Topic 8

Question 1

what are hydrocarbons

Answer 1

compounds containing carbon and hydrogen only

Question 2

describe crude oil

Answer 2

a complex mixture of hydrocarbons containing molecules in which carbon atoms are in chains or rings. its an important source of useful substances and a finite source .

Question 3

how is crude oil separated into simpler, more useful mixtures

Answer 3

crude oil separated by fractional distillation, oil is heated until most of it has turned into gas. gases enter a fractionating column. in column there’s a temperature gradient. longer hydrocarbons have higher boiling points, they turn back into liquids and drain out of column early on when near bottom. shorter hydrocarbons have lower boiling points, turn to liquid and drain out much later on, near to top of column where it cooler

Question 4

recall names and uses of different fractions

Answer 4

gases- domestic heating and cooking
petrol- fuel for cars
kerosene- fuel for aircraft
diesel oil- fuel for some cars and trains
fuel oil- fuel for large ships and some power stations
bitumen- surface roads and roofs

Question 5

describe shorter hydrocarbons

Answer 5

• easy to ignite
• lower boiling points
• tend to be gases at rt
• lower viscosity
• contain less carbon and hydrogen atoms

Question 6

what are 2 different homologous series of hydrocarbons

Answer 6

alkanes and alkenes

Question 7

describe long hydrocarbons

Answer 7

• usually liquids at rt
• higher boiling points
• harder to ignite
• higher viscosity
• contain more carbon and hydrogen atoms

Question 8

what is a homologous series

Answer 8

a series of compounds which; have same general formula, differ by CH2 in molecular formula from neighbouring compounds, show a gradual variation in physical properties and have similar chemical properties

Question 9

describe the complete combustion of hydrocarbon fuels

Answer 9

a reaction in which carbon dioxide and water are produced and energy is given out (exothermic)

Question 10

explain why the incomplete combustion of hydrocarbons can produce carbon and carbon monoxide

Answer 10

if there’s not enough oxygen around for complete combustion you get incomplete combustion. products contain less oxygen than carbon dioxide. as well as CO2 and H2O incomplete combustion produces CO and C

Question 11

explain how carbon monoxide behave as a toxic gas

Answer 11

carbon monoxide can combine with red blood cells and stop your blood from doing its proper job of carrying oxygen around body. lack of oxygen in blood supply to brain lead to fainting, coma, or death

Question 12

explain how impurities in some hydrocarbon fuels result in the production of sulfur dioxide

Answer 12

sulfur impurities in fossil fuels produces sulfur dioxide

Question 13

how is acid rain formed

Answer 13

sulfur dioxide mixes with clouds, it forms dilute sulfuric acid which falls as acid rain

Question 14

explain some problems associated with acid rain caused when sulfur dioxide dissolves in rain water

Answer 14

kills trees, damages limestone buildings and stone statues and can also make metal corrode

Question 15

evaluate advantages and disadvantages of using hydrogen, rather than petrol, as fuel in cars

Answer 15

a- very clean fuel
a- only waste product is water
a- hydrogen’s obtained from water which is renewable resource
d- need a special, expensive engine
d- hydrogen gas need to be manufactured which expensive and often uses energy from another source
d- hydrogen hard to store and not widely available

Question 16

what are petrol, kerosene, diesel oil and methane

Answer 16

petrol, kerosene, diesel oil are non-renewable fossil fuels obtained from crude oil. Methane is non-renewable fossil fuel found in gas

Question 17

what is cracking

Answer 17

cracking turns long saturated hydrocarbon (alkane) molecules into smaller unsaturated (alkene) and alkane molecules.

Question 18

describe cracking process

Answer 18

form of thermal decomposition, when one substance breaks down into at least two new ones when heat it. means breaking strong covalent bonds , so need lots of energy,so catalyst often used

Question 19

describe the problems caused by incomplete combustion producing carbon monoxide and soot in appliances that use carbon compounds as fuels

Answer 19

• during incomplete combustion tiny particles of carbon released into atmosphere. when fall back to ground, deposit themselves as black dust(soot)
• soot makes buildings look dirty, reduces air quality and can cause/ worsen respiratory problems

Question 20

explain production of nitrogen oxides and effects of them

Answer 20

• nitrogen oxides created from reaction between nitrogen and oxygen in air, caused by energy released by combustion reactions
• nitrogen oxides harmful pollutants contribute to acid rain, at ground level, can cause photochemical smog- type of air pollution that can cause breathing difficulties headaches and tiredness

Question 21

where did the earths early atmosphere come from

Answer 21

gases produced by volcanic activity formed Earth’s early atmosphere

Question 22

describe the Earth’s early atmosphere

Answer 22

• little or no oxygen
• large amounts of carbon dioxide
• water vapour
• small amounts of other gases

Question 23

explain how oceans were formed

Answer 23

water vapour in atmosphere condensed to form oceans

Question 24

how was the amount of carbon dioxide in the atmosphere decreased

Answer 24

• carbon dioxide dissolved into the oceans

- plants evolved and as photosynthesised CO2 removed and O2 produced

Question 25

describe chemical test for oxygen

Answer 25

-if gas will relight glowing splint

Question 26

explain how gases in atmosphere absorb heat radiated from the earth- the greenhouse effect

Answer 26

• earth radiates some of heat radiation it absorbs as longer wavelength, infrared (IR) radiation
• some IR radiation absorbed by greenhouse gases
• some IR radiation reflected back by greenhouse gases
• some IR radiation re-emitted back into space
• absorption and reflection of IR radiation by greenhouse gases keeps earth warm

Question 27

evaluate the correlation between the change in atmospheric carbon dioxide concentration, the consumption of fossil fuels and temperature change

Answer 27

• population increasing, more people respiring giving out more CO2, more people means more energy needed
• increased energy consumption comes mainly from burning fossil fuels, which releases CO2
• so as consumption of fossil fuels increase so do CO2 levels
• increase in CO2 enhances greenhouse effect meaning greater temperature increase

Question 28

evaluate the uncertainties caused by location where these measurements are taken and historical accuracy

Answer 28

-historical data less accurate, less data was taken over fewer locations and methods used to collect data were less accurate

Question 29

describe the composition of today’s atmosphere

Answer 29

nitrogen- 78%
oxygen- 21%
other including CO2- 0.037% and argon- 0.9%

Question 30

describe the effects on climate of increased levels of CO2 and methane generated by human activity

Answer 30

• methane produced by digestive processes of certain livestock, so more farming more methane produced
• CO2 produced by burning fossil fuels, so more enegy needed means more burning of fossil fuels so more CO2 produced

Question 31

describe that these effects on climate change may be mitigated

Answer 31

some scientists believe that current rises in global temp are just natural fluctuations and that we don’t have enough data to prove that global warming is caused by increasing CO2 emissions or human activity