Chem Chapter 15

• Rusting+ How to prevent it


  Forms on the surface of iron and requires both water and air. Can be prevented by coating iron in grease, paint, a less reactive metal or a more reactive metal. This can be applied through electroplating. Zinc is used to protect iron which makes the iron galvanised. Zinc has a stronger tendency to form positive ions and this is what occurs when it is oxidised. Protects iron from oxidation(sacrificial protection).
• Aluminium Alloys

  Very low density but when alloyed they are lighteweight and strong. Used on aircraft and armoured vehicles
• Gold alloys

  Usually alloyed with copper for jewellery

  Wears more easily by itself and can be allloyed to produce different shades

  24 carat is most pure and acts as a percentage e.g. 18 carats would be 3/4 pure
• Carbon Steels

  It is made when removing most of the carbon when obtaining iron from a blast furnace

  Cheap

  High Carbon Steel is strong but brittle

  Low Carbon Steel is soft and easily shaped

  Used in bodies of cars and machinery
• Alloy Steels

  Expensive

  Nickel steel alloys are used to make long span bridges and bike chains as they are resistant to stretching forces

  Tungsten steels operate under hot conditons

  Chromium nickel steels are used as stainless steels and are a combination of hardness, strength and resistance to corrosion so do not rust

  Good for cooking utensils
• Conditions for LD and HD Polymers

  For LD polymers high pressures and traces of oxygen cause ethene to form LD poly(ethene). The chains are randomly branched and not closely packed, reducing its density

  Using a catalyst at 50 degrees with a slightly raised pressure creates HD poly(ethene). They can pack more closely together and has a high softening temp
• Thermosoftening polymers and thermosetting polymers

  Thermosoftening polymers soften quite easily and reset when cooled and consist of individual polymer chains tangles up. Weak intermolecular forces

  Thermosetting do not melt when heated and have strong covalent bonds forming cross links between chains. Strong intermolecular forces and will char when heated
• Glass

  Made of sand, limestone and sodium carbonate making soda lime glass

  They are heated at 1500 and they melt to form molten glass and as it cools it forms a solid with the particles arranged randomly
• Ceramics

  Clay ceramics are hard but brittle and are electrical insulators

  Wet clay is molded and heated to 1000 degrees in a furnace

  Contain compounds of metals and non metals with ionic bonding between ions and covalent bonding between non metal atoms

  The atoms and ions arrange in giant structures that form layers

  When wet water molecules get between the layers but when heated the water is removed and strong bonds form between layers

  The higher the temp of the furnace the harder the ceramic
• Composites

  Made of two materials where one is surrounding and binding fragments or fibres of another to reinforce it

  Composites of ceramics with polymers are tough and flexible like fibre glass where glass threads are embedded into polymer resin making it low density

  Advanced composites like carbon fibres make it even more lightweight

  Concrete can be reinforced by setting around it steel rods to make it more resistant to bending
• Haber Process

  Since farmers take the entire plant nitrogen in the soil is not replaced through the natural cycle. Nitrogen in the air cannot be used as it is insoluble so to make it soluble in water the Haber process is used to firstly turn it into ammonia

  Raw starting materials are nitrogen and hydrogen which are purified, passed over an iron catalyst at a high temp and high pressure. The product of the reverse rxn is ammonia. It is removed by cooling the gases so the ammonia liquefies and can be separated.

  Remaining nitrogen and hydrogen are re-compressed and heated to be recycled
• Obtaining Nitrogen and Hydrogen for Haber process

  Nitrogen is separated from other gases in the air using fractional distillation of liquid air. The air needs to be cooled to be liquified which has high energy costs and high pressure pumps used to compress are expensive

  Hydrogen is made by reacting steam with methane at high temps which has energy costs as well as the price of methane
• How does higher pressure affect the yield of ammonia in the Haber process?

  It increases yield by shifting equilibrium right
• Why can't too much pressure be used in the Haber process?

  Pumps to compress air are expensive
• What is the optimal pressure for the Haber process?

  200 atmospheres
• Why is a relatively high temperature used in the Haber process despite the forward reaction being exothermic?

  To increase the rate of reaction
• What is the effect of temperature on the yield of ammonia in the Haber process?

  A low temperature would produce the highest yield
• What role does an iron catalyst play in the Haber process?

  It speeds up the reaction in both directions
• How does the use of a catalyst affect the yield of ammonia in the Haber process?

  It does not increase yield, only speed
• What is the main effect of using a catalyst in the Haber process?

  Produces ammonia more quickly
• What are the key factors affecting the Haber process?

  • Higher pressure increases yield
  • Optimal pressure is 200 atmospheres
  • Low temperature favors yield, but high temp increases rate
  • Iron catalyst speeds up both forward and reverse reactions
• Fertilisers in the Lab

  Compound salts of ammonia have many advantages as fertiliser

  Made in a neutralisation rxn between an acid and ammonia(an alakali)

  Phosphoric acid- ammonium phosphate

  Nitric acid- ammonium nitrate as 10% of ammonium in Haber process is converted to nitric acid which can form ammonium nitrate fertiliser

  Sulfuric acid- ammonium sulfate
• NPK Fertilisers in Industry

  Potassium, Nitrogen and Phosphorus are all needed for healthy growth but no compound containing all 3 have been made

  Therefore NPK fertiliser contains formulations of compounds to provide all 3

  Phosphorus are found in rock that is mined and needs to be treated with nitric or sulfuric acids to make fertiliser salts that are soluble

  Nitrogen compound is in ammonium nitrate from haber process

  Potassium comes from potassium salts mined from the ground like potassium chloride and potassium sulfate and these are soluble in soil unlike Phosphoric rocks
• Different ways Phosphate rock is treated

  Nitric acid- produces phosphoric acid and calcium nitrate. This is then neutralised with ammonia to make ammonium phosphate

  Sulfuric acid- makes a single superphosphate( a mixture of calcium phosphate and calcium sulfate)

  Phosporic acid to make triple superphosphate( calcium phosphate)
• Copper Alloys

  • Bronze is a mix of copper and tin
  • Used in ships propellers because of its toughness and resistance to corrosion
  • Brass is made by alloying copper and tin and is much harder than copper and is malleable so used for instruments
• Lab vs Industry Fertilisers

  Lab- dilute solutions of ammonia and nitric acid making it safe to work with. Ammonium nitrate can be produced in only a small amount at a time making it a batch process

  Industry- ammonia is used as a gas and nitric acid is concentrated making it much more dangerous as the rxn is exothermic as well. Ammonium nitrate can be produced thousands of kilos at a time making it continuous.