air and water

Question 1

Water is used in industry (4)

Answer 1

solvent
coolant
cleaning
chemical reactant (e.g. in the hydration of ethene)

Question 2

Water is used at home (3)

Answer 2

cooking
cleaning
drinking

Question 3

water purification (6-7)

Answer 3

screens - removes solid floating debris
aluminium sulfate - coagulate clay pieces = easier to remove
filtered through course sand - remove large insoluble debris
flocculants - chemical that makes particles sink to bottom
chlorine - kills bacteria + acidic
sodium hydroxide - neutralise water
sometimes add fluorine

Question 4

testing for water (2)

Answer 4

cobalt(II) chloride: blue –> pink (in water)

copper(II) sulfate: white –> blue (in water)

Question 5

composition of air (4)

Answer 5

nitrogen - 78%
oxygen - 21%
argon - 0.09%
carbon dioxide - 0.04%

Question 6

separating gases from air (5)

Answer 6

filter air - dust free
add KOH or NaOH - removes CO2
condensation or H2SO4 - removes water vapour
200atm & -200C = liquid air
fractional distillation - nitrogen / oxygen / noble gases

Question 7

air pollution - causes and effects (3)

Answer 7

> carbon monoxide: incomplete combustion
- breathing problems
- can kill if too much
sulfur dioxide: combustion of fossil fuels
- forms acid rain (kills organisms, corrodes stone/metal)
lead compounds: leaded petrol
- toxic = causes health issues

Question 8

sources of nitrogen oxide (2)

Answer 8

car engines

nitrogen & oxygen reacting under high pressures/temps

Question 9

effects of nitrogen oxide (3)

Answer 9

smog
breathing difficulties
acid rain

Question 10

denitrification

Answer 10

microbial process of reducing nitrate & nitrite = gaseous forms = nitrous oxide (N2O) and nitrogen (N2)

Question 11

catalyst converters

Answer 11

1st compartment: catalyse nitrogen oxides –> nitrogen
2nd compartment:
2NO → N2 + O2
2NO2 → N2 + 2O2
2CO + O2 → 2CO2
2NO + 2CO → N2 + 2CO2
2NO2 + 4CO → N2 + 4CO2
> CO2 produced = global warming but not toxic

Question 12

greenhouse gases & sources (3)

Answer 12

carbon dioxide - naturally present, fossil fuels & industry
methane - naturally present but less, organic matter & traps more heat
nitrous oxides - produced by soil bacteria, remains for long time

Question 13

explain greenhouse effect (6)

Answer 13

• sun rays enter atmosphere
• some absorbed by ground
• other reflected as longer wavelengths
• some emitted wavelengths –> atmoshpere –> space
• some trapped by greenhouse gases in atmosphere
• more heat trapped –> global warming

Question 14

results of climate change (7)

Answer 14

• water levels rise due to melting glaciers = flooding
• extinction of species due to habitat destruction
• more violent weather
• migration of species to more habitable areas
• spread of disease due to warmer climate
• loss of habitat
• less rainfall = desertification = less food production

Question 15

Sources of CO2 in the atmosphere (4)

Answer 15

• combustion of fossil fuels
• respiration
• decomposition of limestone
• reaction of acid with carbonates

Question 16

Removal of carbon dioxide from the atmosphere (2)

Answer 16

• photosynthesis

- dissolves in water = removed by shellfish = CaCO3 shells

Question 17

reactants for rust - hydrated iron(III) oxide (3)

Answer 17

• iron
• oxygen
• water
  (salt in water can be catalyst)

Question 18

stopping rust (4)

Answer 18

• paint
• plastic coating
• metal plating / galvanizing
• greasing / oiling

Question 19

Sacrificial Protection

Answer 19

zinc is more reactive than iron so it reacts with oxygen and water and corrodes instead of the iron, even if zinc is corroded its ions remain and react more readily than iron