organic chemistry

what is a hydrocarbon

a compound made of hydrogen and carbon atoms only

what is an alkane

A saturated (single bonds only) hydrocarbon

what is an alkene

An unsaturated (double bonds) hydrocarbon

The shorter the carbon chain the …

the more runny a hydrocarbon is (less viscous) - If the number of carbon atoms increases, the attraction between the hydrocarbon molecules also increases which results in the liquid becoming more viscous with the increasing length of the hydrocarbon chain

• The liquid flows less easily with increasing molecular mass

shorter hydrocarbons (at top of tower) are

more volatile (lower boiling points) + more flammable bcs 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

properties of hydrocarbons affect

how they are used for fuels

what is complete combustion

it happens in the presence of oxygen + produces the waste products of carbon dioxide and water vapour

during combustion …

Both carbon and hydrogen from the hydrocarbon are oxidised

why are hydrocarbons used as fuels

due to the amount of energy released when they combust completely

what is crude oil

a fossil fuel formed by the remains of plankton that died and were buried in mud

what is crude oil made up of

A mixture of different hydrocarbons

how are compounds in crude oil separated in fractional distillation

1. oil is heated until most of it has turned into gas and enters the fractioning column

2. there's a temperature gradient in the column

3. longer hydrocarbons have high boiling point so condense back into liquids and drain out of the column early on however the shorter hydrocarbons have lower boiling points so rise to the top of column and then condense

4. this leaves crude oil separated into different fractions

5. these fractions all have a mixture of hydrocarbons which have a similar amount of carbon atoms = similar boiling points

What are the fractions of crude oil? (top to bottom) + a use for each

refinery gases - bottled gas,gasoline - fuel for cars,kerosene - aircraft fuel,diesel - fuel for cars/lorries/buses, fuel oil - fuel for ships/power stations, bitumen - roads/rooftops

what is cracking

Splitting up long chain hydrocarbons

why do we use cracking

short chain hydrocarbons are flammable = good fuels = high demand

what is also produced in cracking

alkenes

what can alkenes make

other compounds and polymers

what type of reaction is cracking

thermal decomposition + endothermic

what is thermal decomposition

breaking down molecules by heating them

what happens in catalyctic cracking + conditions needed for it

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

2. The vapours then pass over a hot powdered catalyst of aluminium oxide (alumina)

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

what happens in steam cracking

1. Long-chain hydrocarbons are vaporized. 

2. The vaporized hydrocarbons are mixed with steam. 

3. The mixture is heated to very high temperatures (over 850°C) and maintained under pressure. 

4. This high temperature and pressure cause the long hydrocarbon chains to break down into smaller molecules, primarily alkanes and alkenes. 

5. The products are then separated by fractional distillation. 

what does a carbon carbon double bond mean

that alkenes have two fewer hydrogens compared with alkanes containing the same number of carbon atoms = unsaturated

straight-chain alkenes have..

twice as many hydrogen atoms as carbon

if there isn't enough oxygen in the air …

incomplete combustion occurs

why is carbon monoxide dangerous

it is a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death bcs the CO binds to haemoglobin so cannot bind to oxygen

fuels are burned in engines = high temperatures = what reacts and what does it produce?

nitrogen and oxygen from the air react to produce nitrogen oxides

• 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

• Exhaust gases also contain unburned hydrocarbons and carbon monoxide

• Cars are fitted with catalytic converters which form a part of their exhaust systems

• Their function is to render these exhaust gases harmless

• The adverse effects of nitrogen oxides include acid rain as well as producing photochemical smog and breathing difficulties, in particular for people suffering from asthma.

after nitrogen oxides have been produced, what can they combine with to produce

combine with water to produce nitric acid

what is the alkene functional group

-C=C-

what is the alcohol functional group

-O-H

what is the carboxylic acids functional group

-C=O-OH

what is the esters functional group

-C=O-O-

what are isomers

compounds with the same molecular formula but different structural formulas

how is acid rain caused

when gases such as sulphur dioxide and nitrogen dioxide dissolve in water in the atmosphere

sulphur dioxide = dissolves into rainwater droplets

nitrogen dioxide = this gas reacts with rainwater and more oxygen to form nitric acid & then when the clouds rise, the temps decrease and the droplets get larger so the droplets containing these acids are heavy enough and fall as acid rain

what can also trigger the formation of nitrogen monoxide & dioxides in air

lightning strikes

How is sulphur dioxide produced from burning fuels.

it comes from sulfur impurities in the hydrocarbon fuels

• Fossil fuels are often contaminated with small amounts of sulfur impurities

• When these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide

 S (s) + O₂ (g) → SO₂ (g)

• 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

halogens react with alkanes to produce + type of reaction

haloalkanes - this is a substitution reaction

chlorine and bromine react with alkanes in the presence of

ultra violet light

Example of UV light + what exactly happens in the substitution reaction between alkanes & bromine

E.g sunlight, a hydrogen atom in the alkane is replaced by a bromine atom

what type of reaction is chlorine and bromine with alkanes and what happens

a hydrogen atom from the alkane is substituted with chlorine or bromine = substitution reaction

What is the alkane general formula?

CnH2n+2

what is the alkene general formula?

CnH2n

Describe the reactions of Alkenes with bromine to produce dibromoalkanes

• alkenes react with bromine water (UV light is not required)

• The double bond is broke and the bromine atoms are added - this is an addition reaction

• During this reaction there is a colour change from orange to colourless

• This is how we can test for the presence of an alkene or another type of unsaturated molecule

How to remember the colour change for alkenes in bromine water?

alkEne - colourlEss - brominE water

3 ways ethanol can be oxidised

• burning in air or oxygen (complete combustion)

• Reaction with oxygen in the air to form ethanoic acid (microbial oxidation)

• Heating with potassium dichromate (VI) in dilute sulfuric acid to form ethanoic acid

2 ways ethanol can be oxidised

• reacting Etheve with steam in the presence of phosphoric acid catalyst at a temp of about 300 degrees and a pressure of about 60-70 atm

• The fermentation of glucose, in the absence of air, at an optimum temp of about 30degrees C and using the enzymes in yeast

Why does fermentation happen in the absence of air At optimum temp

• Fermentation is carried out at temps of 30-40 degrees C because otherwise the enzymes would permanently denature and lose their structure, at temps lower than 30 degrees the process would be too slow

• happens in absence of air bcs the yeast needs to respire anaerobically to produce ethanol (in air the yeast ferments aerobically and produces CO2 and H20 and the ethanol can oxidise to ethanoic acid)

2 pos and negs of hydration of ethene to produce ethanol

Pos

• fast and continuous process

• Produces pure ethanol

Cons

• uses non-renewable crude oil

• High energy costs

2 pos and negs of using fermentation to produce ethanol

Pos

• uses renewable resources

• Low energy process

Cons

• slow and batch process

• Produce impure ethanol

What is vinegar

An aqueous solution containing ethanoic acid

Describe the reactions of aqueous solutions of carboxylic acids with metals and metal carbonates

• metals = dilute carboxylic acids react with metals the same way as other dilute acids e.g hydrochloric but more slowly e.g dilute ethanoic acid reacts with magnesium with a lot of fizzing to produce a salt and hydrogen, leaving a colourless solution of magnesium Ethanoate

• Metal carbonates = dilute carboxylic acids react with metals the same carbonates as they do with other acids, to give a salt, carbon dioxide and water e.g dilute ethanoic acid reacts with sodium carbonate with a lot of fizzing to produce a salt, carbon dioxide and water, leaving a colourless solution of sodium ethanoate

What is ethyl ethanoate + type of reaction

The ester produced when ethanol and ethanoic acid react in the presence of an acid catalyst

this is a condensation reaction because water ( and ethyl ethanoate) is made when two molecules join together

How to find structure/name of an ester

To work out the structure of the ester formed when an alcohol reacts with a carboxylic acid, it is easiest to first draw the structures of alcohol and acid and then remove the H₂O to see what is left when the molecules join.

This is still called propyl ethanoate: the alcohol bit of the name (propyl) comes first and then the carboxylic acid bit (ethanoate), even though the displayed formula is typically written the other way around. Notice that the structural formulae for esters is also typically written with the carboxylic acid bit first, so propyl ethanoate is CH₃COOCH₂CH₂CH₃.

what is a polymer

lots of the same molecules of monomers joined together in one long chain

what does polymerisation require

High pressure and a catalyst

the monomers that make up addition polymers have

a double covalent bond

addition polymerisation is

when unsaturated monomer molecules open up their double bonds to join together to form addition polymer chains.

an addition polymer contains exactly…

the same type and number of atoms as as monomers that formed it

general formula for alcohol

CnH2n+OH

alcohols are flammable and undergo complete combustion in air to form

carbon dioxide + water

alcohols can be oxidised to produce

a carboxylic acid

dif alcohols form

dif carboxylic acids e.g methanol = methanoic acid

why are methanol and ethanol used as solvents

they can dissolve same things as water but also ones water can't

how is ethanol produced

by fermentation which uses an enzyme in yeast to convert sugars to alcohol

what do carboxylic acids react with to produce

react with carbonates to produce salt, water and carbon dioxide

what happens when carboxylic acids dissolve

They ionise and release H+ ions, resulting in an acidic solution.

what is a condensation polymer

A polymer formed when monomers join together and eliminate a small molecule such as water (or hydrogen chloride)

Problems with disposal of addition polymers

• they are inert and cannot biodegrade

• They produce toxic gases when they are burned

what does an amino acid contain

a basic amino group and an acidic carboxyl group

amino acids can form .. via condensation polymerisation

polymers known as polypeptides

sugars can react together through polymerisation to form

larger carbohydrate polymers e.g starch

a carboxylic acid and an alcohol react to form

ester + water

What is produced in condensation polymerisation

Dicarboxylic acid + diol —> polyester + water

Structural display of poly(chloroethene)

Structural display of poly(propène)

Structural display of poly(tetrafluoroethene)

what catalyst is used in esterification

an acid catalyst

esters are :

sweet smelling and volatile

ester functional group

C=O C-O same carbon

naming an ester

(length of carbon chain in alcohol)-yl (length of carbon chain in carboxylic acid)-oate

what is a homologous series

• This is a series or family of organic compounds that have similar 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

Empirical formulae

The empirical formula shows the simplest possible ratio of the atoms in a molecule

Molecular formulae

• The molecular formula shows the actual number of atoms in a molecule

General formula

The general formula shows a ratio of atoms in a family of compounds in terms of 'n' where n is a varying whole number

displayed formula

• The displayed formulae shows the spatial arrangement of all the atoms and bonds in a molecule

structural formula

• 

  In a structural formulae enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted

functional group

• Functional group: A group of atoms bonded in a specific arrangement that influences the properties of the homologous series e.g alkene, alkane, alcohol

naming compounds

• When there is more than one carbon atom where a functional group can be located it is important to distinguish exactly which carbon the functional group is on

• Each carbon is numbered and these numbers are used to describe where the functional group is

• When 2 functional groups are present di- is used as a prefix to the second part of the name

Substitution

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

• Example: Methane reacts with bromine under ultraviolet light

CH₄    +    Br₂       →            CH₃Br   +    HBr

    methane + bromine   →   bromomethane + hydrogen bromide

addition

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

  • Example: Bromine will react with ethene and the bromine molecule will react and add across the double bond of the ethene

C₂H₄     +       Br₂         →         C₂H₄Br₂

ethene   +   bromine   →   dibromoethane

combustion

• This is the scientific term for burning. In a combustion reaction, an organic substance reacts with oxygen to form carbon dioxide (or carbon monoxide if incomplete combustion) and water.

  • Example: Alkenes burn when heated in air of oxygen

• If there is an unlimited supply of air / oxygen, the products are carbon dioxide and water

• This is termed complete combustion

CH₄   +   2O₂   →   CO₂   +   2H₂O

C₃H₈   +   5O₂   →   3CO₂   +   4H₂O

• If there is a limited supply of air / oxygen, the products are carbon monoxide and water

  • This is termed incomplete combustion

CH₄   +   2O₂   →   CO₂   +   2H₂O

C₃H₈   +   5O₂   →   3CO₂   +   4H₂O

colour trend in fractional distillation of crude oil

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

melting/boiling point trend in crude oil distillation

• 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 are the products when a hydrocarbon burns completely in oxygen?

As all hydrocarbons only contain the elements carbon and hydrogen, the only products will be oxides of these elements. So as long as enough oxygen is present for complete combustion, the two products formed will be carbon dioxide (CO₂) and water (H₂O)

What are the possible products of incomplete combustion of hydrocarbons with oxygen in the air?

happens when the supply of air or oxygen is poor. Water is still produced, but carbon monoxide. and carbon (soot) are produced. Less energy is released than during complete combustion.

what happens when te