C11

Question 1

What are the chemical test for water?

Answer 1

(Anhydrous) Cobalt (II) chloride

(Anhydrous) copper (II) sulphate

Question 2

Describe the chemical test for water (including the equation):
Cobalt (II) chloride

Answer 2

Cobalt chloride turns from blue -> pink/purple when water is added

Usually done using cobalt chloride paper

Equation:
Anhydrous cobalt (II) chloride + water -> hydrated cobalt (II) chloride

CoCl2 (s) + 6H2O (l) -> CoCl2.6H2O (s)

Question 3

Describe the chemical test for water (including the equation):
Copper (II) sulphate

Answer 3

Anhydrous copper (II) sulphate turns from white to blue when water is added

Equation:
Anhydrous copper (II) sulphate + water -> hydrated copper (II) sulphate
CuSO4 (s) + 5H2O (l) -> CuSO4.5H2O (s)

Question 4

How can you test for the purity of a substance (using water as an example) ?

Answer 4

> pure substance melt/boil at specific+sharp temps
-> water bp -> 100°C and mp 0°C

> mixtures have a range of mp and bp -> they consist of different substances that each have different mp/bp

> mp and bp can therefore be used to test for purity
impurities -> usually increase bp and decrease mp

Question 5

Why is distilled water used in experiments?

Answer 5

Distilled water:
Water that has been heated into vapor then condensed back into a liquid -> very pure (why it is used in experiments)

Impurities (ex: tap water) can interfere with the chemical reactions -> not used

Question 6

What are some of the impurities that could be present in water?

Answer 6

2 types of impurities:
Soluble:
> calcium, metallic compounds, inorganic pollutants
Insoluble:
> soil plant matter, organic matter

Question 7

What are some examples of water supplies?

Answer 7

Revivers, reservoirs, groundwater, aquifers (rocks that store water)

Question 8

How is water treated for impurities?

Answer 8

SEDIMENTATION
> water pumped into sedimentation tanks for a few hours
-> mud, sand and other particles fall to bottom (gravity) and a layer of sediment is formed

FILTRATION
> filtration is used to remove smaller particles by passing water through layers of sand and gravel filters
> water can also be passed through carbon (charcoal) to remove taste and odors

CHLORINATION
> bacteria/microorganisms that are too small to be trapped by filters are killed by chlorine
> bacterial diseases such as cholera and typhoid from untreated water

Question 9

What is the composition of clean air?

Answer 9

78% nitrogen

21% oxygen

1% other gases
> 0.9% argon
> 0.04% CO2

Question 10

What are common pollutants in the air?

Answer 10

Carbon monoxide, sulphur dioxide, oxides of nitrogen

Question 11

What are the adverse effects/sources of:
Carbon dioxide

Answer 11

Source:
Complete combustion of carbon-containing fuel
Ex: combustion of methane
CH4 + 2O2 -> CO2 + 2H2O

Adverse effect:
Increase global warming -> climate change

Question 12

What are the adverse effects/sources of:
Carbon monoxide

Answer 12

Sources: incomplete combustion of carbon-containing fuels

ex: incomplete combustion of gasoline
C8H18 + 9O2 → 5CO + 2CO2 + 9H2O

Adverse effects: toxic, combining with haemoglobin in the blood and prevents it from carrying oxygen

Question 13

What are the adverse effects/sources of:
Carbon particulates

Answer 13

Sources: incomplete combustion of carbon-containing fuels -> produce particulates of carbon (soot)

e.g the incomplete combustion of methane can produce CO and C:
2CH4 + 3O2→ 2CO + 4H2O
CH4 + O2 → C + 2H2O

Adverse effects: respiratory problems and cancer

Question 14

What are the adverse effects/sources of:
Methane

Answer 14

Sources: waste gases from digestive processes of animals, decomposition of vegetation, bacterial action in swamps, rice paddy fields and landfill sites

Adverse effects: increases global warming, which leads to climate change

Question 15

What are the adverse effects/sources of:
Oxide of nitrogen

Answer 15

Sources: reaction of nitrogen with oxygen in the presence of high temperatures

e.g. in car engines, high-temperature furnaces and when lightning occurs, bacterial action in the soil

Adverse effects:
Produces photochemical smog
Dissolves in rain -> acid rain -> corrosion to structures (metal), statues (carbonate rocks), damage to aquatic organisms
Pollutes crops and water supplies
irritates lungs, throats and eyes and causes respiratory problems

Question 16

What are the adverse effects/sources of:
Sulphur dioxide

Answer 16

Sources: combustion of fossil fuels containing sulphur compounds.

Ex: Power stations

Adverse effects: dissolves in rain -> acid rain -> corrosion of structures (metal) and statues (carbonate rock)

Question 17

What are some approaches to reducing emission of sulphuric dioxide and nitrogen?

Answer 17

Catalytic converters in vehicles can be used to remove oxides of nitrogen

Emissions of sulphur can be reduced by:
> using fuel with lower levels of sulphur
> flue gas desulfurization -> involves reacting sulphur dioxide with calcium oxide -> removes it from the flue gas

BOTH HELP DEAL WITH ACID RAIN

Question 18

How does a catalytic converter remove nitrogen monoxide (and unburned carbon monoxide/hydrocarbon) from exhaust emissions?

Answer 18

CATALYTIC CONVERTERS
> contain transition metal catalyst (ex: platinum and rhodium)
-> in honeycomb inside converter -> increase surface area for reaction

> redox reaction -> neutralises the pollutant gas
Carbon monoxide is oxidised to carbon dioxide:
2CO + O2 → 2CO2

Oxides of nitrogen are reduced to N2 gas:
2NO → N2 + O2
2NO2 → N2 + 2O2

Summary of reaction of NO and CO in converter:
2NO + 2CO → N2 + 2CO2

Unburned hydrocarbons -> oxidised -> carbon dioxide and water:
C8H18 + 12½O2 → 8CO2 + 9H2O

Question 19

What conditions are needed for iron to rust?

Answer 19

Presence of oxygen and water

Question 20

How is carbon dioxide formed as a product of combustion?

Answer 20

Most fuels contain carbon -> burn -> carbon dioxide:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
methane + oxygen → carbon dioxide + water

Question 21

How is carbon dioxide formed as a product of respiration?

Answer 21

Respiration= process by which living beings gain energy from food Glucose (food) + oxygen (breathe) -> water and carbon dioxide:
C6H12O6 + 6O2 → 6CO2 + 6H2O
glucose + oxygen → carbon dioxide + water

Question 22

How is carbon dioxide formed as a product of the reaction between an acid and a carbonate?

Answer 22

when an acid reacts with a carbonate, carbon dioxide is produced:
MgCO3(s) + H2SO4(l) → MgSO4(aq) + CO2(g) +H2O(l)
magnesium carbonate + sulfuric acid → magnesium sulphate + carbon dioxide + water

Question 23

How is carbon dioxide produced as a product of thermal decomposition of calcium carbonate?

Answer 23

Thermal decomposition= breaking down of compounds into two or more products using heat
compounds has carbon + thermally decomposed -> carbon dioxide:
CaCO3(s) ——-heat——> CaO(s) + CO2(g)
calcium carbonate → calcium oxide + carbon dioxide
calcium carbonate = limestone

Question 24

T or F: carbon dioxide and methane are not greenhouse gases

Answer 24

F A L S E :0

Question 25

How has human activity contributed to the increase in this greenhouse gas: Carbon dioxide

Answer 25

Sources: combustion of wood and fossil fuels respiration of plants and animals thermal decomposition of carbonate rocks effect of acids on carbonates Main reason for increasing levels: combustion of fossil fuels increasing to meet our demands

Question 26

How has human activity contributed to the increase in this greenhouse gas: Methane

Answer 26

Sources: digestive processes of animals decomposition of vegetation bacterial action in swamps rice paddy fields landfill sites Main reasons for increasing levels: increase in animal farming Increased number of paddy fields and landfill sites

Question 27

Explain the process of heat getting trapped in the atmosphere through the greenhouse effect

Answer 27

> The Sun emits rays that enter the Earth’s atmosphere > The heat is absorbed and re-emitted back from the Earth’s surface > Some heat is reflected back out into space > some heat is absorbed by greenhouse gases-> trapped within the Earth’s atmosphere -> keeping the Earth warm > concentration of greenhouse gases increases (human activity) -> more heat is trapped > causes the Earth’s average temperature to rise (global warming)

Question 28

What are the consequences of global warming?

Answer 28

> Climate change <- due to increase in Earth’s temperature > Water levels rise <- glaciers melt (high temps) -> flooding > Extinction of species <- destruction of natural habitats > Migration of species to areas that are habitable (no droughts) > Spread of diseases caused by warmer climate > Loss of habitat due to climate change (animals that live on glaciers)

Question 29

What elements are needed in fertilizers and why?

Answer 29

Nitrogen: makes chlorophyll and protein and promotes healthy leaves Potassium: promotes growth and healthy fruit and flowers Phosphorus: promotes healthy roots

Question 30

What water-soluble ions do fertiliser compounds usually contain?

Answer 30

Ammonium ions (NH4 +) and nitrate ions (NO3 +) - sources of soluble nitrogen Phosphate ions (PO4 3-) - source of soluble phosphorus Most common potassium compounds dissolve in water to produce potassium ions (K +) Common fertilizers compound: Ammonium nitrate - NH4NO3 Ammonium phosphate - (NH4)3PO4 Potassium sulphate - K2SO4 Ammonium salts + nitrates -> very common > different fertilizers -> different ratios

Question 31

Describe the displacement of ammonia form its salts

Answer 31

> ammonia can be displaced from its salt by adding an alkali substance > farmers -> add basic substance (ex: calcium hydroxide) to soil to neutralize soil acidity > too much added -> ammonia displacement occurs -> loss of nitrogen from fertilizer (nulls effects) Ex: salt ammonium chloride is used extensively in fertilisers and reacts with calcium hydroxide: 2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O

Question 32

Explain the Haber process

Answer 32

> ammonia manufactured in exothermic reaction -> Haber process Stage 1: H2 and N2 obtained (from natural gas and air) -> pumped into compressor through pipe Stage 2: Gasses compressed -> about 200 atmospheres inside compressor Stage 3: Pressurized gases pumped into tank with layers of catalytic iron beds (temp: 450°C) some hydrogen and nitrogen react to from ammonia: N2 (g) + 3H2 (g) <-> 2NH3 Stage 4: unreacted N2 and H2 and ammonia passed into cooling tank -> ammonia liquified -> removed to a pressurized storage vessel Stage 5: Unreacted H2 and N2 recycled -> repeated

Question 33

Explain the the different aspects taken into account to balance the rate of reaction and yield in the Haber process Economic Temperature Pressure Catalyst

Answer 33

>if reaction reversible -> balance between rate of reaction and yield -> increased pressure + temp -> more ammonia ECONOMIC > needs to be profitable -> cost of extraction -> design of equipment -> manufacturing site -> production energy -> availability/cost of raw materials --> haber process: inexpensive for raw materials TEMPURATURE > higher temp —(endothermic) --> high yield of reactants > lower temp —(exothermic) --> higher yield of product -> BUT: lower temp -> lower rate of reaction > 450°C is the balance PRESSURE > lower pressure -> favor reverse reaction (more reactant) > system try to increase pressure -> higher yield > BUT: high pressure is dangerous+expensive > 200 atm is balance CATALYST > catalyst increase rate of reaction -> both forward and backward -> therefore helps reach equilibrium faster (position of equilibrium not changed -> just gets there faster) > allows more yield at lower temp (lowers activation energy) -> without: high temp -> expensive/less yield