Organic 1: Alkanes

Question 1

what is an alkane

Answer 1

a saturated hydrocarbon

Question 2

what is the general formula of an alkane?

Answer 2

Cn H2n+2

Question 3

are the bonds in alkanes polar?

Answer 3

non-polar

carbon and hydrogen have similar electronegativities

Question 4

what intermolecular forces are in alkanes and why

Answer 4

only van der waals - bonds are non-polar

Question 5

are alkanes soluble in water

Answer 5

insoluble because hydrogen bonds in water are stronger than alkanes’ van der waals forces of attraction

Question 6

how reactive are alkanes

Answer 6

very unreactive

Question 7

which reactions will alkanes undergo

Answer 7

combustion and reaction with halogens

Question 8

what is crude oil? how is it formed? is it renewable? why?

Answer 8

• mixture of fractions (hydrocarbons with similar boiling points and properties)
• formed at high temperatures and pressures deep below earth’s surface over millions of years
• non renewable

Question 9

name the fractions from high to low boiling point

Answer 9

1. gases
2. gasoline/petrol/naphtha
3. kerosene/paraffin
4. diesel oil
5. lubricating oil/waxes
6. fuel oil
7. tar/bitumen

Question 10

what is fractional distillation and how does it work?

Answer 10

• crude oil is heated until mostly vaporised
• passed into a fractionating tower that is cooler at the tip than the bottom
• liquid fractions are piped off at the bottom
• vapours rise up the column and (via trays and bubble caps) condense when the temperature is lower than their boiling point
• shortest chain hydrocarbons condense at the top as they have the lowest boiling points

Question 11

what is fracking and how is it done?

Answer 11

• natural gas in shale rock
• drill into shale, force pressurised water and sand into rock to fracture it, collect gas
• HCl and methanol added to break up shale and prevent corrosion

Question 12

advantages and disadvantages of fracking?

Answer 12

advantages :
 - gas supply for many years 
 - reduces imported gas and electricity 
disadvantages :
 - lots of traffic to local area 
 - concern about amount of water used 
 - chemical additives can pollute water supplies 
 - can cause small earthquakes 
- combust CH4 --> CO2 
- global warming

Question 13

why are alkanes cracked?

Answer 13

to turn a long chain alkane, which is not very economically valuable, into a shorter chain alkane (more economically valuable because it can be used as a fuel) and an alkane (more reactive starting point for many products)

Question 14

what are the conditions for thermal cracking?

Answer 14

700-1200K temperature

UP to 7000 kPa pressure

Question 15

what is the intermediate for the reaction

Answer 15

free radicals

Question 16

what are the main products of thermal cracking

Answer 16

alkenes

Question 17

what are the conditions for catalytic cracking

Answer 17

lower temp - 720K
lower pressure but above atmospheric
zeolite catalyst (SiO2 and Al2O3) with a honeycomb structure to give a large surface area

Question 18

what are the main products of catalytic cracking

Answer 18

cycloalkanes
aromatic hydrocarbons
branched alkanes

Question 19

an equation for the combustion of propane

Answer 19

C3H8 + 5O2 –> 3CO2 + 4H2O

Question 20

what is a fuel

Answer 20

something which releases heat energy when combusted

Question 21

what are the five main fuels comprising of alkanes

Answer 21

methane
butane 
propane 
petrol (about C8) 
paraffin (C10 - C18)

Question 22

what is incomplete combustion and what products are formed in the case of alkanes

Answer 22

combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming

Question 23

which type of hydrocarbons are most likely to undergo incomplete combustion?

Answer 23

longer chains

Question 24

what is the environmental impact of carbon monoxide

Answer 24

toxic/poisonous

Question 25

what is the environmental impact of nitrogen oxides

Answer 25

form nitric acid - acid rain, photochemical smog

Question 26

what is the environmental impact of sulfur impurities/sulfur dioxide

Answer 26

form sulphuric acid --> acid rain

Question 27

what is the environmental impact of soot

Answer 27

asthma cancer global dimming

Question 28

what is the environmental impact of unburnt hydrocarbons

Answer 28

photochemical smog

Question 29

what is the environmental impact of carbon dioxide

Answer 29

greenhouse gas mean global warming increasing global temperatures speeds up climate change

Question 30

what is the environmental impact of water vapour

Answer 30

greenhouse gas - global warming | increases global temperatures therefore speeds up climate change

Question 31

what are flue gases

Answer 31

gases given out by power stations

Question 32

write two equations for two different ways of desulfurising flue gases

Answer 32

CaO(s)+2H2O(l)+SO2(g)+1/2O2(g)--> CaSO4.2H2O(s) or CaCO3(s)+SO2(g)+1/2O2(g)--> CaSO4+CO2(g)

Question 33

what are catalytic converters made up of

Answer 33

ceramic honeycomb coated with platinum, palladium and rhodium metals

Question 34

what do catalytic converters catalyse (include equations)

Answer 34

catalyse products from car exhausts 2CO(g) + 2NO(g) --> N2(g) + 2CO2(g) hydrocarbons+NO--> N2 + CO2 + H2O

Question 35

what are greenhouse gases

Answer 35

gases which trap infrared radiation, making the earth act like a greenhouse

Question 36

what is the greenhouse effect and how does it contribute to global warming

Answer 36

greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up --> global warming

Question 37

define carbon neutral activities

Answer 37

activities that produce no net carbon dioxide emissions

Question 38

how are halogenoalkanes formed from alkanes

Answer 38

free radical substitution reaction

Question 39

what are the three stages of free radical substitution?

Answer 39

1. initiation - breaking halogen bond to form free radicals 2. propagation - chain part of the reaction where products are formed but free radical remains 3. termination - free radicals removed, stable products formed

Question 40

what are the conditions needed for the formation of a free radical chlorine atom?

Answer 40

presence of UV light

Question 41

write equation for the reaction of CH4 with Cl2 to form CH3Cl

Answer 41

``` initiation - Cl2 --> 2Cl propagation Cl + CH4 -->HCl + CH3 CH3 + Cl2 --> CH3Cl + Cl termination CH3 + Cl --> CH3Cl 2Cl -->Cl2 CH3 + CH3 --> CH3CH3 ```

Question 42

what is the function of the ozone layer

Answer 42

protects the earth from harmful exposure to too many UV rays

Question 43

how do CFCs break the ozone layer down

Answer 43

free radical substitution

Question 44

write an equation for the overall decomposition of ozone into oxygen (o2)

Answer 44

2O3 --> 3O2

Question 45

write the free radical substitution equations to show how Cl free radicals catalyse the decomposition of O3

Answer 45

Cl2 --> 2Cl (in presence of UV light) Cl + O3 --> ClO + O2 ClO + O3 --> 2O2 + C overall: 2O3 --> 3O2