Crude oil, hydrocarbons and alkanes .1

what is the only compound that contains hydrogen and carbon atoms only

Hydrocarbons

what is a crude oil and where is it found

• Crude oil is a finite resource

• that is found in the Earth’s crust. (It is the remains of organisms that lived and died millions of years ago - mainly plankton which was buried in mud)

what is crude oil

Crude oil is a complex mixture of hydrocarbons.

how are the carbon atoms joined in hydrocarbons

The carbon atoms in these molecules are joined together in chains and rings

what is crude oil is an important source of (2)

• fuels such as petrol, diesel, kerosene, heavy fuel oil and liquefied petroleum gases

• feedstock for the petrochemical industry

what is a feedstock

A feedstock is a raw material used to provide reactants for an industrial reaction.

what is a petrochemical and give and example

• substance made from crude oil using chemical reactions.

• eg. ethene produced from crude oil.

• used as feedstock to make poly(ethene), a polymer

what are some Other useful substances made from compounds found in crude oil

• solvents

• lubricants

• detergents

what do alkanes form

a homologous series

Like all homologous series, what do the alkanes have the same (4)

• have the same general formula

• differ by CH₂ in molecular formulae from neighbouring compounds

• show a gradual variation in physical properties, such as their boiling points

• have similar chemical properties

what is the general formula for the alkanes

C_nH_2n+2,

what is n in the general formula for alkanes

n is the number of carbon atoms in the molecule.

what are examples of 4 alkanes

• methane

• ethane

• propane

• butane

what is the molecular formula and structural formula of methane

CH4

what is the molecular formula and structural formula of ethane

C2H6

what is the molecular formula and structural formula of propane

C3H8

what is the molecular formula and structural formula of butane

C4H10

what are the alkanes

The alkanes are saturated hydrocarbons:

why are the alkanes hydrocarbons

because they are compounds containing hydrogen and carbon only

why are the alkanes saturated

because their carbon atoms are joined by C-C single bonds

what is Fractional distillation used for

to separate crude oil into simpler, more useful mixtures

why can the Fractional distillation method be used

because different hydrocarbons have different boiling points

what happens during the fractional distillation of crude oil (4) - bbc bitesize one

• heated crude oil enters a tall fractionating column, which is hot at the bottom and gets cooler towards the top

• vapours from the oil rise through the column

• vapours condense when they become cool enough

• liquids are led out of the column at different heights

process of fractional distillation

1. oil is heated until most of it has turned into gas - gases enter a fractionating column (and liquid bit is drained off)

2. in column theres a temp gradient (hot at bottom, cool at top)

3. longer hydrocarbons have high boiling points. they condense back into liquids and drain out the column early on, when they are near the bottom. shorter hydrocarbons have lower boiling point so condense much later on, near to the top of the column where its cooler

4. you end up with the crude oil mixture seperated out into different fractions. each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms so have similar boiling points

what is the structure (how are they held together/built) of Small hydrocarbon molecules and how does this affect them during the fractional distillation of crude oil

• have weak intermolecular forces

• so they have low boiling points

• They do not condense, but leave the column as gases

what is the structure (how are they held together/built) of Long hydrocarbon molecules and how does this affect them during the fractional distillation of crude oil

• have stronger intermolecular forces

• so they have high boiling points

• They leave the column as hot liquid bitumen

what are fractions and why are they called this

• The different, useful mixtures are called fractions

• This is because they are only part of the original crude oil

at the bottom of the fractionating tower what molecules are found and what are the properties of the molecules found here

• hottest part

• large molecules found here

• high boiling point

• not very volatile

• does not flow easily

• does not ignite easily

at the top of the fractionating tower what molecules are found and what are the properties of the molecules found here

• coolest part

• small molecules found here

• low boiling point

• very volatile

• flows easily

• ignites easily

what is the temperature of the fractionating tower at the top

• coolest part

• 25 degrees

what is the temperature of the fractionating tower at the bottom

• hottest part

• 350 degrees

how many parts is the fractionating tower spilt in

4

what are the crude oil fractions and their uses from top to bottom of the fractionating tower

• liquefied petroleum gas

• petrol

• kerosene

• diesel

• heavy fuel oil

• bitumen

what is liquefied petroleum gas use

fuel for domestic heating + cooking

what is petrol use

fuel for cars

what is kerosene use

fuel for aircrafts

what is diesel use

fuel for some cars + trains

what is heavy fuel oil use

fuel for ships + power stations

what is bitumen use

bitumen for roads + roofs

what is one way to remember the names of the fractions

• Lazy

• Penguins

• Keep

• Drinking

• Hot

• Beer

what does each crude oil fraction contain

a mixture of hydrocarbons

what are the hydrocarbons in a fraction mostly

alkanes

what do the alkanes in each fraction have similar but not identical (4)

• numbers of hydrogen and carbon atoms in their molecules

• boiling points

• ease of ignition

• viscosity

what do the gases fraction containing hydrocarbons with one to four carbon atoms have (properties 3)

These have:

• boiling points below room temperature

• they are very flammable

• have a low viscosity

what does the hydrocarbons in the bitumen fraction containing hydrocarbons with more than 35 carbon atoms have as its properties in comparison to the previous factor with 1-4 carbon atoms (3)

These have:

• boiling points well above room temperature

• are very difficult to ignite

• have a high viscosity

what can Hydrocarbon fuels can undergo and what does it depend on

• complete combustion or

• incomplete combustion

• depending on the amount of oxygen available

when does complete combustion of a hydrocarbon fuel happen

when there is a good supply of air

what type of reaction happens when carbon and hydrogen atoms in the fuel react with oxygen and what is the product

• an exothermic reaction

• carbon dioxide and water are produced

• the maximum amount of energy is given out

when does complete combustion happen in a bunsen burner

this occurs when the air hole is fully open

what is the general equation for the reaction

hydrocarbon + oxygen → carbon dioxide + water

what is the equation for the complete combustion of propane, used in bottled gas

propane + oxygen → carbon dioxide + water

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

when does Incomplete combustion happens

when the supply of air or oxygen is poor

what is produced during incomplete combustion and what is the overall energy released

• Water is still produced

• but carbon monoxide and carbon are also produced

• Less energy is released than during complete combustion

when does a incomplete combustion occur in a bunsen burner

incomplete combustion occurs when the air hole is closed

what is cracking + what are the unsaturated substances involved

a reaction in which larger saturated hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules, some of which are unsaturated:

• the original starting hydrocarbons are alkanes

• the products of cracking include alkanes and alkenes, members of a different homologous series

what can hexane be cracked to form + state the word equation + equation

hexane can be cracked to form butane and ethene:

hexane → butane + ethene

C₆H₁₄ → C₄H₁₀ + C₂H₄

during cracking how is the formula/equation of each substance/product known

• The starting compound will always fit the rule for an alkane, C_nH_2n+2.

• The first product will also follow this rule.

• The second product will contain all the other C and H atoms.

• The second product is an alkene, so it will follow the rule C_nH_2n.

what is the alkene general formula

C_nH_2n

question : C₁₆H₃₄ is an alkane which can be used as the starting chemical in cracking. One of the products of cracking this compound is an alkane which has 10 carbon atoms in it. Write a balanced symbol equation for this cracking reaction.

• C₁₆H₃₄ will be the first part of the equation

• question says 10 carbon atoms and we know the first product in a chemical cracking is a alkane and the formula for that is CnH2n+n so it would be C10H22

• then the second part of the product is a alkene and its whats left over so for carbon you would do 16-10=6 and for the hydrogen 34-22=12

• the final answer would therefore be

  C₁₆H₃₄ → C₁₀H₂₂ + C₆H₁₂

what are one of the 2 methods for cracking

• Catalytic cracking

• Steam cracking

what is cracking

thermal decomposition reaction - breaking down molecules by heating them

what is catalytic cracking

uses a temperature of approximately 550°C and a catalyst known as a zeolite which contains aluminium oxide and silicon oxide

what is steam cracking

uses a higher temperature of over 800°C and no catalyst

process of catalytic cracking. bbc bitesize one

1. The structure of hexane

2. The hexane is passed over a hot catalyst

3. Butane and ethene are produced

process of catalyctic cracking

1. heat the long chain hydrocarbons to vapourise them (turn them into gas)

2. vapour is then passed over a hot powered aluminium oxide catalyst

3. long-chain molecules split apart on the surface of the specks of catalyst

process of steam cracking

1. heat the long chain hydrocarbons to vapourise them (turn them into gas)

2. mix them with steam

3. then heat them at very high temperatures

why is cracking important (2)

1. It helps to match the supply of fractions with the demand for them.

2. It produces alkenes, which are useful as feedstock for the petrochemical industry.

what is the supply (definition)

The supply is how much of a fraction an oil refinery produces.

what is the demand (definition)

The demand is how much of a fraction customers want to buy.

what does fractional distillation of crude oil produce very often

• produces more of the larger hydrocarbons than can be sold

• and less of the smaller hydrocarbons than customers want

wha are smaller hydrocarbons more useful as than larger hydrocarbons

as fuels

what does cracking do to larger hydrocarbons and how is this good

• converts larger hydrocarbons into smaller hydrocarbons

• the supply of fuels is improved

• This helps to match supply with demand

what do Alkanes and alkenes both form a series of

Alkanes and alkenes both form homologous series of hydrocarbons

what is the difference between alkenes and alkanes and what does this result to (2)

• alkanes are saturated, their carbon atoms are only joined by C-C single bonds

• alkenes are unsaturated, they contain at least one C=C double bond

As a result, alkenes are more reactive than alkanes. Alkenes can take part in reactions that alkanes cannot

what will ethene molecules react together to form

poly(ethene), a polymer.

what will happen when alkenes react with bromine water and how is this useful for testing

• turn it from orange/brown to colourless.

• This is the way to test for a double C=C bond in a molecule.