2: Alkanes and Pollution
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What is an alkane?
A saturated hydrocarbon.
Describe how fractional distillation works.
The crude oil is vapourised. The hydrocarbons start to evaporate. The short chain hydrocarbons evaporate first, condense and are drained off, but the long chain hydrocarbons have a high boiling point and take longer to evaporate. Some remain as a viscous liquid.
List the 9 crude oil fractions in order from lowest to highest boiling point.
Liquefied Petroleum Gas Petrol Naphtha Kerosene Diesel Lubricating Mineral Oil Fuel Oil Wax and Grease Bitumen
What is cracking and why is it done?
Splitting long chain hydrocarbons into short chains because they are more useful.
Give an equation for the cracking of decane into 2 products.
Decane -> Ethene + Octane
Give an equation for the cracking of decane into 3 products.
Decane -> Ethane + Pent-2-ene + Propene
Name 2 types of cracking.
Thermal and Catalytic.
What temperature and pressure does thermal cracking use?
1000C and 70 atm.
What types of molecules does thermal cracking mostly create? What are these products useful for making?
Alkenes. Useful for making polymers.
Name the catalyst used in catalytic cracking.
Zeolite catalysts.
Broadly state the pressure and give the temperature for catalytic cracking.
Slight pressure, high temperature of 500C.
What is complete combustion?
There is sufficient O2, so the molecule is completely burned so CO2 and water is produced.
Give an equation for complete combustion of C3H8.
C3H8 + 5O2 -> 3CO2 + 4H2O
What is incomplete combustion?
There’s not enough oxygen so the molecule doesn’t burn properly.
Give and equation for incomplete combustion of C3H8.
C3H8 + 3.5O2 -> 3CO + 4H2O
Why can incomplete combustion be dangerous?
It produces carbon monoxide.
What are the issues with CO production?
It irreversibly binds to haemoglobin in the blood, meaning you cannot get enough oxygen into the body.
How are toxic exhaust gases removed from cars?
Using catalytic converters.
How is nitrogen monoxide produced?
High pressures and temperatures in car engines cause nitrogen and oxygen atoms in the air to react.
Give 2 equations to show how nitrogen can lead to production of nitrogen dioxide.
N2 + O2 -> 2NO 2NO + O2 ->2NO2
What could be produced when nitrogen oxides react with hydrocarbons in the presence of sunlight?
Ground level ozone.
How can ground level ozone affect the human body?
Respiratory issues, lung damage, eye irritation etc
Give an equation for the decomposition of NO in a catalytic converter.
2NO -> N2 + O2
Give an equation for the decomposition of NO and CO in a catalytic converter?
2NO + 2CO -> N2 + 2CO2