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Organic Chemistry (what I don't know soz will miss stuff out <3)…
Organic Chemistry (what I don't know soz will miss stuff out <3)
Alkenes
Burn with a smoky flame
Alkenes combust completely in enough oxygen - produce water and carbon dioxide
Too little oxygen in the air - don't combust completely - produce carbon (soot) and carbon monoxide (toxic) as well as carbon dioxide and water
Incomplete combustion results in a yellow smoky flame and less energy released compared to complete combustion of the same compound
C
n
H
2n
Are very reactive as they are
unsaturated
Cracking
Thermal decomposition reaction - breaking molecules down by heating them
Catalytic cracking
Heat long-chain hydrocarbons to vaporise them
Pass vapour over hot powdered aluminium catalyst, so long chain molecules split apart on the surface of the powered catalyst
Steam cracking
Vaporise the hydrocarbons, them mix then with steam
Heat them to a very high temperature
Reactions of alkenes
Addition reactions
Alkenes have C=C functional group, so they react in similar ways
C=C bond will open up to leave a single bond, and a new atom is added to each carbon atom
Hydrogenation
The addition of hydrogen
Hydrogen can react with the double-bonded carbons to open up the double bond and form the equivalent, saturated alkane
Done in the presence of a catalyst
Alkenes react with steam to form alcohols
When alcohols react with steam, water is added across the double bond and an alcohol is formed
Eg. ethanol can be made by mixing ethene with steam and then passing it over a catalyst
Conversion of ethene to ethanol is a way to make ethanol industrially
After the reaction, the reaction mixture is passed from the reactor into a condenser - as ethanol and water have a higher point than ethene, they both condense and any unreacted ethene is recycled back into the reactor
Alcohol can then be purified from the mixture by fractional distillation
Halogens react with alkenes
The C=C double bond will open up, and each carbon atom will gain one atom of the halogen, as all the halogens are diatomic
Addition of bromine can be used to test for alkenes
When orange bromine water is added to a saturated compound, like an alkane, no reaction will happen, and it will stay bright orange
If it's added to an alkene the bromide will react with the alkene and the C=C bond will be broken, making a colourless dibromo-compound, so the water is decolourised
Alcohols
General formula of alcohols is
C
n
H
2n+1
OH
Naming system - alkanes but replace -e with -ol
Functional group is OH
Properties of the first 4 alcohols
Flammable (all alcohols) - undergo complete combustion in air when there is enough oxygen
Soluble in water - their solutions have a neutral pH
React with sodium - one of the products is hydrogen
Oxidised by oxygen (oxidising agent) - produce a carboxylic acid (This is why wine tastes acidic when left in open air)
Solvents and fuels
Used as solvents in industry as they can dissolve most things water can dissolve, but can also dissolve other substances, such as hydrocarbons, oils and fats
First 4 alcohols used as fuels eg. ethanol is used in spirit burners - it burns with no smell and is fairly clean
Ethanol - made by fermentation
Uses an enzyme in yeast to convert sugars into ethanol, but also produces carbon dioxide
Reaction occurs in solution so ethanol produced is aqueous
Happens at around 37 degrees, in slightly acidic solution under anaerobic conditions (no oxygen), as this is where yeast works best
Carboxylic acids
Homologous series of compounds with functional group COOH
React like any other acid with carbonates to produce a salt, water and carbon dioxide
The salts formed end in -anoate eg. methanoic acid --> ethanoate
They dissolve in water, and when they dissolve, they release H+ ions, but they don't ionise completely - form weak acidic solutions
React with alcohols
Carboxylic acids react with alcohols to form an ester and water
Esters - functional group -COO-
The reaction is done over an acid catalyst
eg. Ethanoic acid + Propanol --> Propyl Ethanoate + Water
Condensation Polymers
Involves monomers with different functional groups
The monomers react together and bonds form between them, making polymer chains
For each new bond formed, a small new monomer (usually water) is lost
Simplest types of condensation contain two different types of monomer, each with the same functional groups
Polyesters
Formed of monomers of:
A dicarboxylic acid (has 2 COOH functional groups) and a diol (an alcohol with two OH functional groups)
Substances containing both -COOH- and -OH- groups
Addition vs condensation
Monomers
Addition
- only one monomer type containing a C=C bond
Condensation
- Two monomer types each containing two of the same functional group or one monomer type with two functional groups
Products
Addition
- only one product formed
Condensation
- two types of product - monomer and a small product eg. water
Functional groups
Addition
- C=C double bond in monomer
Condensation
- two reactive groups on each monomer
Naturally occuring polymers
Amino acids
Contain amino group (NH2) and a carboxyl group (COOH)
Smallest and simplest amino acid is glycine - CH2 NH2 COOH
Proteins
Polymers on amino acids - polypeptides formed through condensation polymerisation
One or more long chains of polypeptides = protein - lots of uses in body eg. enzymes are catalysts, haemoglobin transports oxygen, antibodies form part of the immune system, and lots of body tissue made from proteins
Order of amino acids is what gives proteins their different properties and shapes
DNA
Made from nucleotide polymers
Contains genetic instructions that allow organisms to develop and operate - double helix structure
Two polymer chains of nucleotides - each contain a base (A, C, G or T), a sugar molecule and a phosphate molecule
Bases on the different polymer chains line up and pair together, forming cross links (hydrogen covalent bonds) keeping the two strands of nucleotides together and giving them a double helix structure (A with T, C with G)
The order of the bases acts as a code for an organism's genes
Simple sugars
Simple sugars that contain oxygen, hydrogen and carbon
Can form polymers
Sugars can react through polymerisation to form larger carbohydrate polymers eg. starch - living things use to store energy, and cellulose - what cell walls are made of (in plants)
Alkanes
C
n
H
2n+2
Less reactive than alkenes as they are
saturated