environmental

• Air is a mixture of gases including:

  1. Nitrogen - 79%
  2. Oxygen - 20%
  3. Argon - 0.01%
  4. Carbon Dioxide - 0.03%
  5. H2O and other noble gases
• To prove that air contains CO2 and H2O:

  • anhydrous copper II sulphate will turn from white to blue in presence of water [H2O]
  • lime water [calcium hydroxide] will turn milky in presence of CO2
• To prove that air is 20% oxygen:

  • pass air through hot copper using 2 gas syringes until no change in volume occurs after apparatus is cooled
  • Observation -> volume of air in both syringes = 80cm^3 so 20cm^3 was absorbed by hot copper
  • Copper + Oxygen -> Copper II Oxide
• Copper II Oxide [ CuO ] is a black solid
• After test to prove there is 20% oxygen in air:

  • Major gas left is nitrogen
  • if a glowing splint approaches apparatus, it will extinguish due to no oxygen present
  • excess copper is used as it is an unreactive metal, it will oxidise on the surface to form black CuO, so it is used in excess so all oxygen is absorbed
  • Hot Mg/Al cannot be used as they are reactive enough to react with oxygen and nitrogen
• prepare Oxygen, Nitrogen and argon on a large scale [industrial preparation] by fractional distillation of liquid air
• Fractional Distillation Of Liquid Air

  • Air is liquid at -200
  • Nitrogen will separate first as it has the lowest boiling point
  • Water will separate as ice
  • CO2 will separate as dry ice
• Industrial Uses Of Oxygen:

  • in hospitals
  • for diving [oxygen tanks]
  • for manufacture of steel
  • reacts with acetylene gas to produce oxyacetylene flame which is used for welding and cutting metal
• Industrial Uses Of Nitrogen:

  • manufacture of ammonia
  • liquid nitrogen is used in supercooling as a food preservative
• Industrial Uses Of Carbon Dioxide:

  • fire extinguishers
  • fizzy drinks
• Industrial Uses Of Argon:

  • filling bulbs [unreactive]
  • in reactions which need inert atmosphere
• Processes that involve gases in air:

  • Respiration
  • Photosynthesis
  • Combustion
  • Corrosion of Metals
• Respiration and Photosynthesis maintain balance of oxygen and carbon dioxide percent in atmosphere
• photosynthesis -> plants absorb CO2 and H2O in presence of light and chlorophyll to give carbohydrates and release oxygen
• Chemical Equation For Photosynthesis -> 6CO2 + H2O -> C6H12O6 + 6O2
• Respiration -> oxygen is taken and CO2 is given
• Combustion:

  • burning of substances in presence of oxygen
  • an exothermic reaction
  • an oxidation reaction
• combustion equation - CH4 + O2 -> CO2 + H2O + heat energy
• fuels are substances that burn in oxygen giving large amounts of energy
• most fuels are hydrocarbons which when burned in excess oxygen give H2O, CO2 and energy
• if burning is done in poor supply of oxygen, incomplete combustion occurs and toxic gas carbon monoxide is given
• Metals -> burn in oxygen to give metal oxides. Most metal oxides are basic but some are amphoteric like ZnO and AL2O3
• Non-Metals -> burn in oxygen to give non metal oxides. Some non metal oxides are acidic while others may be neutral
• Na [Sodium] -> burns in oxygen with yellow flame and gives white solid [Na2O] which is basic and soluble
• Mg [Magnesium] -> burns in oxygen with bright white flame and gives white ash [powder] which is basic and slightly soluble
• Cu [Copper] -> forms an oxide without burning and gives black layer of CuO [copper II oxide] which is basic and insoluble
• Fe [iron] fillings -> burn in oxygen giving yellow sparks and gives black solid which is basic and insoluble
• C [Carbon] -> glows red hot when burned in oxygen and gives colorless gas [CO2] which is acidic in water [H2CO3]
• S [Sulfur] -> burns with a blue flame and gives colorless gas [SO2] which is acidic in water [H2SO4]
• P [Phosphorus] -> burns in oxygen with a yellow flame and gives white solid which is acidic in water [H3PO4]
• metal corrodes [tarnishes] when left in air as they react with oxygen and water in air
• Potassium, Sodium and Calcium corrode rapidly in air and rapidly oxidize therefore they are stored under oil
• Magnesium, Zinc and Aluminum form a protective oxide layer which prevents the metals from further oxidation
• Rust -> the reddish brown porous layer on the surface of iron or steel
• Conditions necessary for rust -> presence of oxygen and water
• Chemical name of Rust -> Hydrated Iron III Oxide
• Conditions encouraging rust -> presence of acid or salt which increase rate of rusting
• Painting, covering in layer of plastic and Electroplating are ways to prevent rust by preventing oxygen and water from reaching the iron
• Electroplating is when an object is coated with another metal using electricity
• Sacrificial Protection -> putting blocks of a more reactive metal like zinc or magnesium on iron because these metals have higher tendency to react with oxygen and water, they decrease rate of rusting