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P 6 . 4 1 High - purity silicon, used in making electronic devices and solar cells, is produced from two inexpensive raw materials, sand

P6.41 High-purity silicon, used in making electronic devices and solar cells, is produced from two inexpensive raw materials, sand (SiO2) and coke (C). Typically, about 500kg sand and 200kg coke are placed in a retort. Sand and coke are then heated to about 400F, which produces solid silicon and carbon monoxide gas:
SiO2(s)+2C(s)Si(s)+2CO(g)
Si and CO are easily separated into solid and gas phases. Because of impurities in the sand, the solid Si phase is about 98.5wt% pure. This is not sufficiently pure, so two additional reactions are employed. First Si reacts with chlorine gas to make tetrachlorosilane:
Si(s)+2Cl2(g)SiCl4(g)
Tetrachlorosilane reacts with magnesium:
SiCl4(g)+2Mg(s)MgCl2(s)+Si(s)
MgCl2 is soluble in water (54.2g per 1000g water), whereas Si is not. Therefore, sufficient water is added to dissolve the MgCl2. Solid and liquid are separated by filtration. Si is recovered as a filtrate cake along with some entrained liquid (0.1lb liquid per lb solid). The cake is sent to a dryer to remove the entrained liquid.
Draw and label a flow diagram. Assuming 100% conversion of the Si-containing compounds in each of the reactions, calculate the quantities of all raw materials, the quantity of dried Si product, and the purity of the final product.
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