Topic 7- Hydrocarbons and Crude Oil and organic compounds Flashcards
What is organic chemistry?
Organic chemistry is the study of substances that contain carbon atoms.
Why is this branch of chemistry known as Organic Chemistry?
All living things are made up from carbon compounds, and so this branch of chemistry was historically known as organic chemistry (organic = made from plants and animals).
The main source of organic compounds are living, or once or once living materials from plants and animals. However it has been discovered that these carbon compounds could also be made in the lab from non-living materials-chemicals.
Name one source of carbon compounds
These sources include fossil fuels which are a major source of feedstock (fuel) for the petrochemical industry.
Unrefined crude oil is a fossil fuel often used.
Why is the study and practice of organic chemistry important?
Because chemists are able to take organic molecules and modify them in many ways to make new and useful materials such as polymers, perfumes, flavourings, dyes, detergents and medicines.
Where is crude oil found?
Crude oil is a finite resource found under the ground in rocks.
What is crude oil made from?
Crude oil is the remains of dead plants and animals mainly consisting mainly of plankton that was buried in mud.
What is the structure of crude oil?
Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydro carbons.
What is a hydrocarbon?
A hydrocarbon is any molecule that contains hydrogen and carbon atoms only. So C10 H22 (decade, an alkane) is a hydrocarbon, but CH3 COOC3 H7 (an ester) is not- it contains oxygen.
How are hydrocarbons structured?
Each carbon atom must have 4 covalent bonds and each hydrogen must have 1 covalent bond.Image result for hydrocarbon methane structure
What are most of the hydrocarbons in crude oil called?
Most of the hydrocarbons in crude oil are called alkanes.
What are alkanes?
1) Alkanes are the simplest type of Hydrocarbon you can get. They have the general formula Cn H2n+2.
2) The alkanes are a homologous series:
- A group of organic compounds that share a general formula.
- Have similar chemical properties, so react in a similar way.
3) Alkanes are saturated compounds- each carbon atom forms four single covalent bonds.
What is a homologous series?
In organic chemistry, a homologous series is a series of compounds with the same general formula.
A homologous series is a family of hydrocarbons with similar chemical properties so react similarly.
What does saturated mean?
In organic chemistry, a saturated compound is a chemical compound that has a chain of carbon atoms linked together by single bonds. Saturated hydrocarbons are called alkanes.
What are the first four alkanes called?
1) Methane
2) Ethane
3) Propane
4) Butane
How can alkane molecules be represented?
Alkane molecules can be shown:
- Using their molecular formula
- Displayed formula (a drawing showing all the atoms and bonds in a molecule)
What affects the properties of hydrocarbons? And what 3 things does this effect?
The more carbon atoms a hydrocarbon molecule has, the longer, larger and heavier it will be. This will affect its physical properties:
- Boiling Point. Longer molecules have a higher boiling point because they are heavier, move more slowly, become tangled, have greater intermolecular forces and therefore require more heat energy to gain enough speed/energy to leave the surface of the liquid to become a gas, i.e. boil/evaporate.
- Flammability. Smaller (weaker) molecules burn more easily e.g. methane, butane or octane. Larger molecules do not tend tend to burn, e.g bitumen-you can’t easily set fire to the road! Therefore, the smaller hydrocarbons tend to be used as fuels.
*Viscosity (thickness): Longer molecules become more tangled, possess greater intermolecular forces and are less able to move past each other-compare octane (8 carbons clumped together like pasta) and bitumen (120 carbons tangled like spaghetti).
The shorter the molecules, the more runny the hydro carbon is- that is, the less viscous it is.
What is fractional distillation?
Fractional distillation is a technique used to separate hydrocarbons into fractions, each of which contains molecules with a similar number of carbon atoms.
Fractions being the individual hydrocarbons, distillation being the process of purifying a substance via heating and cooling.
Why is fractional distillation an important technique?
As a mixture, crude oil is not useful, but if we separate it into fractions i.e. groups of hydrocarbons of similar size, from the smallest to the largest, we have a very useful collection of molecules, which can be further processed to produce FUELS for cars, lorries etc and FEEDSTOCK for the PETROCHEMICAL INDUSTRY, and to make medicines, plastics, etc.
How does separation of hydrocarbons occur? (Do not learn this, just understand)
1) The oil is heated until most of it has turned into gas. the gases enter a fractionating column (and the liquid bit is drained off).
2) In the column there is a temperature gradient ( it’s hot at the bottom and cooler as you go up).
3) The longer hydrocarbons have high boiling points. They condense back into liquids and drain out of the column early on, when they’re near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it’s cooler.
4) You end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points.
Explain the process of fractional distillation. (previous exam question, LEARN!)
The crude oil is HEATED to EVAPORATE hydrocarbons to vapour. The different hydrocarbons COOL and CONDENSE at different temperatures because they have different boiling/condensation points. This is because there is a TEMPERATURE GRADIENT in the chamber.
In summary:
- Crude oil is heated
- to evaporate hydrocarbons
- there is a temperature gradient in the chamber
- so fractions condense
- at different levels
What fuels are produced from crude oil?
Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefield petroleum gases, are produced from crude oil.
What useful materials on which modern life depends are produced by the petrochemical industry?
-Solvents -Lubricants -Polymers -Detergents
How are there so many natural and synthetic carbon compounds?
The vast amounts of carbon compounds is due to the ability of carbon atoms to bond together to form different groups called homologous series.
Alkanes, alkenes, as well as other families such as alcohols and carboxylic acids, are all examples of different homologous series.
What is complete combustion?
Hydrocarbons contain H and C atoms. When complete combustion occurs, the hydrogen is oxidised(combined with oxygen) to form water, H2O and the carbon is oxidised to form carbon dioxide, CO2. Energy in the form of heat and light is released.
What is the equation for complete combustion of a hydrocarbon?
hydrocarbon + oxygen ——-> carbon dioxide + water vapour
What is an Alkene?
What is the general formula of an alkene?
1) Alkenes are HYDROCARBONS with a DOUBLE COVALENT BOND between two of the CARBON atoms in their chain.
2) The C=C double bond means that alkenes have two fewer hydrogens compared with alkanes. This makes them UNSATURATED.
3) The C=C double bond can open up to make a SINGLE BOND, allowing the two carbon atoms to bond with OTHER ATOMS. This makes alkenes REACTIVE - far more than reactive than other ALKANES.
4) The first 4 alkenes are ethene (2 carbon atoms), propene (3 Cs), butene (4 Cs) and pentene (5Cs).
- Like alkanes, they form a homologous series, each differing by a CH2 unit. They have a general formula C2H2n.
N.B. There is no such thing as methene- because it cannot contain a double bond.
How reactive are alkenes with bromine water?
Do alkenes react with other alkenes?
Alkenes are more reactive than alkanes, reacting with bromine to make a colourless bromine water.
Alkenes can also react with other alkenes to make polymers (plastics). Alkenes are also useful starting materials for other chemicals and medicines.
How reactive are alkanes with bromine water?
Why is the bromine water test used?
Alkanes are very un-reactive and will not make the bromine water colourless.
The bromine test is used to distinguish alkanes from alkenes. ALKENES DECOLOURISE BROMINE WATER.
Which hydrocarbon fractions are in greatest demand?
The fractions containing smaller hydrocarbons tend to be used as fuels (e.g. heptane, C7H16, is a major component of gasoline/petrol), whilst the larger hydrocarbons are used for surfacing roads (e.g. bitumen, C120H242).
The global DEMAND for FUEL is HIGH, meaning that there is a shortage of SHORT HYDROCARBONS and an excess of long/large hydrocarbons. The solution to the problem is to convert large molecules into smaller molecules.
What is cracking?
- SHORT-CHAIN HYDROCARBONS are flammable so make good fuels and are in HIGH DEMAND. LONG-CHAIN hydrocarbons form thick gloopy liquids like TAR which aren’t all that useful, so…
- A lot of the LONGER alkane molecules produced from fractional distillation are SPLIT and turned into smaller, more USEFUL ones by a process called CRACKING.
So cracking is a thermal decomposition reaction because large alkanes are heated to a vapour and broken up (decomposed) into smaller molecules.
What products are formed during the process of cracking?
DURING CRACKING A MIXTURE OF ALKANES AND ALKENES IS ALWAYS MADE. Some of the products of cracking are useful as fuels, e.g. petrol for cars and paraffin as jet fuels
What is the use of Alkenes?
Alkenes are used to produce polymers and as starting materials for the production of many other chemicals.
What are the different methods of cracking?
*Cracking is a thermal decomposition reaction-breaking molecules down by heating them.
- There are two methods of cracking:
- Catalytic cracking (A)
- Steam cracking(B)
A
1)For catalytic cracking the first step is to heat long-chain hydrocarbons at very hight temperatures to vaporise them (turn them into gas). In industry this would take place in a cracking unit next to a fractional distillation column.
2) Then the vapour is passed over a hot powered aluminium oxide catalyst.
3) The long-chain molecules split apart on the surface of the specks of catalyst.
In the laboratory, a much simpler set up is more usual. The porcelain chips act as a catalyst. The alkane used here is a paraffin, each molecule containing approximately 20 carbons
B
You can also crack hydrocarbons if you vaporise them, mix them with steam and then heat them to a very high temperature. This is known s steam cracking.
What is a functional group?
A functional group is an atom or atoms that is responsible for most of the chemical reactions of an organic compound.
What is the functional group of alkenes?
All alkenes have the functional group C=C, so they all react in similar ways. So you can suggest the products of a reaction based on your knowledge of how alkenes react in general.
Are alkenes a homologous series?
Yes, because they have the same functional group and react in similar ways.
How do alkenes react?
Most of the time alkenes react via ADDITION REACTIONS. The carbon double bond C=C will open up to leave a SINGLE BOND and a new atom is added to each carbon.
How do alkenes react with oxygen?
1) Alkenes can react with a large amount of oxygen in COMBUSTION (burning) reactions, just like alkanes. When a large amount of oxygen is present they COMBUST COMPLETELY to produce only water and carbon dioxide.
2) However we do not generally combos alkenes as there isn’t enough oxygen in the air for this, so when you burn them they tend to undergo INCOMPLETE COMBUSTION.
3) We don’t combust alkenes for 2 reasons:
- when combusted carbon dioxide and water are still produced, but you can also get carbon and monoxide (carbon produces soot).
alkene+oxygen=carbon +carbon monoxide +CO2+H2O
-Incomplete combustion results in a smoky yellow flame, and less energy being released compared to complete combustion of the same compound.
How do alkenes react with hydrogen?
- Alkenes are unsaturated i.e. not yet full up with hydrogen atoms-there is space to add more at the C=C double bond. Alkanes, oppositely are known as saturated (full up) as they can’t fit more hydrogens onto their single bonds. When hydrogen is added to an unsaturated alkene, a saturated alkene is made.
- The reaction is called a hydrogenation (hydrogen is added).
- Occurs at 150 degrees celsius.
- A nickel catalyst must be present.
How do alkenes react with halogens?
1) Alkenes will also react in ADDITION REACTIONS with HALOGENS such as bromine, chlorine and iodine.
The molecules formed are saturated, with C=C carbons each becoming bonded to a halogen.
2)For example, bromine and ethene react together to form dibromoethane: There are two bromine atoms so it’s called DIbromoethane.
Remember the addition of bromine to a double bond can be used to test for alkenes:
1) When orange BROMINE WATER is added to a SATURATED COMPOUND, like an ALKANE, no reaction will happen and it’ll stay BRIGHT ORANGE.
2) If it’s added to an ALKENE the BROMINE will add across the double bond making a COLOURLESS dibromo-compound-so the bromine water is decolourised.
How do alkenes react with water (steam)?
- Alkenes react with STEAM by an addition reaction whereby OH and H of water are added across the C=C double bond and an ALCOHOL is produced.
- It is called a hydration action.
- HIGH TEMPERATURES and HIGH PRESSURES are required, in addition to a CONCENTRATED PHOSPHORIC ACID CATALYST.
What are alcohols?
The alcohols are a group of compounds that make up an homologous series all containing the functional group -OH.
It follows an homologous series whereby each member differs from its neighbour by a CH2 unit.
What is the general formula of an alcohol?
The general formula for an alcohol is CnH2n+1OH. So an alcohol with two carbons has the formula C2H5OH.
What is the naming system of alcohols?
The basic naming system of alcohols is the same for alkanes-but you replace the final ‘e’ with ‘ol’.
What are the names of the first 4 alcohols?
1) Methanol (1 carbon)
2) Ethanol (2 Cs)
3) Propanol (3 Cs)
4) Butanol (4Cs)
What are the properties of alcohols?
- The first four alcohols have similar properties.
- Alcohols are FLAMMABLE. They undergo complete combustion in air to produce CARBON DIOXIDE and WATER.
- Methanol, ethanol, propanol and butanol are all soluble in water. Their solutions have a NEUTRAL pH.
- They also react with SODIUM. One of the products of this reaction is HYDROGEN.
- ALCOHOLS can be OXIDISED by reacting with oxygen (e.g. from the air) to produce a CARBOXYLIC ACID.
- Different alcohols form different carboxylic acids. For example, METHANOL is oxidised to METHANOIC ACID, while ethanol is oxidised to ethnic acid.
