alkanes

Question 1

general formula

Answer 1

CnH2n+2

Question 2

saturated

Answer 2

contain single carbon-carbon bonds only

Question 3

hydrocarbon

Answer 3

consisting of hydrogen and carbon only

Question 4

alkanes

Answer 4

saturated hydrocarbons

Question 5

fuels from crude oil

Answer 5

obtained from crude oil in order of fractional distillation, cracking and reformation of crude oil

Question 6

petroleum

Answer 6

mixture consisting mainly of alkane hydrocarbons

Question 7

petroleum fraction

Answer 7

mixture of hydrocarbons with a similar chain length and boiling point range

Question 8

fractional distillation

Answer 8

• crude oil is pre-heated and then passed into column
• the fractions condense at different heights
• the temperature of the column decreases upwards
• the separation depends on boiling point
• boiling point depends on size of molecules
• the larger the molecule the larger the london forces
• similar molecules (size, bp, mass) condense together
• and big molecules condense at the bottom at higher temperatures

Question 9

cracking

Answer 9

conversion of large hydrocarbons to smaller molecules by the breakage of C-C bonds

Question 10

economic reasons for cracking

Answer 10

• the petroleum fractions with shorter C chains (e.g. petrol and naphtha) are in more demand than larger fractions
• to make use of excess larger hydrocarbons and to supply demand for shorter ones
• product of cracking are more useful and valuable than the starting materials (e.g. ethane - poly(ethene) + ethane-1,2-diol + ethanol

Question 11

what does cracking involve

Answer 11

splitting of strong covalent bonds so requires high temperatures

Question 12

reforming

Answer 12

turns straight chain alkanes into branched and cyclic alkanes and aromatic hydrocarbons

Question 13

what is reforming for?

Answer 13

making motor fuels

Question 14

fuel

Answer 14

releases heat energy when burnt

Question 15

complete combustion

Answer 15

in excess oxygen, alkanes will burn with complete combustion

Question 16

products of complete combustion

Answer 16

CO2 + H2O

Question 17

incomplete combustion

Answer 17

if there is a limited amount of oxygen, incomplete combustion occurs
- produces less energy per mole than complete combustion

Question 18

products of incomplete combustion

Answer 18

CO (and/or C) +H2O

Question 19

what does carbon (soot)/particulates cause?

Answer 19

global dimming - reflection of the sun’s light + respiratory problems

Question 20

carbon monoxide

Answer 20

highly toxic but odourless gas. it can cause death if it builds up in an enclosed space due to faulty heating appliances.

Question 21

why is CO toxic to humans?

Answer 21

can cause a strong bond with haemoglobin in red blood cells. this is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin

Question 22

what impurities are found i petroleum fractions?

Answer 22

sulfur containing impurities which produce SO2 when they are burned
e.g. S + O2 = SO2

Question 23

why is SO2 bad?

Answer 23

SO2 is acidic and will dissolve in atmospheric water and can produce acid rain

Question 24

nitrogen oxides (NOX)

Answer 24

form from the reaction between N2 and O2 (N2 + O2 = 2NO) in the air reacts at the high temperatures and spark in the engine

Question 25

environmental consequence of nitrogen oxides

Answer 25

NO is toxic and can form smog
NO2 is toxic and acidic and forms acid rain

Question 26

environmental consequence of carbon dioxide

Answer 26

contributes towards global warming

Question 27

environmental consequence of unburned hydrocarbons

Answer 27

contributes towards formation of smog

Question 28

catalytic converters

Answer 28

these remove CO, NO(X) and unburned hydrocarbons (e.g. octane) from the exhaust gases, turning them into ‘harmless’ CO2, N2, H2O

e.g 2CO + 2NO = 2CO2 + N2
C8H18 + 25NO = 8CO2 + 12 1/2 N2 + 9H2O

Question 29

what are converters made out of?

Answer 29

ceramic honeycomb coated with a thin layer of catalyst metals platinum, palladium, rhodium - to give a large surface area

Question 30

is crude oil renewable or non renewable?

Answer 30

non- renewable resource - most fossil fuels come from crude oil which is non-renewable. fossil fuel reserves will eventually run out

Question 31

alternative renewable resources

Answer 31

biodiesel and alcohol (both made from plants)

Question 32

how are alcohols produced

Answer 32

fermentation of sugar from plants

Question 33

how is biodiesel produced

Answer 33

reacting vegetable oils with a mixture of alkali and methanol

Question 34

advantages of biofuels

Answer 34

• reduction of use of fossil fuels which are finite resources
• renewable
• biodiesal is more carbon-neutral
• allows fossil fuels to be used as a feedstock for organic compounds
• no risk of large scale pollution from exploitation of fossil fuels

Question 35

disadvantages of biofuels

Answer 35

• less food crops may be grown
• land not used to grow food crops
• rain forests have to be cut down to provide land
• shortage of fertile soils