Module 2 Revision


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Module 2 Revision

  1. 1. Module 2 Revision Industrial Organic Chemistry
  2. 2. 2.5a. Conditions for ammonia and nitric acid manufacture <ul><li>The Haber process that turns nitrogen (from the air and hydrogen (from water or methane) into ammonia.  3H2(g) + N2(g) -> 2NH3(g) ∆ H=-92kJmol-1 </li></ul><ul><li>The optimum (best) conditions for this process which give the greatest yield are: </li></ul><ul><li>About 300 atmospheres; high pressure increases yield </li></ul><ul><li>about 450ºC ; high temperature cuts yield but increases rate </li></ul><ul><li>and the use of a catalyst, iron with KOH is used, to increase the rate </li></ul>
  3. 3. Making Nitric Acid Ammonia is changed into nitric acid in the Ostwald process.  This is another equilibrium process which starts with the reaction of ammonia and oxygen. 4NH 3 (g) + 5O 2 (g) -> 4NO(g) + 6H 2 O(g)  ∆ H= -900 kJmol-1 The optimum (best) conditions for this process which give the greatest yield are a pressure of 10 atmospheres a temperature of about 900 °C a catalyst of platinum and rhodium The nitrogen monoxide is then mixed with oxygen and flows up a column down which water flows.  The result is a solution of 65% nitric acid. 4NO(g) + 3O 2 (g) +2H 2 O(l) -> 4HNO 3 (aq)
  4. 4. 2.5b. Conditions for sulfuric acid manufacture <ul><li>Sulfuric acid is made in the Contact process.  This takes sulfur dioxide (made by burning sulfur) and reacts it in an equilibrium process with oxygen. </li></ul><ul><li>2SO 2 (g) + O 2 (g) -> 2SO 3 (g) ∆ H= -192kJmol-1 The optimum conditions for this process are: </li></ul><ul><li>a temperature of 430°C </li></ul><ul><li>a pressure of 2 atmospheres </li></ul><ul><li>a catalyst of vanadium pentoxide V 2 O 5 </li></ul>
  5. 5. 2.5e. The electrolytic extraction of aluminium <ul><li>Al is extracted from the ore bauxite, Al 2 O 3 .2H 2 O. The ore is purified by dissolving amphoteric Al 2 O 3   in hot aqueous sodium hydroxide under pressure.  Basic iron oxide not soluble.  Although silicon (IV) oxide is acidic it is not soluble due to strong bonds in giant structure. </li></ul><ul><li>Solid impurities are removed by filtration. Aluminium hydroxide is precipitated with  'seed' crystals and filtered. </li></ul><ul><li>Aluminium hydroxide is heated to produce aluminium oxide. </li></ul>
  6. 6. The Process <ul><li>Aluminium is manufactured by the electrolysis of pure aluminium oxide dissolved in molten cryolite (Na 3 AlF 6 ) to lower melting point from 2000º to 1000º, which saves money. </li></ul><ul><li>This mixture is heated and the molten liquid used as the electrolyte. Both electrodes are made of graphite (carbon).  The anode (+ve) is graphite and the cathode (-ve) is a graphite lining to a steel case. </li></ul>
  7. 7. Diagram .                                                                                                               
  8. 8. Cost of Aluminium Extraction <ul><li>The carbon anode is burned away by oxygen and has to be frequently replaced. 2O2-(l) -----> O2(g) + 2e- The cathode is steel Al3+(l) + 3e- -----> Al(l) </li></ul><ul><li>Aluminium is expensive despite being common because its manufacture requires large amounts of electricity.It is important because its low density, high strength, good electrical conductivity and resistance to corrosion make it valuable for aircraft manufacture, overhead power cables and many other uses. </li></ul>
  9. 9. 2.5g. The electrolysis of sodium chloride <ul><li>Sodium hydroxide, chlorine and hydrogen are produced from natural deposits of sodium chloride (rocksalt). This is the basis of the chloralkali industry. </li></ul><ul><li>Electrolysis of brine (salt solution) produces 1 tonne of chlorine at the same time as 1.13 tonnes of sodium hydroxide and 0.028 tonnes of hydrogen. </li></ul><ul><li>There are many different processes used in the electrolysis of brine. An aqueous solution contains the following ions: Na+, Cl-, H+ and OH-. </li></ul>
  10. 10. Diagram of a Membrane Cell Below is a diagram of a membrane cell:                                                                                                            
  11. 11. Reactions taking place <ul><li>The processes taking place at the electrodes are: </li></ul><ul><li>At Cathode 2H+(aq) + 2e- -----> H 2 (g) </li></ul><ul><li>At Anode 2Cl-(aq) -----> Cl 2 (g) + 2e- </li></ul><ul><li>In the solution in the cathode compartment the equilibrium </li></ul><ul><li>H2O(l) <=> H+(aq) + OH-(aq) </li></ul><ul><li>shifts to the right as H+ ion is converted to hydrogen gas. There is a build up of hydroxide ion and with the unaffected sodium ions remaining in the solution produces sodium hydroxide. </li></ul>
  12. 12. How the electrolysis works <ul><li>Saturated brine is pumped into the anode compartment. The brine level in the anode compartment is kept higher than the level in the cathode compartment so that brine seeps through the membrane, but hydroxide ion does not seep in the opposite direction. </li></ul><ul><li>The mixing of hydroxide ions and chlorine would produce unwanted sodium chlorate(I). The resulting solution leaving the cell, known as cell liquor, contains approximately 12% sodium hydroxide and 15% sodium chloride by mass. Evaporation and crystallisation leave a solution containing 50% sodium hydroxide and less than 1% sodium chloride. </li></ul><ul><li>If sodium chlorate (I) is required then the sodium hydroxide solution formed above is treated with gaseous chlorine to obtain sodium chlorate (I). </li></ul><ul><li>Cl2(g) + 2NaOH(aq) -----> NaCl(aq) + NaClO(aq) + H2O(l) </li></ul>
  13. 13. Uses of chlorine and sodium chlorate <ul><li>2.5h. Uses of chlorine and sodium chlorate (I) Chlorine: is used </li></ul><ul><li>as a cheap industrial oxidant in the manufacture of bromine because chlorine is a stronger oxidising agent than bromine </li></ul><ul><li>as a bleach because it oxidises coloured dyes to colourless compounds </li></ul><ul><li>as a germicide in the treatment of household water supplies and in swimming baths because it oxidises materials in the cell walls of bacteria hence killing them </li></ul><ul><li>to produce HCl in a reaction with hydrogen </li></ul><ul><li>to manufacture chlorinated hydrocarbon solvents </li></ul><ul><li>to manufacture chloroethene, a precursor for PVC. </li></ul><ul><li>Sodium chlorate (I): is used </li></ul><ul><li>as a bleach in laundries, as a disinfectant and in sewage treatment and as a germicide because it is a strong oxidising agent. </li></ul>