C8

Question 1

What are hydrocarbons

Answer 1

compounds that contain hydrogen and carbon only.

Question 2

What is crude oil

Answer 2

-a complex mixture of hydrocarbons
-containing molecules in which carbon atoms are in chains or rings
-an important source of useful substances(fuels and feedstock for the petrochemical industry)
-a finite resource.

Question 3

Process of separation of crude oil

Answer 3

-by fractional distillation
-heated crude oil enters near the bottom of a tall fractionating column which is hot at the bottom and gets cooler towards the top
-vapours from the oil rise through the column
-vapours condense when the temp of the column is cool enough
-liquids are led out of the column at different heights.
-some hydrocarbons with low bps leave the column as gas as do not condense
-ones with high bps leave the column as hot liquid bitumen.

Question 4

names and uses of different fractions

Answer 4

gases-fuel for domestic heating and cooking
petrol-fuel for cars
kerosene-fuel for aircrafts
diesel oil-fuel for some cars and trains
fuel oil-fuel for large ships and in some poweer stations
bitumen-used to surface roads and rooves

Question 5

How hydrocarbons in different fractions differ from each other

Answer 5

at top of column:
-smaller molecules
-low bp
-very volatile
-flows easily
-ignites easily
large molecules:
-high bp
-not very volatile
-not very viscous/dont flow easily
-does not ignite easily
-at bottom of column because column hotter at bottom.
-all mostly members of the alkane homologous series.

Question 6

What is a homologous series

Answer 6

-series of compounds which:
-have same general formula
-differe by CH(small 2) in molecular formulae from neighbouring compounds
-show a gradual variation in physical properties as exemplified by their bps
-have similar chemical properties.

Question 7

complete combustion of hydrocarbon fuels

Answer 7

CO2 and water are produced
energy is given out(exothermic)

Question 8

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

Answer 8

-happens when supply of oxygen is poor
-produces those because part of the carbon is not completely oxidised/ doesnt all react so produces carbon monoxide/soot.

Question 9

why is carbon monoxide a toxic gas

Answer 9

-absorbed by the lungs and binds with haemoglobin in red blood cells
-reduces capacity of blood to carry O2
-can cause drowsiness or death/ fall unconscious.

Question 10

soot

Answer 10

carbon released as fine black particles
-smoky flames and deposited as soot
-can cause breathing problems and blackens buildings
-blocks boilers/other appliances or cause fire.

Question 11

how impurities in hydrocarbon fuels result in sulfur dioxide

Answer 11

-many hydrocarbon fuels naturally contain sulfur impurities
-When fuels burnt, sulfur oxidises to form sulfur dioxide

Question 12

formation of acid rain and problems

Answer 12

-sulfur dioxide dissolves in water in clouds to form sulfourus acid
-O2 in air reacts with this to form sulfuric acid
-mixture from these two acids fall from clouds as acid rain
-damages natural and built environments
-reacts with metal and rocks(limestone) weakening and damaging buildings and statues
-damages plants and trees making them lose leaves and die
-makes rivers and lakes too acidic for some aquatic wildlife to survive

Question 13

oxides on N2

Answer 13

-when fuels are burnt at high temps, N2 and O2 from air react to produce oxides of N2
-atmospheric pollutants
-can react in sunlight to produce smog
-N2 dioxide is toxic
-can cause bronchitis and other lung conditions
-dissolves inj water in clouds creating acidic sol adding to acid rain

Question 14

advantages and dis of using hydrogen over petrol as fuel in cars

Answer 14

petrol is non-renewable and takes lots of energy to produce
hydrogen produced from natural gas or crude oil is also finite but nit with elevtrolysis of water
incomplete combustion happens with petrol as fuel producing carbon and carbon monoxide
water only product of combustion with H2
fewer H2 filling stations so ncould make it more hard to runn a car fuelled with H2
both very flammable
H2 releases more enrgy per kg than petrol
petrol liquid at room temo and H2 gas.

Question 15

kerosene, petrol, diesel oil and methane

Answer 15

k,p,do-non-renewable fossil fuel from crude oil
m-non-renew fossil from natural gas

Question 16

cracking

Answer 16

-breaking down of larger, saturated hydrocarbon molecules(alkanes) into smaller, more useful ones , some of which are unsaturated(alkene)
saturated=carbon atoms only joined by single bond
alkenes are more reactive than alkanes

Question 17

why is cracking necessary

Answer 17

-helps to macth supply of fractions with demand for them
-produces alkenes which are useful for npetrochemical industry
-frac dis produces too many big molecules and not enough small for demand so cracking accomidatesn the demand with a better supply

Question 18

what formed earths earlyb atmosphere

Answer 18

gases produced by volcanic activity

Question 19

earths early atmosphere contains

Answer 19

-little/no O2
-large amount of CO2
-water vapour
-small amounts of other gases
-

Question 20

why amount of CO2 decreased

Answer 20

Co2 dissolved as the oceans formed
growth of plants taking in CO2 and releasing O2 increased O2 by ps

Question 21

chemical test for O2

Answer 21

glowing splint at top of test tube with gas
re-ignites if gas is O2

Question 22

greenhouse effect

Answer 22

-CO2, methan and water vapour absorb heatv radiated nfrom earth=release energy keeping earth warm(greenhouse effect)

Question 23

uncertanties caused by location where climate change measurements were taken and historical accuracies

Answer 23

dont knoiw accurate histroy of bearth only estimate
measured in diff locations and earth was foermed diff back then

Question 24

todays atmosphere

Answer 24

-78 N2
21 O2
other =argon and co2
human effects from fossil fduels and livestock farming can be mitigated by consideer scale, risk and environmental implications