atoms. And maximum number of hydrogen atoms possible

What is the general formula for alkanes?

CnH2n+2

• if know num. of carbon atoms in the alkane (n) →can calculate the number of hydrogen atoms

• To do that → multiply num of carbon atoms by 2 & then +2

What are the first 4 alkanes ?

• methane

• Ethane

• Propane

• Butane

What are the 3 properties of a hydrocarbon?

• Viscosity → tells us the thickness of a fluid→As size of hydrocarbon molecules increase → molecules get more vicious

• Flammability → how easily a hydrocarbon combusts (burns)→as size of hydrocarbon increases →molecules get less flammable

• Boiling point →the temp. At which a liquid turns to a gas →size of hydrocarbons molecules increases the boiling point increases

Describe the properties of long chained hydrocarbons.

• have a high viscosity → flow slowly

• aren’t very flammable-.hard to burn

• have high boiling points and melting points.

• Not volatile

Describe the properties of short chained hydrocarbons.

• They have low viscosity

• They are highly flammable

• They have low boiling points

• They are volatile

Describe complete combustion of hydrocarbons

• Combustion = chemical reaction where a substance burns in oxygen to release enegy

• Complete combustion = Hydrocarbons (e.g alkenes) burns fully in plenty of oxygen producing carbon dioxide and water only & release energy

• During combustion the hydrogen and carbon atoms in the fuel react with oxygen ( the carbon and hydrogen are oxidised).

• If the oxygen is unlimited, this reaction produces carbon dioxide and water. (This is called complete combustion).

• If limited oxygen →promises carbon monoxide or carbon (soot) →less energy is released and dangerous gases are made

How can hydrocarbons be used as fuels?

-release energy when they burn during combustion (chemical reaction)

+;

• burn easily in air

• Release large amounts of energy per gram

• Readily available from crude oil & natural gas

• Transported & stored easily

Eg:

• natural gas →methane (CH4)→ home heating ,cooking gas

• Petrol → mixture of alkenes → car engines

• Diesel → longer chain alkanes → Lorrie’s & trains

• Kerosene→ medium -chain alkanes → jet engines

Why do we separate hydrocarbons?

Different hydrocarbons have different uses and in order for them to be useful they need to be separated.

(we separate them via fractional distillation)

Writing balanced equations for complete combustion of hydrocarbons?

General formula:

• Hydrogen + O2 → CO2 + H2O

EG: methane:

CH4 + 2O2 → CO2 + 2H2O

Hydrocarbon reacts with oxygen to form carbon dioxide & water

Balanced ;

1 carbon atoms

4 hydrogen

4 oxygen atoms on both sides

Describe fractional distillation

- used to make hydrocarbons in crude oil useful

• Crude oil is separated into fractions →fractions contain hydrocarbons with a similar number of atoms

• Firstly crude oil is heated to a very high temperature →boils →so all of the hydrocarbons evaporate and turn into gas

• The crude oil vapour is now fed into the fractional distillation column. The column is hotter at the bottom and cooler at the top.

• The hydrocarbon vapours now rise up the column. Hydrocarbons condense (turn back into liquid)when they reach their boiling point and the liquid hydrocarbons then collect in trays and drain out.

• Remaining hydrocarbons continue moving up the column & condense when reach their boiling points

• As very long chained hydrocarbons have high boiling points →they’re removed at the bottom of the column

• very short chained hydrocarbons have low boiling points →don’t condense → they’re removed at the top of the column as gases

What are fractions ?

• Some fractions are used as fuels

• Some used as feedstock for petrochemical industry

• Feedstock = a chemical used to make other chemicals

• EG:

  • solvents

  • Lubricants

  • Detergents

  • Polymers(

Why don’t long chained hydrocarbons make very good fuels?

Because they aren’t very flammable

What is cracking?

A chemical process that breaks down long chained hydrocarbons into shorter , more useful hydrocarbons.

What are the products of cracking?

A long chained alkane is converted into a shorter chain alkane and an alkene.

What is catalytic cracking?

Cracking is a type of thermal decomposition which requires high temperature (550 degrees C) and the use of a a catalyst → e.g zeolite

• Heat long chained hydrocarbons to vaporise them

• Then the vapour can be passed over a hot powdered aluminium oxide catalyst

• Converts alkanes → shorter alkanes + alkenes

• Helps meet demeans for petrol & plastics

• Happens faster & at lower temp due to catalyst

What is steam cracking?

Cracking is a type of thermal decomposition which requires high temperature (over 850 degrees C) and steam.

• Heat long chained hydrocarbons→alkane → to vaporise them

• Mix this vapour with steam and the heat them to a very high temperature

• Long chains break apart into :

  • short chain alkanes (used as fuels)

  • Alkenes (to make plastic)

What is an Alkene and its formula ?

• type of hydrocarbon that contains at least one carbon-carbon double bond (C=C)

• Unsaturated molecule

General formula :

CnH2n

• have fewer hydrogen atoms than alkanes

• Are unsaturated hydrocarbons due to → double bonds

Examples of alkenes

• ethene → C2H4

• Propene → C3H6

• Butene →C4J8

Test for alkenes

• add bromine to water to the solutions

Alkene present:

Bromine water turns colourless

Alkene not present:

Bromine water stays orange

Balance an equation for cracking

1)choose shorter alkane

2)work out what’s missing to make the atoms balanced

3)remainder is usually an Alkene (with a C=C double bond and fewer Hs)

EG:

C25H52 → C20H42 + C5H10