Manufacturing Chemicals Flashcards
What materials are needed for making ammonia?
Nitrogen from the air
Hydrogen from natural gas
describe the manufacture of ammonia by the Haber process, including the essential conditions
Haber process takes nitrogen from the air and hydrogen from natural gas and combines them to make ammonia. It uses 1 volume of nitrogen to 3 volumes of hydrogen because an excess of either would clutter the reaction vessels with molecules that wouldn’t have anything to react with. The process is done at 450 degrees because it is a compromise temperature, producing a reasonable yield of ammonia reasonably quickly. If it was low, the reaction would take a long time to produce any ammonia.
The pressure is at 200atm because it is a compromise, a higher pressure would cost more to generate than you would get back in value. Iron is used as a catalyst to speed up the reaction, if there was no catalyst it would be so slow that virtually no ammonia would be produced.
How are the unreacted gases recycled?
Each time the gases pass through the reaction vessel, only 15% of the gases combine to make ammonia. The reaction mixture is cooled, and the ammonia condenses as a liquid. The unreacted gases can simply be recycled through the reactor
describe the use of ammonia in the manufacture of nitric acid and fertilisers
Put into fertilisers; contains nitrate ions, which plants need to make amino acids
Reacts with oxygen to make nitric acid
the raw materials used in the manufacture of sulfuric acid
Sulfur and Oxygen
describe the manufacture of sulfuric acid by the contact process
Burn sulfur in the air to make sulfur dioxide. The sulfur dioxide is converted into sulfur trioxide using an excess of air from the previous processes. An excess is used to make sure as much sulfur dioxide is converted to sulfur trioxide.
Because the forward reaction is exothermic, there would be a higher percentage conversion at a low temperature so 450 is a compromise. At 2atm the conversion is so good that it isn’t economically worthwhile to use higher ones. The catalyst, Vanadium oxide has no effect on the percentage conversion but helps to speed up the reaction.
The sulfur trioxide is absorbed in concentrated sulphuric acid to give oleum. This is converted into twice as much concentrated acid by careful addition of water.
describe the use of sulfuric acid in the manufacture of detergents, fertilisers and paints
Sulfuric acid is used to extract the white pigment, titanium dioxide from titanium ores in the manufacture of paint.
describe the manufacture of sodium hydroxide and chlorine by the electrolysis of concentrated sodium chloride solution
Very hot water under pressure is pumped down into salt deposits. The salt dissolves and the solution is pumped back to the surface. The solution is electrolysed in a diaphragm cell. At the anode, chloride ions are discharged to produce chlorine gas. At the cathode, hydrogen ions from water are discharged to produce hydrogen gas.
More and more water keeps splitting up to replace hydrogen ions as soon as they are discharged. Each time the water splits up it produces a hydroxide ion as well. That means there will be a build up of sodium and hydroxide ions on the right-hand compartment - NAOH if formed. NAOH solution is concentrated by evaporating it. Most of the NACL crystallises out as solid salt. This can be separated, redissolved and recycled again.
write ionic half-equations for the reactions at the electrodes
Anode: 2Cl- —> Cl2 + 2e-
Cathode: 2H+ + 2e- —> H2
