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Topic 7 Organic Chemistry By Bethan Poole (7.1 Carbon Compounds as fuels…
Topic 7 Organic Chemistry
By Bethan Poole
7.1 Carbon Compounds as fuels and feedstock
:fuelpump:
7.1.1 Crude oil, hydrocarbons and alkanes
Crude oil
Formed over millions of years from fossilised remains of plankton
Found in porous rocks in the Earth's crust
A finite resource- used to produce fuels and other chemicals
Mixture of very large compounds- most are hydrocarbons
Alkanes
Carbon atoms are linked to four other atoms by single bonds
Methane
Only contain a single bond- described as
saturated
hydrocarbons
Fairly unreactive but they burn well
General formula:
Can be drawn with a single line between atoms (represents a single covalent bond)
Shorter-chain alkanes release energy more quickly by burning, so there is greater demand for them as fuels
Ethane
Propane
Chemicals that form a homologous series and only have single bonds
7.1.2 Fractional Distillation and petrochemicals
Fractional distillation
Crude oil can be separated into different fractions
Each fraction contains hydrocarbon molecules with a similar number of carbon atoms
Most hydrocarbons obtained are alkanes
1)
Crude oil heated until it evaporates
2)
Vapour moves up the fractionating column
3)
Top of column much cooler than bottom
4)
Shorter hydrocarbon molecules can reach top before condensing and are collected
5)
Longer hydrocarbon molecules condense at higher temps.- collected lower down the collumn
Petrochemicals
Fractional distillation can be used to produce fuel and feedstock for petrochemical industries
Alkanes can be used to make
Motor oils
Solvents
Plastics
7.1.3 Properties of hydrocarbons
Hydrocarbons
Made of hydrogen and carbon
Molecules vary in size- affects properties and uses as fuels
Larger hydrocarbon-
More viscous
Higher boiling point
Less volatile
Less easily it ignites
Combustion
During combustion of hydrocarbons
Both carbon and hydrogen oxidised
Energy released
Waste products produced- released into atmosphere
When burnt with oxygen
hydrogen + oxygen -> water vapour
2H2 + O2 -> 2H2O
Most fuels compounds of carbon and hydrogen- many also contain sulfur
7.1.4 Cracking and alkenes
Cracking
During Cracking
Hydrocarbons heated until they vapourise
Vapour passed over a hot catalyst
Thermal decomposition reaction then takes place
Products include alkanes and alkenes
Example
Long-chain alkane -> short-chain alkane + alkene
Decane -> octane + ethene
C10H22 -> C8H18 + C2H4
Longer chain hydrocarbons can be broken down into shorter, more useful hydrocarbons (Cracking)
Some products useful as fuels- high demand for fuels with small chains of carbon atoms- easy to ignite and have low boiling points
Alkenes can be used to make a range of new compounds, including polymers and industrial alcohol
Alkenes
Bromine water
Alkenes more reactive than alkanes
React when shaken with bromine water- turns orange to colourless- used to differentiate between alkanes and alkenes
ethene (colourless) + bromine water (orange brown) -> colourless solution
ethane (colourless) + bromine water (orange brown) -> Orange brown solution
Ethene reacts with bromine to form dibromoethane in an addition reaction-
C2H4+ Br2 -> CH2BrCH2Br
7.3 Synthetic an naturally occurring polymers
:leaves:
7.3.1 Addition polymerisation
Alkenes are unsaturated- useful for making other molecules especially polymers (long-chain molecules)
Many monomers (small molecules with double bonds) can join to make polymers (addition polymerisation)
Plastics are all synthetic polymers made this way
Can be represented like this-
General formula
In reactions
Repeating unit and the monomer units contain the same atoms
Percentage atom economy is 100%
7.3.2 Condensation polymerisation
Involves monomers with two functional groups
When they react small molecules like water tend to be lost
Simplest polymers formed when diols and dicarboxylic join
General formula
Amino acids join to form polypeptides and water
7.3.3 Amino Acids
Contain two functional groups
Amine group (NH2)
Carboxyl group COOH
Example
Glycine is an amino acid
NH2CH2COOH
Different amino acids join to form proteins
React by condensation polymerisation to form peptides
7.3.4 DNA and other naturally occurring polymers
Large molecule essential for life
Encodes genetic instructions for the development and functioning of living organisms
In the shape of a double helix
Made from two polymer chains- constructed from 4 nucleotides
Starch and Cellulose
Polymers of sugar
Made by plants and are important for life
All a carbohydrates
7.2 Reactions of alkenes and alcohols
:wine_glass:
7.2.1 Structure and formulae of alkenes
Carbon atoms can form double bonds
So...
Carbon atoms don't have to be joined to four other atoms
A carbon-carbon (C=C) bond can be present instead
Hydrocarbons that have double bonds are described as
unsaturated
General formula
Propene (C3H6)
Butene (C4H8)
Ethene (C2H4)
7.2.2. Reactions of alkenes
More reactive than alkanes due to C=C bonds
React withoxygen in combustion reactions
Tend to burn with smokier flames due to incomplete combustion
Hydrogen can be added to alkenes to produce alkanes- nickel catalyst used- done at 150C-
propene+ hydrogen-> propane
C3H6+H2-> C3H8
(addition reaction)
Ethanol can be produced by reacting ethene with steam in the presence of phosphoric acid (catalyst)-
ethene+steam->ethanol
C2H4+H2O -> C2H5OH
(addition reaction)
React with hydrogen, water and halogens- by addition of atoms across the carbon-carbon double bond so the double bond becomes a single bond
Reaction with water (steam at high temp. and pressure)
Propene + Water -> Propanol
With halogens at room temp.
Propene + Chlorine -> Dichloroethane
7.2.3 Alcohols
Fermentation
Aqueous solutions of ethanol can be produced by the fermentation of sugar (renewable source)
Sugar -> ethanol + carbon dioxide
Temperature
Temps. of 25C-50C work best
Too low- Yeast becomes inactive and rate of reaction slows
Too high- Yeast denatured and stops working
Alcohols
Carbon-based molecules- contain functional group hydroxyl
-OH
Methanol, ethanol, propanol, butanol- 1st four member of the homologous series of alcohols
Methanol (CH3OH)
Ethanol (CH3CH2OH)
Properties
dissolve in water to form neutral solutions
react with sodium to produce hydrogen
burn in air to produce carbon dioxide and water
used as fuels and solvents
Alcoholic drinks contain ethanol
Ethanol can be oxidised to ethanoic acid by chemical oxidising agents or by the action of bacteria in air
Ethanoic acid- main acid in vinegar
7.2.4 Carboxylic acids
Carboxylic acids
Organic compounds that contain the functional group carboxyl,
-COOH
Properties
Dissolve in water to form acidic solutions
React with carbonates to produce carbon dioxide
React with alcohols to form esthers
Do not ionise fully in water- called weak acids
Methanoic acid (HCOOH)
Ethanoic acid (CH3COOH)
Propanoic acid (C2H5COOOH)
Esthers
Alcohols and carboxylic acids react together to form esthers
Contain the functional group
-COO
When ethanol and ethanoic acid react they form the ethyl ethanole
Ethanoic acid + Ethanol -> ethyl ethanoate + water
Catalyst needed for the reaction to take place
Properties
Volatile compounds
Distinct smells and are used in perfumes and food
Ethyl Ethanoate (CH3COOC2H5)
