Organic Chemistry Flashcards
What is a hydrocarbon? What is crude oil?
A compound containing hydrogen and carbon only. Crude oil is a mixture of hydrocarbons
What is a fraction in crude oil?
A part of the mixture with a similar boiling point
What are properties of hydrocarbons if they have longer chains?
- The higher the boiling point
- The higher the viscosity
- The lower the flammability
Why are short chain hydrocarbons more expensive than long chain hydrocarbons?
They are more useful as fuel since they are more flammable
Describe how crude oil is formed
- Millions of years ago when plants and animals which lived in the sea died and fell to the bottom
- Layers of sediment then formed on top of them and their shells and skeletons formed limestone
- The soft tissue was gradually changed by high temperatures and pressures into crude oil
How are hydrocarbons in crude oil separated?
Fractional distillation (physical process)
Describe how fractional distillation works
- The crude oil is heated until it turns into a gas
- Then as it enters the fractional column the gas rises
- However each different fraction has a different boiling point
- Therefore as the gas rises up in the fractioning column, which is gradually cooler, each fraction condenses back into a liquid at different points (where the temperature is lower than their boiling point), separating the crude oil into different fractions
What are the differences between the lab and industrial process of separating crude oil?
LAB -start with a liquid and vaporises one by one and uses -bunsen burner -uses mineral wool -one delivery tube IND: -vapours all (liquid bit bitumen is drained off at the bottom) and then condenses one by one at different temperatures -uses a furnace to heat -no mineral wool -separate tubes for each fraction
How are refinery gases uses (top)?
- Bottles gas
- Domestic heating
- Used in pottery and glass manufacture
How is gasoline (petrol) (second from top) used?
-Fuel for cars
How is kerosine (third from top) used?
- Fuel for jet aircraft
- Domestic heating oil
- ‘Paraffin’ for small heater and lamps
How is diesel oil (gas oil) (fourth from top) used?
- Fuel for buses, lorries, some cars
- Some is also cracked to make other organic chemicals and more petrol
How is fuel oil (fifth from top) used?
- Domestic central heating
- Fuel for big ships
How bitumen used (bottom)?
- Road surfacing
- Asphalt for roofs
What is the order of fractions?
Top to bottom
- Refinery gases
- Gasoline (petrol)
- (Naphtha used in chemical industry as starting material to make plastics, dyes, drugs, explosives, paints)
- Kerosine
- Diesel oil
- Fuel oil
- Bitumen
What are bubble caps in the fractioning column used for?
To stop the separated liquids from running back down the column and remixing
What is a fraction?
A mixture of hydrocarbons with similar boiling points
Why does boiling point increase/become more volatile the longer the chain?
As the chain is bigger, (there is a greater number of) intermolecular attractions (forces) increase and so more heat (energy is needed to overcome them) is needed to break these stronger attractions to produce the widely separated molecules in the gas
Why do the liquids become more viscous the longer the chain?
The more contact points so it is harder for them to slide over each other
Describe Alkanes
They are the simplest homologous series of organic compounds
What is a homologous series?
Compounds in a homologous series have similar chemical properties and show a trend in physical properties
How do you name isomers?
- Count longest side c chain
- Identify side chain
- Identify position of side chains
Describe isomers
They have the same molecular formula but different structural formula
Why do branch chains have lower boiling points than straight chains?
Because there are fewer points of contact with each other and so there are weaker intermolecular forces
Why are alkanes saturated?
Because they contain only single carbon carbon bonds
Why are alkenes unsaturated?
Because they contain a double carbon carbon bond
Why are alkanes unreactive and alkenes more reactive?
- They have a strong carbon-hydrogen bond
- Alkenes are more reactive because they have a double bond which is weaker and hence easier to break
What are the products of complete combustion of alkanes? What are the products of incomplete combustion of alkanes?
- Water and carbon dioxide
- CH4 + 2 O2 –> CO2 + 2H2O - Carbon and carbon monoxide and carbon dioxide and water (+energy) / carbon monoxide and water
- 4CH4 (this is just one possibility, the products depend on how much oxygen is present) + 6O2 –> C + 2CO + CO2 + 8H2O
What causes incomplete combustion?
A lack of oxygen (smoky yellow flame and less energy)
Why is carbon monoxide dangerous?
The carbon monoxide can bind to the haemoglobin in your blood which stops oxygen being carried around your body
What is formed when ethane and bromine react? What is needed for this to happen? What sort of reaction is this?
- Ethane and bromine go to bromoethane and hydrogen bromide
- Brown to colourless
- Substitution reaction
- Needs to be exposed to UV light
- Halogenation
What is the test for alkenes?
- They decolourise bromine water
- When you shake an alkene with orange bromine water, the solution becomes colourless, this is because the bromine molecules, which are orange, are reacting with the alkene to make a dibromoalkane, which is colourless
What happens when an alkene and hydrogen react? What is needed for this reaction? How is this used commercially?
- An alkane is formed
- A nickel catalyst
- To make margarine
What is an addition reaction?
When there are two reactants and one product
What happens when ethane reacts with water?
Ethanol
What is cracking?
- Splitting up long chain hydrocarbons to form shorter chain alkanes and it is a form of thermal decomposition
- Also forms alkenes which are used to make polymers
What conditions are needed for cracking?
- Heat (600-700 degrees Celsius)
- Catalyst (aluminium oxide or silica)
Describe the experiment for cracking in the lab
- Heat the hydrocarbon oil (paraffin?), which is soaked in mineral wool
- After a few seconds move the bunsen burner to heat the aluminium oxide catalyst
- Alternate between the two until the paraffin vaporises and the catalyst glows red
- The heated paraffin vapour cracks as it passes over the heated catalyst
- Small alkanes collect as the end of the boiling tube, while alkene gases travel down the delivery tube
- The alkenes are then collected through water using a gas jar
What are the properties of the products of cracking?
They are more flammable and gases which shows the molecules are smaller than before
What is the point of cracking?
-There is a higher demand for short chains but there is a large amount of long chains
(SC: high demand, low supply) (LC: low demand, high supply)
-5-8 carbon chains are more in demand than 1-4 because the smaller ones are gases and so harder to use, whereas the slightly longer ones can be used in cars and planes
-Fractional distillation of crude oil produces more long-chain hydrocarbons than can be used directly and fewer short-chain hydrocarbons than required
What is a polymer?
A long chain molecule formed from repeating identical monomer units
How are addition polymers formed?
- By joining up many small molecules called monomers
- The monomers that make up addition polymers have a carbon carbon double bond (they are alkenes)
- Under high pressure and a catalyst, many small molecules open up the double bond and polymerise to form very long saturated chains (polymers)
What are three examples of polymers? Are their physical properties the same?
- Polyethene
- Polypropene
- Polychloroethene
Different polymers have different physical properties, which makes them suitable for various different uses
What are the uses of Polyethene?
- It is light, stretchable polymer
- This makes it ideal for making packaging such as plastic bags, bottles and other containers
What are the uses of Polypropene?
- Very tough polymer, but it is relatively flexible and resistant to heat ((does not soften in boiling water) and resistant to chemicals)
- It is used to make things like kettles, food containers and carpets (ropes, plastic crates)
What are the uses of Polychloroethene?
- Flexible, some ridgity, electrical insulator
- Used to make clothes and pipes and for insulating electrical cables, (drainpipes, plastic window frames, clothing, electrical insulation)
How do you get rid of polymers?
- Most (addition?) polymers are hard to get rid of
- Most (addition?) polymers are inert, because of the carbon carbon bonds in the polymer chain and very strong and aren’t easily broken
- This means that it takes a very long time for addition polymers to biodegrade (be broken down by bacteria or other organisms), if you bury them in a landfill site they will still be there years later
- Burning plastics can release toxic gases
- So best thing to do is reuse them and then recycle them
Describe the hydration of ethene, what catalyst is used? What pressure is used? What temperature is needed?
- Passing ethene and steam over a phosphoric acid catalyst
1. Ethene is produced by cracking
2. Ethene reacts with steam to make ethanol
3. The reaction needs a temperature of 300 degrees Celsius and a pressure of 60-70 atmospheres
4. Phosphoric acid is used as a catalyst
5. Non renewable starting material (crude oil)
6. Rapid and continuous flow process
7. Very pure yield close to 100%
Describe fermentation, what temperature is needed?
- Fermentation of sugars, for example glucose
1. The raw material is renewable and good for poorer countries, sugar. This is converted into ethanol using yeast (sugar cane)
2. This process needs a low temperature 30-40 degrees Celsius and left for several days in the absence of air
3. Slow reaction
4. Batch process
5. Isn’t very concentrated ethanol (as yeast is killed if mixture contains more than 15% ethanol)
6. So it needs to be purified by fractional distillation to separate the water and ethanol but even so some water remains in the final product and the maximum purity is 96% ethanol
What are the advantages and disadvantages of using fermentation?
- ADV: Sugar renewable resource, low temp and pressure so cheaper, cheaper equipment but high labour cost
- DIS: Very slow, very impure, batch process
What are the advantages and disadvantages of using hydration of ethene?
- ADV: Very fast, continuous flow process, very pure product
- DIS: Ethene from crude oil finite resource, high temp and pressure so expensive (and ex. equipment) but low labour costs
How is ethanol dehydrated to form ethene? What sort of reaction is this? What catalyst is needed?
- This is done by removing water from the ethanol in a dehydration reaction
- ELIMINATION REACTION - Ethanol vapour is passed over a hot catalyst of aluminium oxide, the catalyst provides a large surface area for the reaction
In the dehydration of ethanol why was the first tube of gas discarded?
Because it was full of air from the boiling tube and not the gas
Describe global warming and the greenhouse effect
- The products of combustion of a hydrocarbon such as methane are carbon dioxide and water
- Carbon dioxide is a greenhouse gas, the greenhouse effect may be causing global warming
Describe the effects of incomplete combustion and global dimming
- When a hydrocarbon is burnt in a limited supply of oxygen, carbon monoxide may be formed which is toxic to humans
- Or particles of carbon called soot may be formed, and these particles may collect in the atmosphere and reflect sunlight back into space and this is called global dimming
- Global dimming may lead to the cooling of the earth and can mask the effects of global warming
Describe photochemical smog and where it forms?
- In a car engine, the temperature is high enough that the nitrogen and oxygen from the air react to from nitrogen oxides
- There react in the air with hydrocarbons to form a photochemical smog
- This can lead to poor air quality and respiratory diseases
Describe Acid rain and how it is formed
- If sulphur is present in fuels, sulphur dioxide may form when they are brunt
- This dissolves in water droplets in the atmosphere to from sulphuric acid
- This can cause damage to plants (kills trees), animals (can die), lakes (become acidic) and limestone buildings
- Nitrogen oxides dissolve in water to form acid rain too and nitrogen oxides are formed when the temperature is high enough for the nitrogen and oxygen in the air to react, which often happens in car engines. Nitrogen oxides include nitrogen dioxide and nitrogen monoxide
- Nitrogen oxides and sulphur dioxide are pollutant gases
How can we reduce pollution?
- A catalytic converter can be used to remove carbon monoxide and nitrogen monoxide from a car’s exhaust
- In power stations sulphur dioxide is removed from the flue gases by reacting it with calcium carbonate
- This is called flue gas desulphurisation
What are the main fractions obtained from crude oil?
- Refinery gases
- Gasoline
- Kerosene
- Diesel
- Fuel oil
- Bitumen
What is the trend in boiling point and viscosity of the main fractions?
-Higher viscosity and boiling point lower down (toward bitumen)
What is produced from the incomplete combustion of fuels? Why is this dangerous?
- Carbon monoxide
- Poisonous because it reduces the capacity of the blood to carry oxygen, colourless and odourless
What is condensation polymerisation? What is an example of a condensation polymer? What is an example of a small molecule that condensation polymerisation produces as well as the polymer?
- Condensation polymerisation usually involves two different types of monomer
- The monomers react together and bonds form between them, making polymer chains
- For each new bond that forms, a small molecule (for example water) is lost
- Nylon is an example of a condensation polymer
What does the term general formula mean?
Shows the ratio of elements in a homologous series
What is an isomer?
They have the same molecular formula but a different structural formula
What is the general formula for alkanes?
CnH2n + 2
What happens when ethene and bromine react? What sort of reaction is this?
- Halogens react with alkenes to make haloalkanes
- Dibromoethane
- Addition reaction
What is the general formula for alkenes?
CnH2n
What is the trend in boiling point and viscosity of the main fractions?
The longer the chain, the higher the boiling point and viscosity (nearer the bottom)
