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To determine the amount of sodium borohydride (NaBH4) needed to reduce 75 mg of benzil, we need to consider the stoichiometry of the reaction. Here's a breakdown:
1. Balanced Chemical Equation:
Benzil (C14H10O2) + 2 NaBH4 → 1,2-Diphenylethane-1,2-diol (C14H14O2) + 2 NaBO2 + 4 H2
2. Molar Masses:
Benzil: 210.23 g/mol
NaBH4: 37.83 g/mol
3. Stoichiometry: The equation shows that 2 moles of NaBH4 are required to reduce 1 mole of benzil.
4. Calculations:
Convert 75 mg of benzil to grams: 75 mg / 1000 mg/g = 0.075 g
Calculate moles of benzil: 0.075 g / 210.23 g/mol = 3.57 x 10^-4 mol
Moles of NaBH4 needed: 3.57 x 10^-4 mol benzil
(2 mol NaBH4 / 1 mol benzil) = 7.14 x 10^-4 mol NaBH4
Mass of NaBH4 needed: 7.14 x 10^-4 mol
37.83 g/mol = 0.027 g = 27 mg
Therefore, approximately 27 mg of sodium borohydride is needed to reduce 75 mg of benzil.