organic chemistry Flashcards
Define crude oil
- a finite resource found in rocks.
- the remains of an ancient biomass consisting mainly of plankton that was buried in mud.
What is crude oil a mixture of?
- a mixture of a very large number of compounds.
- chemical properties of each substance in the mixture are unchanged
What is crude oil made up of?
- most of the compounds in crude oil consist of hydrocarbons
- molecules made up of hydrogen and carbon atoms only.
Define homologous series
- A group of organic compounds that react in a similar way
What are the most of the hydrocarbons in crude oil?
- alkanes
What are alkanes?
- saturated hydrocarbons - each carbon atom forms four single covalent bonds
What is the general formula for alkanes?
- CₙH₂ₙ₊₂
What are the first four members of the alkanes?
- methane, ethane, propane and butane
Show how can alkanes be represented
C₂H₆
H H
| |
H—-C—C—-H
| |
H H
How can hydrocarbons in crude oil be separated?
- hydrocarbons in crude oil may be separated into fractions by fractional distillation
- each of which contains molecules with a similar number of carbon atoms
Explain how fractional distillation works
- The oil is heated in the fractionating column and evaporates and condenses at a number of different temperatures.
- In the bottom there is a temp gradient (hot at the bottom, cooler as you go up)
- The longer the hydrocarbons, the higher the b.p so they condense back into liquids and drain out of the column early on.
- Shorter hydrocarbons condense later on
- The fractionating column works continuously
- Heated crude oil is piped in at the bottom.
- The vaporised oil evaporates and rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
- The many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms
What can the fractions be processed to produce?
- can be processed to produce fuels and feedstock for the petrochemical industry
What are the uses of crude oil?
- many fuels that we depend on for our modern lifestyle are produced from crude oil
e.g. petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases
What industry produces useful materials that our modern life depends on?
- the petrochemical industry produces many useful materials that modern life depends on
e.g. solvents, lubricants, polymers, detergents
How does the vast array of natural and synthetic carbon compounds occur?
- due to the ability of carbon atoms to form families of similar compounds
What do the properties of hydrocarbon depend on?
- the size of their molecules, which affects boiling point, viscosity and flammability
- these properties influence how hydrocarbons are used as fuels.
Describe how boiling point changes as the molecular size of hydrocarbons increase
- the shorter the molecules, the lower the temp at which that fraction is vaporised or condensed
- and the lower its boiling point (therefore more volatile)
Describe how viscosity changes as the molecular size of hydrocarbons increase
- the shorter the molecules, the less viscous it is
- the longer the molecules, the more viscous it is
Describe how flammability changes as the molecular size of hydrocarbons increase
- the shorter the molecule, the more flammable it is
Define volatile
- Turns into a gas at a lower temperature
Why are hydrocarbons burnt?
- so that they can be used as fuel since the reaction produces energy
What happens when hydrocarbons are burnt?
- the combustion of hydrocarbon fuels releases energy
- during combustion, the carbon and hydrogen in the fuels are oxidised.
- produces carbon dioxide
and water (complete combustion)
What is the word equation for hydrocarbon, carbon dioxide and water?
hydrocarbon + oxygen –> carbon dioxide + water + energy
How can hydrocarbons produce smaller molecules?
- hydrocarbons can be cracked (broken down) to produce smaller, more useful molecules
What type of reaction is cracking?
- Thermal decomposition (breaking molecules down by heating the,?
What are the two methods of cracking?
- catalytic cracking and steam cracking
What happens during catalytic cracking?
- Heat long-chain to vaporise them
- Vapour passed over a hot powdered aluminium oxide catalyst
- Long-chain molecules split apart on the surface
What happens during steam cracking?
- mixes with steam and heated to a very high temp so that thermal decomposition reactions can occur
What are the products of cracking?
- alkanes and alkenes.
Which is more reactive, alkenes or alkanes?
- alkenes are more reactive than alkanes due to their C=C
- they react with bromine water (used as a test for alkenes)
What happens when bromine water reacts with an alkene?
- react with bromine water, turning it from orange to colourless
Why are the products of cracking useful as fuels?
- because there is a high demand for fuels with small molecules
- products of cracking have shorter chains making them more flammable
What are alkenes used to produce?
- polymers
- as starting materials for the production of many other chemicals.
How to balance cracking equations
- same number of carbons and hydrogens on each side of the equation
- going from a bigger molecule to usually 2 smaller molecules
Why is cracking useful?
- Short-chain hydrocarbons are flammable so make good fuels and are in high demand
- Can also be used to produced alkenes as a starting material when making lots of other compounds and can be used to make polymers
- Useful as fuels
What are alkenes?
*unsaturated hydrocarbons with a double carbon-carbon bond
What is the general formula for alkenes?
- CnH2n
Why are alkene molecules unsaturated?
- because they contain two fewer
hydrogen atoms than the alkane with the same number of carbon
atoms
Why are alkenes more reactive than alkanes?
- The C=C can open up to make a single bond, allowing the two carbon atoms to bond with other atoms
What are the first four members of alkenes?
- ethene, propene, butene and pentene
Show how alkenes can be represented
C₃H₆
H H H
| | |
H—C—C=====C
| |
H H
What is the functional group of alkenes?
- C=C (carbon carbon double bond)
What determines the reactions of organic compounds?
- the generality of reactions of functional groups
Describe what happens when alkenes react with oxygen
- in LARGE amounts of oxygen, alkenes combust completely (like other hydrocarbons)
- However, burn in air = incomplete combustion
- but tend to burn in air with smoky
flames due to incomplete combustion (CO is formed) - Alkene + oxygen -> carbon + carbon monoxide + CO2 + H2O
- Yellow flame and less energy released
Describe what happens when alkenes react with hydrogen, water and the halogens
- react with hydrogen, water and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond
Define functional group
- Group of atoms in a molecule that determines how that molecule typically reactions
Describe alkene reactions via addition reactions
- Most o the time, alkenes react via addition reactions
- Carbon double bond will open up to leave a single bond and a new atom is added to each carbon
R H H X
I I I I
C=C + X-Y –> R-C-C-H
I I I I
H H Y H
Describe the alkenes reaction with hydrogen
- Hydrogen react with C=C to open up the double bond and form the equivalent saturated alkane (reacted in presence of a catalyst)
- a.k.a hydrogenation
Give an example of an alkene reaction with hydrogen
R H H H
I I I I
C=C + H2 –> R-C-C-H
I I I I
H H H H
Describe alkenes reaction with halogens
- React in addition reactions with halogens such as bromine, chlorine and iodine
- Molecules formed are saturated with C=C carbons each becoming bonded to a halogen atom
Give an example of an alkene reaction with halogens
- Bromine + ethene -> dibromoethane
H H H Br
I I I I
C=C + Br2 –> H-C-C-H
I I I I
H H H Br
Describe the reactions and conditions for the addition of hydrogen
describe the reactions and conditions for the addition of
hydrogen, water and halogens to alkenes
* draw fully displayed structural formulae of the first four
members of the alkenes and the products of their addition
reactions with hydrogen, water, chlorine, bromine and iodine.
Describe how steam can react with alkenes to form alcohols
- When alkenes react with steam, water is added across the double bond and an alcohol is formed
- After the reaction takes place, the mixture is passed into a condenser
- Unreacted gas is recycled back into the reactor, alcohol can be purified from mixture by fractional distillation
Give an example of an alkene reaction with steam
H H H H
I I I I
C=C + H2O –> H-C-C-O -H
I I I I
H H H H
What is the functional group of alcohols?
- –OH
What are the first four members of alocohols?
- methanol, ethanol, propanol and butanol
What is the general formula of an alcohol?
CnH2n+1 OH
Show how you can represent alcohols
- CH3CH2OH
H H
| |
H—-C——–C—-O–H
| |
H H
Describe the properties of alcohol
- Flammable - undergo complete combustion in air to produce CO2 and water
*M,E, P. B all soluble in water, solutions have neutral PH - React with sodium
- Can be oxidised by reacting with oxygen to produce a carboxylic acid
Describe what happens when the first four alcohols react with sodium
- produces hydrogen and a salt (H given off and Na added)
Describe what happens when the first four alcohols burn in the air
- produces carbon dioxide and water
Describe what happens when the first four alcohols are added to water
- dissolve in water to form a neutral solution (pH of 7)
Describe what happens when the first four alcohols react with an oxidising agent
- form carboxylic acids
What are the main uses of alcohols?
- methanol: chemical feedstock, in anti-freeze, to make biodiesel
- ethanol: the main alcohol in alcoholic drinks, used as a solvent and fuel
- all 4: can be used as fuels
What happens when sugar solution are fermented using yeast?
- aqueous solutions of ethanol are produced
What are the condition used for fermentation of sugar using yeast?
- about 35°C
- anaerobic (without oxygen)
- yeast enzyme catalyst
Name the word equation for sugar, ethanol and carbon dioxide
Sugar → ethanol + carbon dioxide
What is the functional group of carboxylic acid?
- –COOH
- names end in -anoic acid
What are the first four members of carboxylic acids?
- methanoic acid, ethanoic acid, propanoic acid and butanoic acid
Show how can carboxylic acids be represented
CH3COOH
H
|
H——-C—-C=O
| |
H O-H
Describe what happens when the first four carboxylic react with metal carbonates
- produces carbon dioxide (turns limewater
cloudy), a salt and water - salts formed in these reactions end in -anoate
e.g. methanoate - ethanoic acid + sodium carbonate –> sodium ethanoate + water + carbon dioxide
Describe what happens when the first four carboxylic dissolve in water
- ionise and realeases H+ ions resulting in acidic solutions
- Do not ionise completely, so form weak acidic solutions (have a higher pH than aqueous solutions of strong acids with eh same conc)
- produces acidic solutions (pH 7)
Describe what happens when the first four carboxylic react with alcohols in the presence of an acid catalyst
- produces esters
- e.g. ethyl ethanoate
- ethanoic acid + Ethanol –> ethyl ethanote + water
What are the function group of esters?
- -COO-
Explain why carboxylic acids are weak acids in terms of ionisation and PH
- they do not ionise completely in solutions so do not release many H+ ions making carboxylic acids weak acids.
- this means they have a higher pH (less acidic) than solutions of strong acids of
the same concentration.
What can alkenes be used to make?
- polymers such as poly(ethene)
- poly(propene) by addition polymerisation.
Define polymer
- Long molecules formed when lots of small molecules called monomers join together
What is a polymer reaction called?
- Polymerisation - usually needs high pressure and a catalyst
What happens in addition polymerisation reactions?
- many small molecules (monomers) join together to form very large molecules (polymers).
What are addition polymers made from and describe this
- Made from unsaturated monomers
- Monomers 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
- When 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 if formed
Show how addition polymerisation can be represented
H H H H
| | | |
n (C=C ) —->- ( —C—C— ) -
| | | |
H H H H n
Why does the repeating unit in addition polymers have the same atoms as the monomer?
- because no other molecule is formed in the reaction.
What happens during condensation polymerisation?
- involves monomers with two
functional groups. - when these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions.
Describe condensation poylmerisation
- Monomers react together and bonds form between them making polymer chains
- For each new bond that forms, a small molecule is lost (hence condensation_
What are the simplest polymers produce from?
- two different monomers with two of the same functional groups on each monomer.
Example of a polymer and condensation polymerisation
- ethanediol
HO—CH2—CH2—OH or HO—- —– OH
How many functional groups do amino acids have?
- two different functional groups in a molecule.
- NH 2 group and also the carboxylic acid group -COOH.
What happens when amino acids react by condensation polymerisation
- produce polypeptides
- Amino group of amino acid can react with the acid group of another to form a polymer chain - for every new bond that is formed a molecule of water is lost
Example of amino acids reacting by condensation polymerisation
For example: glycine is H2NCH2COOH and polymerises to produce
the polypeptide
-(-HNCH2CO)- n and n H2O
Describe the difference between addition and condensation polymerisation
ADDITION
* only one monomer type containing a C=C bond
* only one product formed
* C=C double bond in monomer (functional group involved in polymerisation)
CONDENSATION
* two monomer types each containing two of the same functional groups OR one monomer type with two different functional groups
* Two types of product, polymer and small molecule
* Two reactive groups on each monomer (functional group involved in polymerisation)
What can different amino acids be combined into?
- can be combined in the same chain to
produce proteins. (long chains of polypeptides)
What are the uses of protein in the human body?
- Majority of body tissue made from proteins
- Antibodies
- Enzymes
What does the order of amino acids determine?
- Order gives proteins their different properties and shapes
What does DNA do?
- DNA (deoxyribonucleic acid) is a large molecule essential for life.
- encodes genetic instructions for the development and functioning of living organisms and viruses
What are DNA molecules made up of?
- most DNA molecules are two polymer chains of monomers
- made from four different monomers called nucleotides, in the form of a double helix.
- Each nucleotide contains a base, A C T G
- The bases pair up and form cross links, keeping the two strands of nucleotides together giving a double helix structure
- Order of bases acts as a code for an organism’s genes
What are the other naturally occuring polymers important for life?
- proteins, starch and cellulose
Define sugars
- Small molecules that contain carbon, oxygen and hydrogen
What happens when sugars react together through polymerisation?
- Form larger polymers
What are the types of monomers which these naturally occurring polymers are made?
- proteins - amino acid
- starch - glucose
- cellulose - glucose
