Organic Chem Flashcards
What is a hydrocarbon
Any compound formed from only hydrogen and carbon atoms
What type of bonds do alkanes have
C-C single bond
What is the formula for alkanes
Cn H2n+2
What is a homologous series
A group of organic compounds that react in a similar way
What are saturated hydrocarbons
When each carbon atom form 4 single covalent bonds
(Alkanes)
List the order of alkanes from 1 carbon atom to 10 carbon atoms
Methane C1 H4
Ethane C2 H6
Propane C3 H8
Butane C4 H10
Pentane C5 H12
Hexane C6 H14
Heptane C7 H16
Octane C8 H18
Nonane C9 H20
Decane C10 H22
Properties of shorter chained hydrocarbons
(Less carbon atoms)
- less viscous (less dense)
- more volatile (can evaporate at lower temperatures)
- so low boiling points
- more flammable
Properties of long chained hydrocarbons
( more carbon atoms)
- viscous (denser)
- not very flammable
- not very volatile (needs higher temperatures to evaporate)
- so high boiling points
Describe the complete combustion of a hydrocarbon
Hydrocarbon + oxygen —> carbon dioxide + water (+ energy)
- both carbon and hydrogen from the hydrocarbon are oxidised
(Gains oxygen, loses electrons) - hydrocarbons are used as fuels due to the amount of energy the release when combusted fully
Balanced equation for the complete combustion of methane
1) CH4 + O2 —> CO2 + H2O
2) CH4 + O2 —> CO2 + 2H2O
3) CH4 + 2O2 —> CO2 + 2H2O
What is crude oil
A fossil fuel formed from the remains of plants and animals, mainly plankton that died millions of years ago and were buried in mud
- over millions of years, with high pressure and temperatures, the remains turned into crude oil
- it can then be drilled up from certain rocks
- a non renewable source (take so long to make, they’re being used up much faster)
- contains a mixture of different hydrocarbons, mostly alkanes
Describe fractional distillation of crude oil
The different compounds in crude oil are separated by fractional distillation
1) the oil is heated into a gas
2) the gas enters a fractionating column
3) in the column there is a temperature gradient ( hotter at the bottom and cooler at the top)
4) the longer the hydrocarbon the higher it’s boiling point so they condense into liquids and are drained out earlier on
5) the shorter hydrocarbons with lower boiling points condense back into a liquid later at the top and are drained out
6) each drained out fraction of the crude oil contains a mixture of hydrocarbons with similar numbers of carbon atoms and boiling points
What are some uses of hydrocarbons from crude oil
- provides fuel for modern transport ( diesel, kerosene, LPG)
- used as feedstock by the petrochemical industry to make polymers, solvents, lubricants and detergents
What is cracking and describe the 2 process
Cracking splits up a long chained hydrocarbon into 2 smaller ones ( an alkane and an alkene)
- short chained hydrocarbons are more flammable so are use better fuels and are high in demand
- cracking is thermal decomposition reaction ( breaking down molecules by heating)
There are 2 methods:
Catalytic cracking-
1) vaporise the hydrocarbon by heating it
2) pass the vapour over a hot powdered aluminum oxide catalyst
3) the long chain hydrocarbons splits into to shorter chained ones
Steam cracking-
1) vaporise the hydrocarbon by heating it
2) mix the vapour with steam and heat at a very high temperature
3) it will split into 2 shorter chained hydrocarbons
What type of bonds do alkenes have
C=C double bond, unsaturated
What is the formula for alkenes
Cn H2n
What is the order of alkenes starting with 2 carbon atoms to 10 carbon atoms
Ethene C2 H4
Propene C3 H6
Butene C4 H8
Pentene C5 H10
Hexene C6 H12
Heptene C7 H14
Octene C8 H16
Nonene C9 H18
Decene C10 H20
Why are alkenes more reactive than alkanes
Their C=C double bond can open up allowing the 2 carbon atoms to bond with other atoms
Describe the incomplete combustion of alkenes
When burnt in air alkenes tend to undergo incomplete combustion
Alkene + oxygen —> carbon monoxide + carbon dioxide + water (+ energy)
- results in a smoky yellow flame and less energy being released
Balanced equation for incomplete combustion of butene
1) C4 H8 + O2 —> CO + CO2 + H2O
2) C4 H8 + O2 —> CO + CO2 + 4H2O
3) C4 H8 + O2 —> 2CO + 2CO2 + 4H2O
4) C4 H8 + 5O2 —> 2CO + 2CO2 + 4H2O
What is the functional group of alkenes
C=C
What are the 3 addition reactions of alkenes
- Hydrogenation: addition of hydrogen
C4 H8 + H2 —> C4 H10
Forms an alkane with the same number of carbon atoms - Halogens react with alkenes
Ethene + Br2 —> dibromoethane - Steam reacts with alkenes to form alcahol
Ethene + water —> ethanol
What is the test for alkenes
When orange bromine water is added to an alkene it will become colourless
What are polymers
- long molecules formed when lots of smaller molecules called monomers (alkenes) join together
- this reaction is called polymerisation and need high pressure and a catalyst
- plastics are made of polymers
- lots of unsaturated monomers can open up their double bonds and join together to form polymer chains (addition polymerisation)
- many Ethene monomers join together to form poly(Ethene)
- the double bond opens and passes through the brackets, n is moved from the middle left to bottom right
What is the functional group of alcahol
-OH
What is the formula for alcahols
Cn H2n+1 OH
The order of first 10 alcahols
Methanol CH3OH
Ethanol C2H5OH
Propanol C3H7OH
Butanol C4H9OH
Pentanol C5H11OH
Hexanol C6H13OH
Heptanol C7H15OH
Octanol C8H17OH
Nonanol C9H19OH
Decanol C10H21OH
Properties of the first 4 alcahols
- flammable and undergo complete combustion in air (to produce carbon dioxide and water)
- soluble in water to form solutions with a neutral pH
- react with sodium to produce hydrogen
- used in fuels and solvents, ethanol is the main alcohol in alcoholic drinks
Methods of producing ethanol
Ethene + steam —> ethanol
- produces high yield of ethanol
- requires high temperature ( lot of energy)
- ethene comes from non renewable crude oil
Fermentation:
Glucose ——> ethanol + carbon dioxide
Yeast
- uses an enzyme in yeast to convert sugars into ethanol
- occurs in anaerobic conditions
- uses less energy
- glucose is renewable
- the product is aqueous ethanol which needs to be purified by distillation (requires energy)
Reactions of alcohols
- alcahol + sodium forms hydrogen
- alcahol can be oxidised to form carboxylic acid and water
- combustion:
alcohol + oxygen —> carbon dioxide and water
What is the functional group of carboxylic acids
-COOH
(C=O on top and C-OH bottom)
Formula for carboxylic acids
Cn-1 H2n+1 COOH
Carboxylic reactions
- React with carbonates (like any other acid) to form salt, water and carbon dioxide
Ethanoic acid + sodium carbonate —> sodium ethanoate + water + carbon dioxide - react with alcohol (with acid catalyst) to form ester and water
Ethanoic acid + ethanol —> ethyl ethanoate + water
The OH from the carboxylic acid and an H from the alcahol are used to produce the water. - dissolve in water. When they dissolve they ionise and release H+ ions resulting in an acidic solution.
Because they don’t ionise completely not all the acid molecules release H+ ions so they just form weak acidic solutions - aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration
Functional group of esters
-COO-
Properties of esters
- volatile
- distinctive smells
- used as flavourings and perfumes
Properties of polymers
Properties of polymers depend on:
- the monomers used to make it
- the conditions chosen to carry out the reaction
There are 2 types of poly(Ethene):
- one is called high density (HD) and the other low density (LD)
LD:
- using very high pressures and a trace of oxygen, ethene forms LD poly(Ethene)
- the polymer chains are randomly branched and can’t pack closely together
so it has a lower density
HD:
- using a catalyst at 50C and slightly raised pressure, ethene forms HD poly(ethene)
- this is made up of straighter chains. They can pack more closely together so have a higher density and a higher softening temperature
Thermosoftening polymers:
- some polymers will soften when heated then and reset when they cool down
- made up of individual polymer chains tangled together
Thermosetting polymers:
- don’t melt when heated
- have strong covalent bonds forming cross links between the polymer chains
