Please help with these post lab questions from \"Reduction of Benzophenone\". Po
ID: 1025664 • Letter: P
Question
Please help with these post lab questions from "Reduction of Benzophenone".
Post Lab Questions:
1) How does this parallel the hydrogenation of an alkene?
2) According to the balanced chemical equation, how many moles of ketone can be reduced in the presence of one mole of sodium borohydride?
3) Based on the amount of NaBH4 you used, how many moles of benzophenone could you reduce?
4) You should have found that sodium borohydride was used in excess relative to the amount required. About how many times more NaBH4 did you use in excess of the stoichiometric amount required to complete the reduction?
Procedure Outline 1. Place about 0.64 g of benzophenone and 4 mL of methanol in a 25 mL Erlenmeyer flask. 2. If necessary, warm the mixture to dissolve the benzophenone and then allow to cool back to room temperature. 3. To the benzophenone solution, add in one portion 0.64g of sodium borohydride. 4. Swirl the flask and allow the reaction mixture to stand at room temperature for 20 min. s. Add 2 ml of cold water and warm on a steambathlfor S minutes. 6. Cool the resulting mixture in an ice bath to precipitate a solid. 7. Collect the solid using vacuum filtration and air dry. 8. Determine the weight and melting point of the solid.Explanation / Answer
1. The hydrogenation of alkene follows the similar mechanism as that of reduction of ketone.
hydrogenation of alkene will yield alkane.
2. one mole of NaBH4 can reduce 4 moles of ketone according to balanced chemical equation.
3. mass of NaBH4 = 0.64 g
mol wt of NaBH4 = 37.83 g/mol
no of moles of NaBH4 = 0.64/37.83 = 0.0169 moles
0.169 moles of NaBH4 can reduce 0.0169 x 4 = 0.0676 moles of benzophenone.
4. wt of benzophenone = 0.64 g
mol wt of benzophenone = 182.217 g/mol
no of moles = 0.64/182.217 = 0.0035 moles
no of moles of NaBH4 required = 0.0035/4 = 0.00085 moles
NaBH4 actually taken = 0.0169 moles
excess = 0.0169/0.00085 = 19.88 times excess (exactly 19.26 imes)