Unit 8- Environmental Chemistry

Question 1

Alkanes

Answer 1

• found in crude oil
• contain single bonds only
• ‘saturated’ hydrocarbons
• petrol is mostly a mixture of alkanes

Question 2

Fractional distillation

Answer 2

• crude oil is vaporised at 350°c and put through a fractionating column
• longest chains form residue at the bottom
• mineral oil condenses at 340°c
• diesel condenses at 250°c
• kerosene condenses at 180°c
• naptha condenses at 110°c
• petrol condenses at 40°c
• shortest chains escape out the top as gasses at room temp

Question 3

Types of cracking

Answer 3

• used to make long fractions into multiple more useful short fractions by breaking the C-C bond in alkanes
• Thermal cracking uses high temp (1000C), high pressure (70atm) and produces lots of alkenes for polymerisation
• Catalytic cracking uses Zeolite catalyst, less high pressure (500C), slight press. is faster, cheaper, and produces aromatic hydrocarbons and alkanes

Question 4

combustion

Answer 4

• Complete combustion forms CO2 and Water
• The internal combustion engine uses alkanes as fuel and produces pollutants like nitrous oxides and CO and C. If the hydrocarbon had sulfur impurities it also produces SO2
• Incomplete combustion produces Soot, CO and CO2, and water
• can not tell exact molecular amounts for incomplete combustion so just guess
• soot causes breathing problems and CO is poisonous but can be removed by catalytic converters

Question 5

pollution

Answer 5

• N and O react under high pressures/temp to make NO and NO2. These make ground level Ozone which is an irritant
• sulfur dioxide forms from impurities in fuel, and causes dilute sulfuric acid to form when it dissolves into cloud moisture, which is acid rain that kills crops
• SO2 can be removed by powdered CaO in water making CaSO3
• CO2 causes global warming

Question 6

Catalytic converters

Answer 6

• NO, unburnt Hydrocarbons and CO are removed with these equations
• Hydrocarbon + 02 -> xCO2 + yH2O
• 2NO -> N2 + O2
• 2NO + 2CO -> N2 + 2CO2

Question 7

Global Warming

Answer 7

• greenhouse gasses escape into atmosphere and are trapped
• absorb IR energy reflected off the earths surface and reflect some back
• carbon neutral fuels don’t add any CO2 to atmosphere due to following reactions (eg fermented Ethanol)
• 6CO2 + 6H2O -> C6H12O6 +3O2 (photosynthesis)
• C6H12O6 -> 2C2H5OH + 2 CO2 (fermentation)
• 2C2H5OH -> 4CO2 + 6H2O (combustion)

Question 8

Halogenoalkanes

Answer 8

• methane reacts with chlorine in a free radical substitution reaction to produce a halogenoalkane