air and water Flashcards
Chemical Tests for Water
Cobalt (II) chloride turns blue to pink on the addition of water. This test is usually done using cobalt chloride paper.
The equation is:
CoCl2(s) + 6H2O(l) → CoCl2.6H2O(s)
Anhydrous copper (II) sulfate turns white to blue on the addition of water.
The equation is:
CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)
Water Treatment
Untreated water contains soluble and insoluble impurities.
Insoluble impurities include soil, pieces of plants and other organic matter.
Soluble impurities include dissolved calcium, metallic compounds and inorganic pollutants.
Filtration is the process used to remove large insoluble particles by passing the water through layers of sand and gravel filters that trap larger particles.
But bacteria and other microorganisms are too small to be trapped by the filters so chlorination is used.
This involves the careful addition of chlorine to the water supply which kills bacteria and other unwanted microorganisms.
Cholera and typhoid are examples of bacterial diseases which can arise by the consumption of untreated water.
Uses of Water
Water in industry
As a coolant to reduce the temperature of some industrial processes e.g: in nuclear power plants.
Watering crops.
As a solvent in many chemical production processes.
Hydroelectric power stations to generate electricity.
As a first raw material for many processes e.g: the production of ethanol from ethene and steam (water).
Uses of Water
Water in homes
Drinking, cooking and washing.
General sanitation.
In car radiators, for gardens and plants.
An Inadequate Supply of Water
Clean and safe water supply is very important to mankind.
Many problems arise in the event of an inadequate water supply, including:
Food shortages and famine due to a lack of crops which cannot grow without a clean water supply.
Poor sanitation leads to spread of bacteria and disease as drinking water becomes infected.
State the composition of clean, dry air as being
approximately 78% nitrogen, 21% oxygen and the remainder as being a mixture of noble gases and carbon dioxide
Uses of air
The gases available in the air have many important applications.
Oxygen is used in steel making, welding and in breathing apparatus.
Nitrogen is used in food packaging, the production of ammonia and in the production of silicon chips.
Both of these gases are separated from air by fractional distillation.
Fractional Distillation of Air
The air is first filtered to remove dust, and then cooled in stages until it reaches –200°C.
At this temperature the air is in the liquid state.
Water vapour and carbon dioxide freeze at higher temperatures and are removed using absorbent filters.
The Noble gases are still in the gaseous state at -200ºC, leaving a mixture of liquid nitrogen and oxygen.
The liquefied mixture is passed into the bottom of a fractionating column.
Note that the column is warmer at the bottom than it is at the top.
Oxygen liquefies at -183°C and nitrogen liquefies at -196°C.
Nitrogen has a lower boiling point than oxygen so it vaporises first and is collected as it rises in the gaseous state to the top of the column.
The liquid O2 is then removed from the bottom of the column.
Carbon monoxide
Sources: incomplete combustion of fossil fuels e.g: incomplete combustion of gasoline:
C8H18 + 9O2 → 5CO + 2CO2 + 9H2O
Adverse effects: poisonous, combining with hemoglobin in blood and prevents it from carrying oxygen.
Sulfur dioxide
Sources: combustion of fuels, natural gas and sulfide ores e.g: zinc blende (ZnS) in the extraction of zinc:
2ZnS + 3O2 → 2ZnO + 2SO2
Adverse effects: acid rain which causes corrosion to metal structures, buildings and statues made of carbonate rocks, damage to aquatic organisms. Pollutes crops and water supplies, irritates lungs, throats and eyes.
Oxides of nitrogen
Sources: reaction of nitrogen with oxygen in car engines and high temperature furnaces and as a product of bacterial action in soil.
Adverse effects: acid rain with similar effects as SO2 as well as producing photochemical smog and breathing difficulties, in particular for people suffering from asthma.
Compounds of lead
Sources: old water pipes, old paints, petrol in some kinds of racing cars and from very old engines.
Adverse effects: causes significant damage to the central nervous system, young infants are particularly susceptible to lead poisoning.
Complete and incomplete combustion of hydrocarbons produce different products.
Complete combustion occurs in … and produces …
Incomplete combustion occurs … and produces …
- excess oxygen
- CO2 and H2O
- oxygen deficient conditions
- CO, H2O and sometimes carbon.
Nitrogen oxides
These compounds (NO and NO2) are formed when nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces.
Exhaust gases also contain unburned hydrocarbons and carbon monoxide.
Cars are fitted with catalytic converters which form a part of their exhaust systems.
Their function is to render these exhaust gases harmless.
Catalytic converters
They contain a series of transition metal catalysts including platinum and rhodium.
The metal catalysts are in a honeycomb within the converter to increase the surface area available for reaction.
A series of redox reactions occurs which neutralises the pollutant gases.
Rusting of iron
Rusting is a chemical reaction between iron, water and oxygen that forms the compound iron (III) oxide.
Oxygen and water must be present for rust to occur.
Rusting is a redox process and it occurs faster in salty water since the presence of sodium chloride increases the electrical conductivity of the water.
Iron + Water + Oxygen → Hydrated Iron (III) Oxide
4Fe(s) + 3O2(g) + xH2O(l) → 2Fe2O3.xH2O(s)
Barrier Methods of Rust Prevention
Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen.
However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust.
Galvanising / Sacrificial Protection
Iron can be prevented from rusting using the reactivity series.
Galvanising is a process where the iron to be protected is coated with a layer of zinc.
ZnCO3 is formed when zinc reacts with oxygen and carbon dioxide in the air and protects the iron by the barrier method.
If the coating is damaged or scratched, the iron is still protected from rusting by the sacrificial method (magnesium can also be used).
This is because zinc is more reactive than iron and so it loses its electrons more readily:
Displacement of ammonia
Ammonia can be displaced from its salts by the addition of an alkali substance.
Farmers regularly add basic substances such as calcium hydroxide to their soil to neutralise any excess soil acidity.
If too much of the basic substance is added or if it has been added too soon after fertiliser has been added, then an ammonia displacement reaction may occur.
This involves the loss of nitrogen from the fertiliser, nullifying its effectiveness as a fertiliser.
For example, the salt ammonium chloride is used extensively in fertilisers and reacts with calcium hydroxide:
Manufacture of Ammonia
stages
Ammonia is manufactured using The Haber Process which occurs in five stages:
Stage 1: H2 and N2 are obtained from natural gas and the air respectively and are pumped into the compressor through pipes.
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 beads at a temperature of 450°C. Some of the hydrogen and nitrogen react to form ammonia:
Manufacture of Ammonia conditions
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.
However at a lower temperature the rate of reaction is very slow.
So 450ºC is a compromise temperature between having a lower yield of products but being made more quickly.
Pressure: 200 atm
A lower pressure would favour the reverse reaction as the system will try to increase the pressure by creating more molecules (4 molecules of gaseous reactants) so a higher yield of reactants will be made.
A higher pressure would favour the forward reaction as it will try to decrease the pressure by creating less molecules (2 molecules of gaseous products) 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 compromise pressure between a lower yield of products being made safely and economically.
The Greenhouse effect
explanatin and consequences
Caused by the increased concentration and effect of Greenhouse gases, mainly methane and carbon dioxide.
Explanation:
The Sun emits rays that enter the Earth’s Atmosphere
The heat is emitted back from the Earth’s surface
Some heat is reflected back out into Space
But some heat is absorbed by Greenhouse gases such as carbon dioxide and methane and is trapped within the Earth’s Atmosphere, causing the Earth’s average temperature to rise as a result
Consequences:
Climate change due to the increase in Earth’s temperature.
Water levels will rise as glaciers melt because of high temperatures, causing flooding in low-lying countries.
Extinction of species due to the destruction of natural habitats.
Migration of species as they will move to areas that are more habitable (no droughts).
Spread of diseases caused by warmer climate.
Loss of habitat due to climate change (animals that live on glaciers).
The Carbon Cycle
The carbon cycle describes the movement of carbon between the seas, land and atmosphere.
In the atmosphere, the main source of carbon is carbon dioxide.
Sources of CO2 in the atmosphere
Removal of carbon dioxide from the atmosphere
Photosynthesis: the process of producing glucose and oxygen from carbon and water in plants in the presence of chlorophyll and light:..
Carbon dioxide dissolves in the water in sea and oceans and is removed by shellfish for making their calcium carbonate shells.
Balancing the carbon
Carbon as carbonate, carbon dioxide or organic carbon compounds is present in the sea, the air and under the Earth.
There is a continuous cycle of these compounds between these sources called the carbon cycle.
There is a constant amount of carbon compounds in the sea, atmosphere and under the Earth.
As long as these are balanced, the amount of carbon dioxide in the atmosphere remains constant.
Scientists are worried that increasing the amounts of fossil fuels burned will increase global warming and unbalance the carbon cycle.
