3.3.2 Alkanes Flashcards
What are alkanes?
Saturated hydrocarbons
What is the polarity of Alkanes?
Non-polar, as only intermolecular force is weak van der walls.
As the chain length increases what happens to force of van der walls?
Increases as there are more electrons
What is the solubility of Alkanes and why?
Insoluble in water but soluble in non-polar solvents because water has strong hydrogen bonds that are stronger than van der walls. So Alkanes can not overcome the force of attraction between water molecules
Describe the process of fractional distillation.
Crude oil heated in furnace
A mixture of liquid and vapour passes into a tower which is cooler at top than bottom
Vapour moves up the tower via a series of trays which contain bubble caps until they arrive at a tray that is cool enough. Condense here
Mixture of liquids condensed on each tray are piped off.
Shorter chains condense in trays higher up because they have lower boiling points.
Thick residue at bottom called tar or bitumen can be used for road surfacing .
What are the conditions for cracking?
Heated to vapour
Passed over hot catalyst
What are conditions for thermal cracking?
High pressure
High temperature
What does thermal cracking produce?
Lots of alkenes
What are the conditions for catalytic cracking?
Slight pressure
High temperature
Presence of zeolite catalyst
What is catalytic cracking mainly used to produce?
Motor fuels
Aromatic hydrocarbons
What are the economics of cracking?
Demand of some fractions exceeds supply from crude oil distillation
Catalytic cheaper than thermal due to lower temperature and pressure
Thermal cracking can be used in all fractions including residue
What are the products of complete combustion?
Carbon dioxide and water
What are products of incomplete combustion?
Carbon monoxide and water
What can sulphur dioxide cause?
Acid rain which damages water sources, fish and plant life
What does particulates cause?
Cancer, exaggerate asthma
What do unburnt hydrocarbons cause?
Greenhouse gas, Photochemical smog
What does carbon monoxide cause?
Prevents O2 binding to haemoglobin, toxic
Describe flue gas desulphurisation.
CaCo3 thermally decomposes at high temperatures
At power station SO2 reacts with CaO at high temperatures
How do catalytic converters work?
Pollutants react with NO and this converts them into less harmful gasses.
