Alkanes Flashcards
What are alkanes?
- Alkanes are saturated hydrocarbons.
General formula for alkanes
CₓH₂ₓ₊₂
General formula for cycloalkanes. Are they saturated hydrocarbons?
-CₓH₂ₓ
Yes, they are saturated hydrocarbons (as there are no C=C double bonds.)
() - extra info for clarification.
What is another word for crude oil?
- Petroleum.
What is crude oil/ petroleum?
- Mixture of different length hydrocarbons- mainly alkane hydrocarbons.
How can hydrocarbons in petroleum/ crude oil be separated? What are the stages of this separation?
- By fractional distillation.
1.) Crude oil vapourised
2.) Vapourised oil enters column and rises.
3.) Column has temperature gradient. As vapour rises, parts of mixture condense at different temperatures.
4.) This is because there are different chain lengths - hence, different boiling points.
5.) The fractions are drawn off at different levels.
What happens to the longest and shortest hydrocarbons during fractional distillation?
- Longest hydrocarbons: don’t vapourise and run down to bottom of column.
- Shortest hydrocarbons: won’t even condense at top of column; so come off as a gas at top of column.
What is cracking?
- Cracking is breaking a longer chain alkane into shorter hydrocarbons.
- It involves breaking the C-C bond in alkanes.
Why is cracking useful?
- Because shorter hydrocarbons are in higher demand than longer hydrocarbons - as they are used as fuel.
What are the two different types of cracking?
- Thermal cracking
- Catalytic cracking.
What are conditions for thermal cracking? What does thermal cracking produce predominantly? Why is the product useful ?
- High temperature and high pressure required: 1000⁰C/ 70 atm
- Thermal cracking produces a high percentage of alkenes - useful as alkenes can be used to make polymers (ie. plastics.)
What are the conditions for catalytic cracking?
- High temperature of 450⁰C
- Slight pressure
- Zeolite catalyst
What is the role of the zeolite catalyst in catalytic cracking?
- Helps lower the temperature and pressure needed for cracking to occur.
- This lowers the cost and speeds up the process.
What are the main products of catalytic cracking?
- Aromatic hydrocarbons (useful in fuels in vehicles) and motor fuels.
What are alkanes predominantly used as, and why?
- Alkanes are used as fuels because most burn readily to produce large amounts of energy.
What are the products for the complete combustion of alkanes?
Carbon dioxide + water
True or False
Only the combustion of ALKANES (specifically) can be either complete or incomplete.
- False.
- Combustion of alkanes AND other organic compounds can be complete or incomplete.
What is complete vs incomplete combustion?
- Complete: fuel burns in plentiful supply of oxygen.
- Incomplete: fuels burns in limited supply of oxygen.
What are the products for incomplete combustion of alkanes?
- Carbon monoxide - CO(g)
- Carbon soot - C(s)
- Unburned hydrocarbons
What is the issue with carbon monoxide (CO)? How can CO be removed from exhaust fumes in the engine?
- CO is poisonous as it binds to haemoglobin in the blood, preventing oxygen binding.
- CO can be removed using a catalytic converter.
3 problems associated with carbon soot.
1.) Causes breathing problems.
2.) Makes buildings dirty
3.) Clogs up engines.
How is increase in carbon dioxide affecting the environment and HOW?
- Causing global warming.
- Carbon dioxide = greenhouse gas: absorbs infrared radiation from sun/ emitts some of it back into Earth, this is called greenhouse effect.
- All greenhouse gases CONTAIN polar bonds.
How are oxides of nitrogen (NOx) formed/ made?
- Oxygen and nitrogen (naturally in the air) combine/ react due to high pressures and temperatures in car engines.
Give 4 poulltants produced from the internal combustion engines.
1.) NOx (oxides of nitrogen.)
2.) CO
3.) Carbon (soot)
4.) Unburned hydrocarbonds.
What do catalytic converters do?
- Catalytic converters remove gaseous pollutants from internal combustion engines.
- Reduce amount of unburnt hydrocarbons, oxides of nitrogen going into atmosphere/ STOP CO from entering the atmosphere.
What is ozone? Where does it occur? What is the issue with ozone?
- Ozone occurs in lowest level of atmosphere.
- Sunlight, hydrocarbons and nitrogen dioxide mix to form ozone.
- Ozone is toxic to humans.
How is photochemical smog formed?
- Solid carbon soot and ozone mix to make photochemical smog.
What does combustion of hydrocarbons containing sulphur lead to?
- Combustion of hydrocarbons containing sulphur leads to sulphur dioxide - that causes air pollution/ acid rain.
How does sulphur dioxide actually cause acid rain? What other gases will cause acid rain like sulphur dioxide does?
- Sulphur dioxide = acidic gas.
- Reacts with water vapour (in atmosphere) to form sulphuric acid/ acid rain.
- Oxides of nitrogen will cause acid rain like sulphur dioxide does.
What 3 main problems does acid rain cause?
1.) Causes damage to plants.
2.) Kills fish
3.) Causes erosion of buildings.
How do you remove sulphur dioxide from flue gases in factories? What is this process called?
- Process called: wet-scrubbing.
- Alkali - calcium carbonate/ oxide- will be dissolved in water and sprayed on acidic sulphur dioxide gas, neutralising the sulphur dioxide.
What are the different fractions collected by fractional distillation? Give the order the different fractions are collected in, starting from the top- working you way down the column.
Neumonic to remember?
1.) LPG: liquid petroleum gases.
2.) Petrol/ Gasoline
3.) Naptha
4.) Kerosene
5.) Diesel oil
6.) Fuel oil
7.) Bitumen
Lazy Penguings, Never Keep drinking flipping beer.
What are the different uses for all the fractions obtained from crude oil by fractional distillation?
1.) LPG –> Bottled gases (ie. stove gases.)
2.) Petrol/ Gasoline –> fuel for cars
3.) Naptha –> used in petrochemical industry e.g., paints.
4.) Kerosene –> jet fuel
5.) Diesel oil –> fuel for vans/ lorries
6.) Fuel oil –> fuel for ships.
7.) Bitumen –> used for road surfacing.
Definition of “fraction” formed in fractional distillation.
- Fraction is a mixture of compounds with similar boiling points.
June 2023 Paper 2 AS
Explain why water should enter the condenser at the bottom and not at the top.
- Ensures that the condenser fills with water.
- Ensuring more vapours condense.
2016 Paper 2 AS
Platinum, rhodium, palladium are metals used inside catalytic converters. Very thin layer of metals is used on honeycomb ceramic support.
Explain why thin layer is used in this way.
- Increases surface area.
- Reduces amount of metal needed.
june 2016 paper 2 AS
Write an equation to show how CO and NO react in a catalytic converter
2CO + 2NO –> 2CO2 + N2.
