Air and water

Question 1

chemical tests for water using cobalt(II) chloride and copper(II) sulfate

Answer 1

● Cobalt(II)​ ​chloride:
○ Blue​ ​anhydrous​ ​cobalt(II)​ ​chloride​ ​turns​ ​pink​ ​in​ ​the​ ​presence​ ​of​ ​water
● Copper(II)​ ​sulfate:
○ White​ ​anhydrous​ ​copper(II)​ ​sulfate​ ​turns​ ​blue​ ​in​ ​the​ ​presence​ ​of​ ​water

Question 2

implications of an inadequate supply of water

Answer 2

safe water for drinking and water for irrigating crops

Question 3

the treatment of the water supply in terms of filtration and chlorination

Answer 3

o an​ ​appropriate​ ​source​ ​of​ ​fresh​ ​water​ ​is​ ​selected​ ​(rain​ ​provides​ ​water​ ​with low​ ​levels​ ​of​ ​dissolved​ ​substances​ ​and​ ​this​ ​collects​ ​in​ ​the ground/rivers/lakes)
o the​ ​water​ ​is​ ​passed​ ​through​ ​filter​ ​beds​ ​to​ ​remove​ ​different​ ​sized insoluble​ ​solids​ ​(filtration)
o the​ ​water​ ​is​ ​then​ ​sterilised,​ ​to​ ​kill​ ​microbes​ ​(sterilising​ ​agents​ ​include: ozone,​ ​UV​ ​light​ ​or​ ​chlorine)

Question 4

uses of water in industry and in the home

Answer 4

● In​ ​the​ ​home:​ ​drinking​ ​water,​ ​heating,​ ​plumbing

● In​ ​industry:​ ​water​ ​acts​ ​as​ ​a​ ​solvent,​ ​or​ ​a​ ​coolant

Question 5

Composition of clean, dry air

Answer 5

● 78% nitrogen
● 21% oxygen
● Rest is a mixture of noble gases and carbon dioxide

Question 6

the separation of oxygen and nitrogen from liquid air by fractional distillation

Answer 6

● Fractional distillation of liquid air separates oxygen and nitrogen
● oxygen has a boiling point higher than that of nitrogen
○ air is liquefied (around -200°C)
○ fractional distillation column temperature is increased until
nitrogen boils and rises to the top as a gas (around -196°C)
○ the nitrogen is collected and removed
○ the temperature is increased until oxygen boils and rises to the top as a gas (around -183°C) and oxygen is collected

Question 7

common pollutants in the air

Answer 7

● Carbon monoxide, sulfur dioxide, oxides of nitrogen and lead compounds

Question 8

source of each of these pollutants:

Answer 8

– carbon monoxide from the incomplete
combustion of carbon-containing substances
– sulfur dioxide from the combustion of fossil fuels which contain sulfur compounds (leading to ‘acid rain’)
– oxides of nitrogen from car engines
– lead compounds from leaded petrol

Question 9

the presence of oxides of nitrogen in car engines and their catalytic removal

Answer 9

● Oxides of nitrogen are formed from the heat and pressure found in a car engine
● Catalytic converters are used to remove oxides of nitrogen
○ Carbon monoxide + nitrogen monoxide -> nitrogen + carbon
dioxide
○ Nitrogen and carbon dioxide are relatively harmless gases
compared to carbon and nitrogen monoxides

Question 10

adverse effect of these common pollutants on buildings and on health and discuss why these pollutants are of global concern

Answer 10

● Carbon monoxide
○ Poisonous gas
■ Causes health problems – breathing difficulties, because it reduces the amount of oxygen that red blood cells can carry around the body
■ Too much carbon monoxide results in carbon monoxide poisoning, which can kill
● Sulfur dioxide
○ Forms acid rain
■ Kills plants and aquatic life
■ Erodes stonework
■ Corrodes metals
● Oxides of nitrogen
○ React with other pollutants, in sunlight, to form a photochemical smog, which causes breathing difficulties
○ Also forms acid rain
■ Kills plants and aquatic life
■ Erodes stonework
■ Corrodes metals
● Lead compounds
○ Lead is toxic
■ Causing health issues
● Petrol is used on a global scale, so these problems affect the whole world.

Question 11

conditions required for the rusting of iron

Answer 11

water and oxygen

Question 12

methods of rust prevention, specifically paint and other coatings to exclude oxygen

Answer 12

● To keep both oxygen and water away:
○ paint
○ cover in oil/grease
○ coat with plastic/another metal
● to keep oxygen away:
○ store in a vacuum container

Question 13

sacrificial protection in terms of the reactivity series of metals and galvanising as a method of rust prevention

Answer 13

● Galvanising: a less reactive metal can be coated with a more reactive metal to prevent it from rusting
● e.g. iron and steel can be coated with zinc
● This works because the more reactive metal is oxidised by oxygen in the air (i.e. rusts), protecting the less reactive metal underneath

Question 14

need for nitrogen-, phosphorus- and potassium-containing fertilisers

Answer 14

used​ ​as​ ​fertilisers​ ​to improve​ ​agricultural​ ​productivity
● plants​ ​need​ ​nitrogen,​ ​potassium​ ​and​ ​phosphorus​ ​in​ ​order​ ​to​ ​grow​ ​well,​ ​but​ ​can’t absorb​ ​it​ ​as​ ​a​ ​pure​ ​element-​ ​it​ ​must​ ​be​ ​a​ ​soluble​ ​salt​ ​(dissolved​ ​in​ ​water)​ ​that​ ​the roots​ ​can​ ​absorb
● nitrogen​ ​→​ ​nitrate​ ​and​ ​ammonium​ ​salts
● phosphorus​ ​→​ ​phosphate​ ​salts
● potassium​ ​→​ ​potassium​ ​salts

Question 15

the displacement of ammonia from its salts

Answer 15

● Ammonia​ ​can​ ​be​ ​produced​ ​by​ ​a​ ​displacement​ ​reaction​ ​involving​ ​ammonium​ ​salts
● If​ ​an​ ​ammonium​ ​salt​ ​is​ ​reacted​ ​with​ ​a​ ​strong​ ​base,​ ​ammonia​ ​will​ ​be​ ​produced
along​ ​with​ ​water​ ​and​ ​a​ ​salt ○E.g.​​NH4​C​l(aq)​​+​​NaOH(aq)​​->​​NH3​(​g)​​+​​H2​O​(l)​​+NaCl(aq)

Question 16

Describe and explain the essential conditions for the manufacture of ammonia by the Haber process including the sources of the hydrogen and nitrogen, i.e. hydrocarbons or steam and air

Answer 16

● The​ ​Haber​ ​Process​ ​is​ ​used​ ​to​ ​manufacture​ ​ammonia,​ ​which​ ​is​ ​used​ ​to​ ​produce nitrogen-based​ ​fertilisers
-Stage 1: H2 and N2, obtained from reacting methane with steam (H2) and found in the air (N2) are pumped into the compressor through pipe
-Stage 2: the gases are compressed to about 200 atmospheres inside the compressor
-Stage 3: the pressurised gases are pumped into a tank containing layers of catalytic iron beds at a temperature of 450°C. Some of the hydrogen and nitrogen react to form ammonia:
N2(g) + 3H2(g) ⇌ 2NH3(g)
-Stage 4: unreacted H2 and N2 and product ammonia pass into a cooling tank. The ammonia is liquefied and removed to pressurised storage vessels
-Stage 5: the unreacted H2 and N2 gases are recycled back into the system and start over again

Question 17

Conditions

Answer 17

Temperature: 450ºC

• A higher temperature would favour the reverse reaction as it is endothermic (takes in heat) so a higher yield of reactants would be made
• If a lower temperature is used it favours the forward reaction as it is exothermic (releases heat) so a higher yield of products will be made
• So 450ºC having a lower yield of products but being made more quickly

Pressure: 200 atm

• A lower pressure would favour the reverse reaction so a higher yield of reactants will be made
• A higher pressure would favour the forward reaction so a higher yield of products will be made
• However high pressures can be dangerous and very expensive equipment is needed
• So 200 atm is a lower yield of products being made safely and economically

Question 18

carbon dioxide and methane are greenhouse gases

Answer 18

Lead to Green house gas effect.
● There​ ​are​ ​several​ ​potential​ ​effects​ ​of​ ​global​ ​climate​ ​change
o Extinction​ ​of​ ​species
o Raising​ ​sea​ ​levels​ ​due​ ​to​ ​the​ ​melting​ ​of​ ​polar​ ​ice​ ​caps
o Increased​ ​risk​ ​of​ ​skin​ ​cancer​ ​due​ ​to​ ​more​ ​dangerous​ ​UV​ ​rays​ ​hitting​ ​the surface​ ​of​ ​the​ ​Earth

Question 19

formation of carbon dioxide:

Answer 19

● The​ ​complete​ ​combustion​ ​of​ ​carbon-containing​ ​substances
● Respiration
● The​ ​reaction​ ​between​ ​an​ ​acid​ ​and​ ​a​ ​carbonate
● The​ ​thermal​ ​decomposition​ ​of​ ​a​ ​carbonate

Question 20

carbon cycle

Answer 20

o CO2​ ​​ ​is​ ​emitted​ ​from​ ​respiration​ ​and​ ​combustion
o CO2​ ​​ ​is​ ​absorbed​ ​to​ ​make​ ​carbohydrates​ ​in​ ​photosynthesis
o Animals​ ​eat​ ​these​ ​plants​ ​and​ ​the​ ​carbon​ ​consumed​ ​is​ ​released​ ​as​ ​CO2​ formed​ ​during​ ​respiration
o These​ ​animals​ ​and​ ​plants​ ​eventually​ ​die​ ​and​ ​decomposers​ ​feed​ ​on​ ​these dead​ ​organisms,​ ​the​ ​carbon​ ​is​ ​returned​ ​to​ ​the​ ​atmosphere​ ​as​ ​CO2​

Question 21

sources of methane

Answer 21

● Production​ ​and​ ​use​ ​of​ ​fossil​ ​fuels
● Livestock​ ​farming
● Decomposition​ ​of​ ​vegetation