C11 Flashcards
What are the chemical test for water?
(Anhydrous) Cobalt (II) chloride
(Anhydrous) copper (II) sulphate
Describe the chemical test for water (including the equation):
Cobalt (II) chloride
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)
Describe the chemical test for water (including the equation):
Copper (II) sulphate
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)
How can you test for the purity of a substance (using water as an example) ?
> 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
Why is distilled water used in experiments?
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
What are some of the impurities that could be present in water?
2 types of impurities:
Soluble:
> calcium, metallic compounds, inorganic pollutants
Insoluble:
> soil plant matter, organic matter
What are some examples of water supplies?
Revivers, reservoirs, groundwater, aquifers (rocks that store water)
How is water treated for impurities?
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
What is the composition of clean air?
78% nitrogen
21% oxygen
1% other gases
> 0.9% argon
> 0.04% CO2
What are common pollutants in the air?
Carbon monoxide, sulphur dioxide, oxides of nitrogen
What are the adverse effects/sources of:
Carbon dioxide
Source:
Complete combustion of carbon-containing fuel
Ex: combustion of methane
CH4 + 2O2 -> CO2 + 2H2O
Adverse effect:
Increase global warming -> climate change
What are the adverse effects/sources of:
Carbon monoxide
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
What are the adverse effects/sources of:
Carbon particulates
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
What are the adverse effects/sources of:
Methane
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
What are the adverse effects/sources of:
Oxide of nitrogen
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
What are the adverse effects/sources of:
Sulphur dioxide
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)
What are some approaches to reducing emission of sulphuric dioxide and nitrogen?
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
How does a catalytic converter remove nitrogen monoxide (and unburned carbon monoxide/hydrocarbon) from exhaust emissions?
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
What conditions are needed for iron to rust?
Presence of oxygen and water
How is carbon dioxide formed as a product of combustion?
Most fuels contain carbon -> burn -> carbon dioxide:
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
methane + oxygen → carbon dioxide + water
How is carbon dioxide formed as a product of respiration?
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
How is carbon dioxide formed as a product of the reaction between an acid and a carbonate?
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
How is carbon dioxide produced as a product of thermal decomposition of calcium carbonate?
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
T or F: carbon dioxide and methane are not greenhouse gases
F A L S E :0
How has human activity contributed to the increase in this greenhouse gas:
Carbon dioxide
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
How has human activity contributed to the increase in this greenhouse gas:
Methane
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
Explain the process of heat getting trapped in the atmosphere through the greenhouse effect
> 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)
What are the consequences of global warming?
> 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)
What elements are needed in fertilizers and why?
Nitrogen: makes chlorophyll and protein and promotes healthy leaves
Potassium: promotes growth and healthy fruit and flowers
Phosphorus: promotes healthy roots
What water-soluble ions do fertiliser compounds usually contain?
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
Describe the displacement of ammonia form its salts
> 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
Explain the Haber process
> 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
Explain the the different aspects taken into account to balance the rate of reaction and yield in the Haber process
Economic
Temperature
Pressure
Catalyst
> 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