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Chemistry Igcse > C11 > Flashcards

C11 Flashcards

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1
Q

What are the chemical test for water?

A

(Anhydrous) Cobalt (II) chloride

(Anhydrous) copper (II) sulphate

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2
Q

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

A

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)

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3
Q

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

A

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)

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4
Q

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

A

> 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

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5
Q

Why is distilled water used in experiments?

A

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

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6
Q

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

A

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

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7
Q

What are some examples of water supplies?

A

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

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8
Q

How is water treated for impurities?

A

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

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9
Q

What is the composition of clean air?

A

78% nitrogen

21% oxygen

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

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10
Q

What are common pollutants in the air?

A

Carbon monoxide, sulphur dioxide, oxides of nitrogen

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11
Q

What are the adverse effects/sources of:
Carbon dioxide

A

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

Adverse effect:
Increase global warming -> climate change

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12
Q

What are the adverse effects/sources of:
Carbon monoxide

A

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

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13
Q

What are the adverse effects/sources of:
Carbon particulates

A

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

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14
Q

What are the adverse effects/sources of:
Methane

A

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

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15
Q

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

A

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

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16
Q

What are the adverse effects/sources of:
Sulphur dioxide

A

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)

17
Q

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

A

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

18
Q

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

A

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

19
Q

What conditions are needed for iron to rust?

A

Presence of oxygen and water

20
Q

How is carbon dioxide formed as a product of combustion?

A

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

21
Q

How is carbon dioxide formed as a product of respiration?

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

F A L S E :0

25
Q

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

A

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

26
Q

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

A

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

27
Q

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

A

> 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)

28
Q

What are the consequences of global warming?

A

> 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)

29
Q

What elements are needed in fertilizers and why?

A

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

30
Q

What water-soluble ions do fertiliser compounds usually contain?

A

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

31
Q

Describe the displacement of ammonia form its salts

A

> 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

32
Q

Explain the Haber process

A

> 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

33
Q

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

A

> 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

Chemistry Igcse (10 decks)

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