Ch. 3 - Sulfuric Acid Flashcards
Process used to extract sulfur from mineral deposits
Frasch Process
Three uses of sulfuric acid in industry
1) Sulfuric acid combined with ammonia NH3 can be used to produce fertilisers such as superphosphate and ammonium sulfate
2) Can be used for pickling of iron or steel to remove surface rust (Fe2O3) before galvanising, coating with tin, or applying powder to coatings
3) Can be used as a catalyst during the formation of ethanol from ethylene
- C2H4 (g) + H2O (g) –diluteH2SO4–> C2H5OH (l)
4) Used as an electrolyte in car lead acid batteries
- overall: Pb (s) + PbO2 (s) + 2 H2SO4 (aq) —> 2 PbSO4 (aq) + H2O (l)
Describe Frasch process
- Three concentric pipes are placed into the deposit
- Superheated and pressurised water at around 160*C is injected into the sulfur deposit through the outermost pipe
- This melts the sulfur (mp 113) to form an emulsion, and increases the pressure in the chamber
- Compressed air is injected through the innermost pipe, forcing the emulsion to the surface up through the middle pipe due to its low density
- When the mixture cools, solid sulfur separates from the water and 99.5% pure sulfur is obtained
Identify the properties of sulfur which allow for its extraction
1) Low MP - caused by weak dispersion forces, allows superheated pressurised water to readily melt it
2) Low density - ensures that the compressed air can lift the sulfur-water emulsion up to the surface
3) Insoluble in water and unreactive - the sulfur can be simply recovered after the emulsion cools
4) Non-toxic and non-volatile nature - health of miner aren’t compromised
Analyse potential environmental issues associated with sulfur extraction
Though sulfur is odourless and non-toxic, its extraction still involves environmental issues.
- The hot water used in the process may cause thermal pollution and may contain some dissolved minerals - hence should be recycled to avoid disrupting local ecosystems
- Once the sulfur is extracted, the remaining caverns can lead to earth subsidence - difficult to back-fill and gradually become filled with groundwater
- If sulfur produced is not cooled quickly, it is easily oxidised to toxic SO2 or reduced to H2S, both of which are serious air pollutants
Name process for production of H2SO4 from its raw materials
The Contact process is used to produce sulfuric acid from elemental sulfur, and is divided into 3 steps
Identify the steps (formations) involved in the contact process and give equations.
1) The formation of sulfur dioxide SO2
- S(l) + O2 (g) –> SO2 (g)
2) The formation of sulfur trioxide SO3
3) The formation of sulfuric acid H2SO4
- H2S2O7 (l) + H2O (l) —> 2 H2SO4 (l)
Second step of contact process
Second step is the formation of sulphur trioxide
- The sulfur dioxide is mixed with air at a pressure of slightly above 1 atm.
- It is passed into a converter with 3 or 4 beds of vanadium(V) oxide catalyst at 400 - 550oC, where it is oxidised to produce sulfur trioxide
- SO2 (g) + 1⁄2O2 (g) SO3 (g)
∆H = -99 kJ mol-1
Third step of contact process
The third step is the formation of sulfuric acid
- The cooled sulfur trioxide is dissolved in sulfuric acid to produce oleum
- SO3 (g) + H2SO4 (l) -> H2S2O7 (l) - Water is mixed with oleum to produce 98% sulfuric acid
- H2S2O7 (l) + H2O (l) -> 2H2SO4 (l)
Outline the steps and conditions necessary for the Contact process
1) The formation of sulfur dioxide SO2
• Elemental sulfur is melted and sprayed under pressure into an excess of dry air (with oxygen) in the combustion chamber. Alternatively, sulfur is roasted in a smelter.
- S(l) + O2 (g) –> SO2 (g)
2) The formation of sulfur trioxide SO3
• The sulfur dioxide is mixed with air at a pressure of slightly above 1 atm
• It is passed into a converter with 3 or 4 beds of vanadium(V) oxide catalyst at 400 - 550oC, where it is
oxidised to produce sulfur trioxide
3) The formation of sulfuric acid H2SO4
• The cooled sulfur trioxide is dissolved in sulfuric acid to produce oleum
• Water is mixed with oleum to produce 98% sulfuric acid
- H2S2O7 (l) + H2O (l) —> 2 H2SO4 (l)
First step of contact process
The first step is the formation of sulfur dioxide
- Elemental sulfur is melted and sprayed under pressure into an excess of dry air (with oxygen) in the combustion chamber. Alternatively, sulfur is roasted in a smelter.
- S(l) + O2 (g) -> SO2 (g)
Describe the reaction conditions necessary for the production of SO2 and SO3
Production of SO2
• S(l) + O2 (g) —> SO2 (g)
• High temperature is required for combustion
• The elemental sulfur is sprayed to increase the surface area of the reactant and promote the reaction
• Dry air is required to avoid acid mist and corrosion in pipes
• Excess of oxygen in dry air is necessary to ensure complete combustion and to maximise yield
Production of SO3
• SO2 (g) + 1⁄2 O2 (g) SO3 (g)
∆H = -99 kJ mol-1
• The sulfur dioxide mixed with air passes over the catalyst beds at varying temperatures between 400
and 550oC
• The pressure is slightly above 1 atm, since the small increases in yield allowed by higher pressures are
not worth the cost and danger of high pressure equipment
• A small excess of oxygen is used
• Yield is favoured by high pressure, low temperature and excess of oxygen
• Rate of reaction is favoured by high pressure, high temperature and the presence of a catalyst
• Hence compromise temperature conditions between high yield and high rate are required
Conditions required for the production of SO2
Production of SO2
• S(l) + O2 (g) —> SO2 (g)
• Excess oxygen is required to maximise yield and to avoid unwanted products resulting from incomplete combustion
Conditions required for the production if SO3
SO2 (g) + 1⁄2 O2 (g) -> SO3 (g)
∆H = -99 kJ mol-1
- Yield (due to equilibrium conditions) is favoured by high pressure, low temperature and excess of oxygen
- Rate of reaction is favoured by high pressure, high temperature and the presence of a catalyst
- Hence compromise temperature conditions between high yield and high rate are required
- The pressure is slightly above 1 atm, since the small increases in yield allowed by higher pressures are not worth the cost and danger of high pressure equipment
Apply relationship b/w rates of reaction and equilibrium conditions to the production of SO2 & SO3
Production of SO2
• S(l) + O2 (g) —> SO2 (g)
• Excess oxygen is required to maximise yield and to avoid unwanted products resulting from incomplete combustion
Production of SO
• SO2 (g) + 1⁄2 O2 (g) SO3 (g)
∆H = -99 kJ mol-1
• Yield (due to equilibrium conditions) is favoured by high pressure, low temperature and excess of oxygen
• Rate of reaction is favoured by high pressure, high temperature and the presence of a catalyst
• Hence compromise temperature conditions between high yield and high rate are required
• The pressure is slightly above 1 atm, since the small increases in yield allowed by higher pressures are
not worth the cost and danger of high pressure equipment
