2: Alkanes and Pollution Flashcards
Fractional Distillation Thermal + Catalytic Cracking Incomplete + Complete Combustion Nitrous Oxides Ground Level Ozone Catalytic Converters Sulfur Dioxides and Flue Gases Acid Rain
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
How can sulfur dioxide and nitrogen dioxide gas affect the atmosphere?
Sulfur and nitrogen dioxide can dissolve in moisture and be converted to sulfuric/nitric acid, leading to acid rain.
How does acid rain affect the environment?
Destroys vegetation, corrodes buildings and kills fish in lakes.
Describe how sulfur dioxide gas can be removed from flue gases using calcium carbonate/calcium oxide.
CaCO3 or CaO is mixed with water to make an alkaline slurry. When the flue gases mix with this slurry, the acidic SO2 gas reacts with calcium compounds to form calcium sulfate.
Give an equation for the removal of SO2 from flue gases.
CaO + SO2 -> CaSO3
How does the greenhouse effect work to keep the earth warm?
Greenhouse gases absorb infrared and emit some energy back to earth, keeping it warm.
Explain how oxides of nitrogen are formed in engines.
Nitrogen and oxygen from the air react as a result of high temperatures created by engines.
State why it is desirable to decrease emissions of oxides of nitrogen from vehicles.
Nitrogen oxides lead to production of acid rain.
