Question

If you are reacting 4.00 g benzophenone (MM = 182.22 g/mol) and you want to add 1.5 equivalents of NaBH4 (MM = 37.83 g/mol), how much NaBH4 do you need to add to the reaction flask?

A) 0.55 g NaBH4

B) 6.00 g NaBH4

C) 1.25 g NaBH4

D) 1.75 g NaBH4

Answer 1

Given,

Mass of benzophenone = 4.00 g

Molar mass of benzophenone = 182.22 g/mol

The molar mass of NaBH₄ = 37.83 g/mol

Firstly calculating the number of moles of benzophenone from the given mass and molar mass,

= 4.00 g x ( 1 mol / 182.22 g)

= 0.02195 mol benzophenone

Now, we want to add 1.5 equivalents NaBH₄, thus multiplying to the number of moles of benzophenone by 1.5,

= 0.02195 mol x 1.5

= 0.03293 mol NaBH₄

Converting moles to grams,

= 0.03293 mol NaBH₄ x (37.83 g / 1 mol)

= 1.25 g NaBH₄

Thus, option C) 1.25 g NaBH₄ is the correct answer.