The production of silicon by the reaction of magnesium and sand is represented by the following chemical equation:
SiO2 + 2Mg → 2MgO + Si
The equation shows that 1 mole of silicon (Si) is produced from 2 moles of magnesium (Mg) and 1 mole of sand (SiO2).
The molar mass of silicon is 28.09 g/mol, so to produce 85 g of silicon, we need:
2/1 * 28.09 g/mol * (85 g / 28.09 g/mol) = 480 g of magnesium
To produce 85 g of silicon, we need 1/1 * 60.08 g/mol * (85 g / 28.09 g/mol) = 180 g of sand.