Organic Chemistry

  • Created by: India.02
  • Created on: 11-06-19 12:42

Hydrocarbon Properties

- The shorter the carbon chain, the more runny the hydrocarbon is - that means it is less viscous (gloopy)

- The shorter thecarbon chain, the more volatile the hydrocarbon is - more volatile means that it turns into a gas at lower temperatures - so the shorter the carbon chain, the lower the temperature at which that hydrocarbon vaporises and condenses - and the lower its boiling point

- The shorter the carbon chain, the more flammable the hydrocarbon

- The properties of hydrocarbons affect how they are used for fuels - short chained hydrocarbons with lower boiling points are used as 'bottled gases' - stored under pressure as liquids in bottles

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Hydrocarbons and Alkanes

- A hydrocarbon is any compund that is formed from carbon and hydrogen atoms only

- Alkanes are the simplest form of hydrocarbon - the general formula is:

- The alkanes are a homologous series - a group of organic compounds that react in a similar way

- They are also saturated compounds - each carbon atom forms four single covalent bonds

- The first four alkanes are methane, ethane, propane and butane

- They can be represented by a displayed formula - a drawing showing all the atoms and bonds in a molecule

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Complete Combustion

- Complete combustion of any hydrocarbon, in oxygen, releases lots of energy - the only waste products are carbon dioxide and water

- During combustion, both carbon and hydrogen are oxidised (oxidation - gain of oxygen)

- Hydrocarbons are used as fuels due to the amount of energy released when they combust completely

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Crude Oil

- It is a fossil fuel thatis formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in the mud

- Over millions of years, with high temperatures and pressure, the remains turn to crude oil, which can be drilled up from the rocks where it is found

- Fossil fuels like coal, oil and gas are called non-renewable fuels as they take so long to make that they are being used up much faster than they are being formed - they are finite resources

- Crude oil is a mixture of lots of different hydrocarbons, most of which are alkanes

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Fractional Distillation

- The different compounds in crude oil are separated by fractional distillation

- The oil is heated until most of it has turned into gas - the gases enter the fractionating column and the liquids are drained off

- In the columnn there is a temperature gradient - it is hot at the bottom and gets cooler as you go up

- The longer hydrocarbons have high boiling points - they condense back into liquids and drain out of the column early on, when they are near the bottom - the shorter ones have a lower boiling point so they ccondense and drain out much later on, near the top of the column where it is cooler

- Crude oil mixture is separated into different fractions - each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points

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Crude Oil Uses

- Oil provides the fuel for most modern transport - heavy fuel oil, diesle oil, kerosene and LPG (liquid petroleum gas) all come from crude oil

- The petrochemical industryuses some hydrocarbons as feedstock to make new compoundsfoe use in things like polymers, solvents, lubricants and detergents

- All products from crude oil are examples of organic compounds (compounds containing carbon atoms)

- The reason that there is such a large variety of products is because carbon atoms can bond together to form different groups called homologous series

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Cracking

- Short-chain hydrocarbons are flammable so they make good fuels and are in high demand - long-chain hydrocarbons form thick liquids that aren't as useful - because of this, longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones by cracking

- Cracking produces alkanes and alkenes - these are used as a starting material when making lots of other compounds can can be used to make polymers - some products of cracking can be as useful as fuels

- Cracking is a thermal decomposition reaction (break molecules down by heating) - heat long-chain hydrocarbons to vaporise them - vapour can be passed over a hot powdered aluminium oxide catalyst - long0chain molecules split apart on the surface of the specks of the catalyst (catalytic cracking)

- You can also crack hydrocarbons if you vaporise them, mix them with steam and heat them to a very high temperature - this is steam cracking

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Alkenes Have A Double Bond

- Alkenes are hydrocarbons that have a double bond between two of the carbon atoms in their chain - the double bond means that alkenes have two fewer hydrogens compared with alkanes containing the same number of carbon atoms - unsaturated

- The double bond can open up to make a single bond, which allows the two carbon atoms to bond with other atoms - this makes alkenes reactive - more reactive than alkanes

- Straight-chain alkenes have twice as many hydrogen atoms as carbon - general formula for alkenes:

- First four alkenes are ethene (with two carbon atoms), propene, butene and pentene

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Incomplete Combustion

- In a large amount of oxygen, alkenes combust completely to produce only carbon dioxide and water - this is complete combustion

- However, when you burn them in air, they tend to undergo incomplete combustion - this is where carbon dioxide and water are still produced by you can also get carbon and carbon monoxide, which is a poisonous gas

- Incomplete combustion results in a smoky yellow flame, and less energy being released compared to complete combustion of the same compound

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Addition Reactions

- A functional group is a group of atoms in a molecule that determines how the molecule typically reacts

- All alkenes have the functional group 'C=C', so they all react in similar ways - you can suggest the products of a reaction based on your knowledge of the alkenes in general

- Most of the time, alkenes react via addition reactions - the carbon-carbon double bond will open up to leave a single bond and a new atom is added to each carbon

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Hydrogen and Halogens

- The addition of hydrogen is known as hydrogenation

- Hydrogen can react with double-bonded carbons to open up the double bond and form the equivalent, saturated alkane

- The alkene is reacted with hydrogen in the presence of a catalyst

- Alkenes will also react in addition reactions with halogens such as bromine, chlorine and iodine - the molecules formed are saturated, with the C=C carbons each becoming bonded to a halogen atom

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Bromine Water and Steam

- The addition of bromine to a double bond can be used to test for alkenes - when orange bromine water is added to a saturated compound, like an alkane, no reaction will occur and the solution will remain bright orange

- If it is added to an alkene, the bromine will add across the double bond, making a colourless dibromo compound - the bromine water is discolourised

- When alkenes react with steam, water is added across the double bond and an alcohol is formed

- The conversion of ethene to ethanol is one way of making wthanol industrially - after the reaction has taken place, the reaction mixture is transferred to a condenser - ethanol and water have a higher boiling point than ethene, so both condense whilst any unreacted ethene gas is recycled back into the reactor - the alcohol is then purified from the mixture by fractional distillation

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Addition Polymers

- Polymers are long molecules formed when lots of small molecules called monomers join together - this is called polymerisation and it usually needs high pressure and a catalyst

- Plastics are made up of polymers - they are usually carbon based and their monomers are often alkenes

- The monomers that make up addition polymers have a double covalent bond

- Lots of unsaturated monomer molecules (alkenes) can open up their double bonds and join together to form polymer chains - this is addition polymerisation

- WHen the monomers react in addition polymerisation reactions, the only product is the polymer, so an addition polymer contains exactly the same type and number of atoms as the monomers that formed it

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Alcohols

- All alcohols contain an -OH group - general formula:

- The first four alcohols are methanol, ethanol, propanol and butanol

- Alcohols are flammable and undergo complete combustion in air to produce carbon dioxide and water

- The first four are all soluble in water - their solutions have a neutral pH

- They also react with sodium - one of the products is hydrogen

- They can be oxidised by reacting them with oxygen to produce a carboxylic acid

- Different alcohols form different carboxylic acids - methanol is oxidised to methanoic acid and ethanol is oxidised to ethanoic acid

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Fermentation and Usage of Alcohols

- Alcohols such as methanol and ethanol are used as solvents in industry - they can dissolve most things that water can dissolve, but they can also dissolve substances that water can't - hydrocarbons, oils and fats

- First four alcohols used as fuels - ethanol used as fuel in spirit burners because it burns fairly cleanly and doesn't smell

- Ethanol is the alcohol found in most alcoholic drinks - made using fermentation

- Fermentation uses an enzyme in yeast to convert sugars into ethanol - carbon dioxide is also produced - the reacton occurs so that the ethanol produced is aqueous:

- Happens fastest at 37 degrees celcius, in a slightly acidic solution and under anaerobic conditions - the enzyme in yeast works best to convert the sugar to alcohol - if conditions were different, the enzyme could be denatured or could work at a slower rate

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Carboxylic Acids

- In a homologous series of compounds that all have '-COOH' as a functional group

- They react like any other acid with carbonates to produce a salt, water and carbon dioxide - the salts formed in these reactions end in 'anoate - methanoic acid will form methanoate

- They can dissolve in water - they ionise and release H+ ions resulting in an acidic solution - they don't ionise completely (not all molecules released the H+ ions) so they only form weak acidic solutions - they have a higher pH than aqueous solutions of strong acids with the same concentration

- Esters have the functional group '-COO-' and are formed from an alcohol and a carboxylic acid - an acid catalyst is also usually used

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Condensation Polymers

- Condensation polymerisation involves monomers which contain different functional groups - the monomers react together and bonds form between them, which makes polymer chains - for each new bond that is formed, a small molecule (water) is lost - this is why it is called condensation polymerisation

- Addition polymerisation - only one monomer type containing a C=C bond - only one product formed - carbon-carbon double bond in monomer is the functional group involved

- Condensation polymerisation - two monomer types each containing the same functional groups or one monomer type with two different functional groups - two types of product are the polymer and the small molecule - two reactive groups on each monomer

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Naturally Occurring Polymers

- An amino acid contains two different functional groups - a basic amino group and an acidic carboxyl group

- An example of an amino acid is glycine - this is the smallest and simplest

- Amino acids can form polymers known as polypeptides via condensation polymerisation - the amino group can react with the acid group, and so on, to form a polymer chain - for every new bond formed, a molecule of water is lost

- One or more long-chains of polypeptides are known as proteins - these have important uses in the human body - enzymes as catalysts - haemoglobin transports oxygen - antibodies form part of the immune system

- DNA is made of two polymer chains of monomers called 'nucleotides' - these each contain a small molecule known as a base - the bases on the different chains pair up with each other and form cross links keeping the two strands of nucleotides together

- Sugars are small molecules that contain oxygen, carbon and hydrogen - sugars can react together through polymerisation reactions to form larger polymers

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