Chemistry and the Environment

• chemical test for water

  using cobalt (II) chloride

  • usually done using cobalt chloride paper
  • turns blue to pink on the addition of water
  • equation: anhydrous cobalt (II) chloride + water --> hydrated cobalt (II) chloride
  • CoCl2 (s) + 6H2O --> CoCl2 . 6H2O (s)
  • keep in mind the reaction is a reversible reaction
• chemical test for water pt.2?

  using copper (II) sulfate:

  • anhydrous copper (II) sulfate turns white to blue on the addition of water
  • equation: anhydrous copper (II) sulfate + water --> hydrated copper (II) sulfate
  • CuSO4 (s) + 5H2O (l) --> CuSO4 . 5H2O (s)
  • remember both reactions are reversible
• testing for purity?

  pure substances melt and boil at specific and sharp temperatures

  • water has a b.p. of 100 °C and a m.p. of 0 °C
  • mixtures have a range of m.p. and b.p. as they consist of different substances that melt or boil at different temperatures
  • Impurities tend to increase the b.p. of water so impure water will boil at temperatures above 100 °C
  • impurities tend to decrease the m.p. of water, so impure will melt at temperatures below 0 °C
• distilled water

  water that has been heated to form a vapour, and then condensed back to a liquid

  • contains very few impurities
  • used in practical chemistry because of its high purity
  • tap water contains more impurities which could interfere with chemical reactions so is typically not used
• substances in water from natural sources

  water is found in natural sources such as lakes, rivers, and underground water sources (groundwater)

  • a rock that stores water = aquifer

  Water from natural sources may contain a variety of different substances, including:

  • dissolved oxygen
  • metal compounds
  • plastics
  • sewage
  • harmful microbes
  • nitrates from fertilisers
  • phosphates from fertilisers and detergents
• many substances enter water sources when rain falls and washes them into lakes, rivers or groundwater.

  • some are naturally occurring but many are a direct result of human activities

  depsite the term 'natural source,' water from these sources may contain lots of impurities and harmful substances and should not be confused with water which is clean and ready for use
• beneficial substances in Water

  • dissolved oxygen - essential for aquatic life
  • metal compounds - some provide essential minerals which are necessary for life (e.g. calcium and magnesium)
• potentially harmful substances in water?

  metal compounds - some are toxic like aluminium and lead

  • some plastics - harmful to aquatic life if many ways (e.g. getting trapped in plastic waste, dying of starvation as their stomach is filled with plastic)
  • sewage - contain harmful microbes which can cause disease
  • nitrate and phosphates from fertilisers - can promote growth of aquatic plant life which leads to deoxygenation of water. Ultimately this can cause damage to aquatic life in a process called eutrophication.
• what are soluble and insoluble impurities?

  insoluble impurities include:

  • soil
  • pieces of plants and other organic matter

  soluble impurities include:

  • dissolved calcium
  • metallic compounds
  • inorganic pollutants
• what is sedimentation?


  used for water treatment and when mud, sand and other particles will fall to the bottom of the tank due to gravity and form a layer of sediment
• what is filtration used for?

  used to remove smaller particles by passing the water through layers of sand and gravel filters that trap solid particles
• what is the function of carbon in water treatment

  carbon can be passed through carbon (in the form of charcoal) to remove tastes and odors
• what is chlorination?


  the careful addition of chlorine to the water supply which kills bacteria and other unwanted microorganisms since they are too small to be trapped by the filters.

  • Cholera and typhoid are examples of bacterial diseases which can arise from the consumption of untreated water
• What do fertilizers contain?

  NPK

  • 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 contain?

  ammonium ions (NH4+) and nitrate ions (NO3-) are sources of soluble nitrogen

  phosphate ions (PO4 3-) are a source of soluble phosphorus

  most common potassium compounds dissolve in water to produce potassium ions (K+)
• what does common fertiliser compounds include?

  ammonium...

  • nitrate = NH4NO3
  • phosphate = (NH4)3PO4

  potassium sulfate = K2SO4
• • ammonium salts and nitrates are commonly used as fertilisers
  • different fertilisers contain different amounts of fertiliser compounds, so each contains different proportions of nitrogen, potassium and phosphorus

  Look fo the compound of combination of compounds that contain the most elements from nitrogen, phosphorus and potassium.
• what are some uses of air?

  • Noble gases (e.g. Helium to fill balloons, argon for tungsten light bulbs, krypton for lasers in eye surgery)
  • Oxygen is used in steel making welding and breathing apparatus
  • Nitrogen is used in food packaging, the production of ammonia and in the production of silicon chips
  • oxygen and nitrogen are separated from the air by fractional distillation
• how can you investigate the percentage of oxygen in the air?

  by passing a known quantity of air over a metal.

  • The oxygen in the air will react with the metal, forming a metal oxide
  • the oxygen will be removed from the air and the volume of the air with the oxygen removed can be measured
• Method to investigate the percentage of O2 in the air

  1. Heat the copper using a Bunsen burner

  2. Push the plunger of the syringe containing air, forcing the air into the other plunger until all of the air has transferred

  3. Push the air back from the now filled plunger to the other plunger. Repeat this several times for about 3 minutes

  4. The copper will turn black as copper reacts with the oxygen in the air and copper oxide is produced

  5. Allow the apparatus to cool, ensuring all the gas is in one syringe and record the volume of gas
• The percentage of O2 in the air can be calculated from the results
• Carbon dioxide


  sources: complete combustion of carbon containing fuels such as fossil fuels (e.g. the complete combustion of methane: CH4 + 2O2 --> CO2 +2H2O)

  adverse effects: increases global warming, which leads to climate change
• carbon monoxide

  sources: incomplete combustion of carbon-containing fuels such as fossil fuels (e.g incomplete combustion of gasoline: C8H18 + 9O2 --> 5CO + 2CO2 + 9H2O)

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

  sources: incomplete combustion of carbon-containing fuels such as fossil fuels can also produce particulates of carbon (soot) (e.g. the incomplete combustion of methane can produce CO and C: 2CH4 + 3O2 --> 2CO + 4H2O and CH4 + O2 --> C + 2H2O)

  Adverse effects: respiratory problems and cancer
• 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 leading to climate change
• oxides 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.) It is also a product of bacterial action in the soil

  Adverse effects: produces photochemical smog, dissolves in rain to form 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 and causes respiratory problems
• sulfur dioxide

  sources: combustion of fossil fuels containing sulfur compounds. Power stations are a major source of sulfur dioxide

  adverse effects: dissolves in rain to form acid rain with similar effects as the acid rain caused by oxides of nitrogen
• remember...

  • complete combustion occurs in excess oxygen and produces CO2 and H2O.
  • Incomplete combustion occurs in oxygen-deficient conditions and produces CO, H2O and sometimes particulates of carbon (soot).
• Greenhouse effect

  The process where thermal energy from the Earth's surface is absorbed and re-emitted by greenhouse gases, trapping heat within the Earth's atmosphere and keeping the Earth warm
• Greenhouse effect

  1. Sun emits energy in the form of radiation that enters the Earth's atmosphere

  2. Some thermal energy is reflected from the Earth's surface

  3. Most thermal energy is absorbed and re-emitted back from the Earth's surface

  4. Energy passes through the atmosphere where some thermal energy passes straight through and is emitted into space

  5. Some thermal energy is absorbed by greenhouse gases (carbon dioxide and methane) and is re-emitted in all directions, reducing the thermal energy lost into space and trapping it within the Earth's atmosphere
• Greenhouse gases

  • Carbon dioxide
  • Methane
• consequences of global warming

  • limate 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 or in low-lying countries)
• how can CO2 emissions be reduced?

  by using hydrogen and renewable energy supplies such as solar or wind energy instead of burning fossil fuels

  • reducing the amount of livestock farming would decrease the methane emissions produced from digestion in animals
  • planting more trees would remove more carbon dioxide from the atmosphere
• how can the effects of acid rain be reduced?

  by decreasing the amount of oxides of nitrogen and sulfur dioxide that are produced

  • catalytic converters in vehicles can be used to remove oxides of nitrogen
• How can emissions of sulfur dioxide be reduced?

  by either

  • using fuels that contain low levels of sulfur
  • flue gas desulfurization - this involves reacting the sulfur dioxide emitted from burning fuels containing sulfur, with calcium oxide therefore removing it from the flue gas
• oxides of nitrogen


  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


  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 the reaction
• a series of redox reactions occurs which neutralises the pollutant gases

  • carbon monoxide is oxidized to carbon dioxide:
  • 2CO + O2 ---> 2CO2
  • oxides of nitrogen are reduced to N2 gas:
  • 2NO ---> N2 + O2
  • 2NO2 ---> N2 + 2O2

  A single reaction can summarise the reaction of nitrogen monoxide and carbon monoxide within a catalytic converter

  • 2NO + 2CO ---> N2 + 2CO2

  unburned hydrocarbons can also be oxidised to carbon dioxide and water

  • C8H18 + 12½O2 → 8CO2 + 9H2O
• photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts in green plants to make glucose