Organic Chemistry Flashcards
What is organic chemistry?
The chemistry of CARBON ATOMS
Carbon forms a vast umber of compounds because it can form strong covalent bonds with itself
What is a functional group?
A specific atom or group of atoms which confer certain physical and chemical properties onto the molecule
What is a homologous series?
Organic compounds with the same functional group but a different number of carbon atoms are said to belong to the same HOMOLOGOUS SERIES.
Each member has the same functional group
Each member has the same general formula
Each member has similar chemical properties
As the homologous series is ascended, the size of the molecule increases, which has an effect on physical properties, such as boiling point and density
What is the general formula of alkenes?
CnH2n
What is the displayed formula?
Shows the spatial arrangement of all the atoms and bonds in a molecule
What is the molecular formula?
Shows the actual number of each atom in a molecule, one molecule at a time
What is crude oil?
A finite resource which we find in the Earth’s crust, which is a mixture of hydrocarbons which also contain natural gas.
It is a thick, sticky, black liquid that is found in porous rick which was formed over millions of years ago from the effects of high pressures and temperatures on the remains of plants and animals
What is an alkane?
A group of saturated hydrocarbons.
General formula is CnH2n+2
Colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases.
Generally uncreative compounds but they undergo combustion reactions and can be cracked into smaller molecules as well as reacting with halogens in the presence of light
What does saturated mean?
Containing the greatest number of hydrogen atoms.
They only have single carbon-carbon bonds and there are no double bonds
Why is crude oil so useful?
Crude oil itself is NOT useful, but the different hydrocarbons that make up the mixture, called fractions are EXTREMELY VALUABLE, with each fraction having many different applications.
Each fraction consists of groups of hydrocarbons of SIMILAR CHAIN LENGTHS.
These fractions in petroleum can be separated in FRACTIONAL DISTILLATION.
The size and length of these fractions determine which fraction they will be separated into.
Most fractions contain MANY ALKENES
What is fractional distillation?
A separation technique used to separate in this example CRUDE OIL in a fractionating column, which is very hot at the bottom and cool at the top
Crude oil enters the fractionating column and is heated so vapour rises
Vapours of hydrocarbons with very high boiling points immediately condense into liquid at the higher temperatures lower down and are tapped off at the bottom of the column
The fractions containing SMALLER hydrocarbons are collected at the TOP of the fractionating column as gases
The fractions containing BIGGER hydrocarbons are collected at the lower sections of the fractionating column
What are petrochemicals?
Chemicals obtained from the process of fractional distillation of petroleum
What can petrochemicals be useful for?
- Useful in most transport lines
- Liquidified petroleum gas (domestic heating and cooking)
- Petrol (Fuel for cars)
- Kerosene (Jet fuel (paraffin))
- Diesel (Diesel engines (gas oil))
- Heavy fuel oil (Ships and power stations)
- Bitumen (Surfacing roads and roofs)
What do the properties of hydrocarbons depend on?
The size of the molecule, (how many carbons there are)
Functional group
What happens to the properties of hydrocarbons as their sizes increase and why?
Boiling point increases due to the molecules getting larger so there are more intermolecular forces of attraction between the molecules so more energy is required to break these forces and separate the molecules
Viscosity also increases with chain length.
As hydrocarbons increase in size, flammability DECREASES.
What is viscosity?
Refers to the FLOW of a liquid
High viscosity liquids are THICK and flow less easily
Low viscosity means the liquid is RUNNY
What is complete combustion?
When WATER and CARBON DIOXIDE are formed at the end of a reaction
What is the equation for the combustion of methane?
CH4 + 2O2 –> CO2 + 2H2O
Why are alkenes unsaturated compounds?
Because they have double C–C bonds, meaning that there is not the maximum amount of hydrogen atoms present
What is cracking?
A process whereby long-chain hydrocarbons are broken down and CRACKED to produce smaller chain hydrocarbons
What are the 2 methods for cracking?
Catalytic cracking and steam cracking
What is catalytic cracking?
Involves heating the hydrocarbon molecules to around 470-550°C to vaporise them
Then the vapours pass over a hot powdered catalyst of aluminium oxide
This process breaks covalent bonds in the molecules as the come into contact with the surface of the catalyst causing THERMAL DECOMPOSITION where the molecules are broken up in random ways to produce mixtures of SMALLER alkanes and alkenes
What is steam cracking?
Involves using slightly higher temperatures than Catalytic cracking, and produces more ring structures and UNSATURATED COMPOUNDS
The vaporised hydrocarbons are mixed with STEAM and heated to a high temperature which induces cracking and forms the smaller alkanes and alkenes
What happens when we write equations for cracking?
The C and H atoms must add to make the same number om both sides, eg.
C6H16 –> C4H10 + C2H4
What are alkenes?
A hydrocarbon compound with ATLEAST ONE double bond between two of the carbon atoms in the chain
The general formula of alkenes is CnH2n
They are MORE REACTIVE than ALKANES due to the presence of the C–C double bond, so they can take part in reactions in which alkanes cannot, so they are more useful and desired than alkanes
They can be used to make polymers and are the starting materials for the production of many other chemicals
What is the bromination of Ethene?
Where ethene undergoes an ADDITION REACTION in which atoms of a simple molecule add across the C–C double bonds
How can we tell apart alkenes and alkanes?
Alkenes can undergo reactions which alkanes CANT, so we can use a simple test called the BROMINE WATER TEST to tell them apart
How does the bromine water test work?
Bromine water is a coloured (orange) solution, so when bromine water is added to two samples of an alkane and an alkene, when added to the alkane there will be no colour change because bromine and the alkane wont react, so the bromine remains in solution.
However when the bromine water is added to the alkene, the bromine atoms add across the C–C double bond, so the solution no longer contains free bromine so it loses its colour
What is the functional group of an alkene?
C–C double bond
What is special about alkenes being unsaturated?
They can make more bonds with other atoms by opening up the C–C bond and allowing incoming atoms to form another single bond with each carbon atom
What happens when alkenes are combusted?
Alkenes can undergo complete and incomplete combustion but because of the higher carbon to hydrogen ratio they tend to undergo incomplete combustion, producing a smoky flame in the air
When does complete combustion occur?
When there is EXCESS OXYGEN
When does incomplete combustion occur?
When there is INSUFFICIENT OXYGEN to burn.
Carbon MONOXIDE and SOOT in the form of carbon can be formed in this case
What is hydrogenation?
When alkenes undergo ADDITION REACTIONS with HYDROGEN in which an ALKANE is formed.
This occurs at 150°C using a NICKEL CATALYST
What is a hydration reaction?
Where water is added to the molecule when an alkene undergoes an addition reaction with steam where an ALCOHOL is formed
What is halogenation?
When a halogen participates in addition reactions with alkenes, eg. Bromine
What is the functional group of an alcohol?
(-OH)
What is the formula of an alcohol?
CnH2n+1OH
How can ethanol be produced?
By fermentation where sugar or starch is dissolved in water and yeast is added. It is fermented between 15 and 35°C WITHOUT Oxygen for a few days, and yeast enzymes break down the sugar into glucose. The yeast is killed off once the concentration of the alcohol reaches 15%
How can ethanol be used?
Alcoholic drinks, fuels, solvents
What does Ethanol look like?
A colourless liquid that dissolves in water to form NETRAL solutions
Why are methanol and ethanol such good solvents?
Because they can dissolve many substances that water CANNOT , such as fats and oils, but can also dissolve most of the substances that water CAN
What happens when alcohols undergo complete combustion?
Forms CARBON DIOXIDE and WATER
How are carboxylic acids formed?
When an alcohol undergoes OXIDATION, carboxylic acids are produced
What is the general formula of a carboxylic acid?
CnH2n+1COOH
What happens as the size of the carboxylic acid increases?
Its viscosity increases (so it becomes thicker) and its boiling point increases, (more intermolecular forces)
What happens when a carboxylic acid reacts with metals?
Forms SALT + Hydrogen
What happens when carboxylic acids react with hydroxides?
Salt and Water are formed in a NEUTRALISATION reaction
What happens when a carboxylic acid reacts with carbonates?
Metal salt, water and CO2 are produced
What happens when carboxylic acids and alcohols react?
ESTERS are formed in ESTERIFICATION
What is the functional group of an ester?
(-COO)
Why are carboxylic acids weak acids?
Because they only PARTLY IONISE when dissolved in water (pH values between 3 and 7)
Ethanoic acids for example is around 95% undissociated
So out of 100 molecules, only about 5 actually ionise
What are polymers?
Polymers are large molecules of high relative molecular mass and are made by linking together large numbers of smaller molecules called MONOMERS
What are monomers?
Monomers are small molecules connected to adjacent repeating units within a polymer via adjacent bonds
What are the different types of polymers?
Synthetic (man made, such as plastics) and biological, (natural ones, such as DNA)
What do polymerisation reactions often require?
HIGH PRESSURES and the use of a CATALYST
How do we represent polymer formula on paper?
We use their REPEATING UNIT
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What is condensation polymerisation?
Where two different monomers are linked together to form a polymer + one water molecule PER LINKAGE
The monomers have TWO FUNCTIONAL GROUPS PRESENT, where they are at EACH END of the monomer.
The functional groups at the ends of one monomer react with the functional group on the end of the other monomer, creating long chains of ALTERNATING MONOMERs and producing WATER
What are amino acids?
Small molecules containing the amino, NH2, and the carboxylic acid functional group
There are 20 naturally occurring amino acids and they all have the same general structure
What are polypeptides?
Polypeptides are condensation polymers which are formed from AMINO ACID monomers joined together by peptide links
What is DNA?
A large molecule which consists of 4 different monomers called nucleotides containing genetic information encoding instructions to which organisms need to develop and function correctly.
Nucleotides form two strands that intertwine causing the famous double helix.
The nucleotides contain smaller molecules called BASES which are abbreviated to A, T, C and G which are bound together by polymerisation
What are simple carbohydrates?
Monosaccharides, such as SUGARS like fructose and glucose
What are complex carbohydrates?
Polysaccharides, such as STARCH and CELLULOSE
the monomers which form these are sugars
What are protein based natural polymers?
Haemoglobin, Antibodies and Enzymes
