Please check my response thanks
2013 There is a compromise between maximising yield and minimising the environmental impact of industrial processes. Justify this statement with reference to the production of sulfuric acid. 7 marks
The production of sulfuric acid is achieved through the mining and contact process which involves the maximisation of yield with environmental considerations throughout the process.
Mining: Sulfur is extracted through Frasch process in which super-heated steam and high-pressure air is forced into an underground sulfur deposit, melting the Sulfur and forcing it to the surface where it solidifies. Although this process produces high purity sulfur, it causes land subsidence and requires the removal of trees for land, thus damaging natural ecosystems. Mining also requires energy which is obtained by burning of fossil fuels which releases CO2 thus contributing to global warming and enhanced greenhouse effect.
Contact process step 1: Sulfur obtained by Frasch process is heated in dry air in a combustion furnace, forming SO2
S(s) +O2(g) --> SO2(g) + heat. Heat produced via this exothermic reaction is used to generate steam to produce electricity thus minimising environmental impacts as it reduce the reliance on fossil fuels thus minimising the amount of CO2 released.
Contact process step 2: SO2 is passed through a catalytic converter and several beds of V2O5 catalyst where it is converted into SO3. 2SO2(g) + O2(g) -->2SO3(g) +heat. The conditions of the reaction are manipulated to maximise yield of SO3 with environmental considerations. The forward reaction is exothermic thus the increase in temperature will force the equilibrium to favour backward reaction in order to reduce some of the increased heat according to Le Chatelier’s principle (LCP) which would reduce the yield of SO3. If the temperature is too high, the catalyst will be damaged which makes it less efficient and if temperature is too low, the rate of reaction will decrease which leads to the decrease in yield of SO3. Thus, a compromise temperature of approx. 400 degrees is maintained to ensure temperature is low enough to encourage forward reaction and high enough for particles to have sufficient kinetic energy to undergo reaction. Heat released via the exothermic reaction is used to generate electricity and unreacted gases are recycled back into the converter to reduce the necessity to mine for sulfur thus minimising environmental impacts of enhanced greenhouse effect and land subsidence. High pressure will favour the forward reaction (LCP) in order to reduce some of the increase in pressure thus increasing yield of SO3. However, low pressure of 1-2atm is used instead as it will be dangerous and costly if it is too high. V2O5 catalyst lowers the activation energy which increases the rate of reaction and enables lower temperature to be used, thus lowering the energy requirement and cost, and moreover reducing the production of energy from burning of fossil fuels which releases CO2 which minimises environmental impact. The concentration of oxygen is maintained high to force equilibrium to the right (LCP) in order to reduce some of the increased concentration of Oxygen thus increasing yield of SO3.
Contact process step 3: SO3(g) is dissolved in concentrated H2SO4 to produce oleum: SO3(g) + H2SO4(l) -->H2S2O7(l). Water is then added to H2S2O7 to form concentrated H2SO4: H2S2O7(l) + H2O(l) -->2H2SO4(l).
Do I need to include catalyst even though it doesn’t increase the yield
and do i need to be more specific about the compromise temperature:
- Initial gas stream is at 1000 degrees after combustion of sulfur.
- Gas stream is cooled to about 550 degrees and passed over bed of V2O5 catalyst which produces 70% conversion of SO2 to SO3
- Gas stream is further cooled to 400 degrees and passed over a second catalytic bed, producing 97% conversion
- After conversion of SO3 to H2SO4 (via oleum), remaining gas stream is passed over final bed of V2O5 to produce 99.7% conversion
Assess the impact of atomic absorption spectroscopy (AAS) on the scientific understanding of the effects of trace elements 4 marks
Before AAS was developed there were no other techniques sensitive enough to measure low concentrations of trace elements. Therefore, scientists were not able to detect and determine concentration of trace elements. However, after the development of AAS, which measures intensity of certain wavelengths of light from the electromagnetic spectrum (different element absorb specific wavelengths of light), the concentration of trace element can be determined very accurately as low as 0.01 ppm. The lamp used in AAS emits specific wavelengths that corresponds to the element being measured thus absorption of element is not affected by presence of other elements. This allows scientist to measure concentration and rectify deficiency of specific trace element (eg. animal health could not be maintained due to Cobalt deficiencies in pasture in coastal SW Australia) by providing fertilisers or dietary supplements to animals to enhance plant growth and animal and human health. Thus, AAS has enabled scientists to detect and measure concentration of trace elements which led to the increase in scientific understanding of the effects of trace elements.