organic chemistry Flashcards
What is crude oil?
Crude oil is a finite resource found in rocks formed over millions of years from the remains of ancient biomass (mainly plankton buried in mud). It is a mixture of a very large number of compounds, most of which are hydrocarbons, most being alkanes. The hydrocarbons each have a different boiling point.
What are hydrocarbons?
Hydrocarbons are molecules made up of hydrogen and carbon atoms only.
What are alkanes?
Alkanes are a hydrocarbon with general formula CnH2n+2.
Give the molecular formula and name when there is an alkane and n=1.
methane - CH4
Give the molecular formula and name when there is an alkane and n=2.
ethane - C2H6
Give the molecular formula and name when there is an alkane and n=3.
propane - C3H8
Give the molecular formula and name when there is an alkane and n=4.
butane - C4H10
Are alkanes saturated or unsaturated molecules? Why?
Alkanes are saturated molecules as the carbon atoms are fully bonded to hydrogen atoms.
As the size of the alkane increases, what happens to the viscosity?
As the size of the alkane increases, the molecules become more viscous.
What does viscosity mean?
Viscosity means the thickness of a fluid.
As the size of the alkane increases, what happens to the flammability?
As the size of the alkane increases, the molecules become less flammable.
As the size of the alkane increases, what happens to the boiling points?
As the size of the alkane increases, the boiling points increase. (methane –> butane are gases at room temperature)
What three things run on hydrocarbon fuels?
Ships, planes and cars run on hydrocarbon fuels.
What is complete combustion?
Hydrocarbon fuels release energy when they are combusted. During combustion, the carbon and hydrogen atoms react with oxygen (oxidised). If the oxygen is unlimited, the reaction produces CO2 and H2O, which is complete combustion.
Give the complete combustion of methane.
complete combustion of methane:
methane + oxygen –> carbon dioxide + water
CH4 + 2O2 –> CO2 + 2H20
What needs to happen for the hydrocarbons in crude oil to be useful?
In order or the hydrocarbons in crude oil to be useful, we have to separate them by fractional distillation.
Describe the process of fractional distillation in terms of crude oil.
fractional distillation of crude oil:
- crude oil is separated into fractions, each containing hydrocarbons with a similar number of carbon atoms
- the crude oil is heated to a very high temperature, causing it to boil
- all of the hydrocarbons turn into a gas
- they condense when they reach their boiling point and are removed
In the fractional distillation of crude oil, when are long chain hydrocarbons removed?
Very long chain hydrocarbons have very high melting points, so they are removed near the bottom of the column.
In the fractional distillation of crude oil, when are short chain hydrocarbons removed?
Very short chain hydrocarbons have very low boiling points, so they are removed near the top of the column as a gas as they don’t condense.
Give five products of the fractional distillation of crude oil and what they’re used for.
products of crude oil:
- petrol and diesel are used in cars
- kerosene is used as jet fuel
- heavy fuel oil is used in ships
- liquefied petroleum gas (LPG) is used in camping stoves
Give five products of the fractional distillation of crude oil and rate the boiling points from highest to lowest.
products of crude oil boiling points: HIGHEST heavy fuel oil petrol kerosene diesel liquefied petroleum gas (LPG) LOWEST
What is LPG?
LPG is liquefied petroleum gas, a product of the fractional distillation of crude oil and has a very low boiling point. It contains mostly propane and butane.
What can some fractions from the fractional distillation of crude oil be used to make?
Some fractions are used as feedstock (a chemical used to make other chemicals) for the petrochemical industry. It can be used to make solvents, lubricants, detergents and polymers.
What is cracking?
Cracking is when a large alkane is broken down (cracked) into smaller, more useful molecules.
What are the products of cracking?
products of cracking:
- shorter chain alkanes are used in fuels
- alkenes (another kind of hydrocarbon)
What are the two kinds of cracking?
types of cracking:
- catalytic cracking - use heat and a catalyst, which both speed up the reaction
- steam cracking - use heat and steam
What is an alkene?
An alkene is a hydrocarbon that has at least one carbon to carbon double bond. They have general formula CnH2n.
Are alkene molecules saturated or unsaturated? Why?
Alkene molecules are unsaturated as the alkenes have fewer hydrogen atoms than the alkane with the same number of carbon atoms.
Which is more reactive: alkenes or alkanes?
Alkenes are more reactive than alkanes.
Why are alkenes useful?
Alkenes are useful as they can be used to make polymers and other chemicals.
What is the test for alkenes and alkanes?
test for alkenes:
- add bromine water, shake it, the solution will turn colourless
test for alkanes:
- add bromine water, shake it, the solution will remain the same colour
Give the molecular formula and name when there is an alkene and n=2.
ethene - C2H4