these 2 questions i need help with

Question

A chemist makes nitroglycerine, C3H5(NO3)3, from glycerol, C3H5(OH)3, and nitric acid according to the following balanced equation:

C3H5(OH)3 + 3HNO3 → C3H5(NO3)3 + 3H2O

a) In one experiment, 4.1 g of glycerol and 13.5 g of nitric acid produced 5.5 g of nitroglycerine. What was the percent yield of nitroglycerine? 

b) Offer a brief explanation as to why this reaction did not yield 100% products. 

Answer 1

C3H5(OH)3 + 3HNO3 → C3H5(NO3)3 + 3H2O   Balanced equation

a)  moles glycerol used = 4.1 g x 1 mol/92.09 g = 0.0445 moles

moles nitric acid used = 13.5 g x 1 mole/63.01 g = 0.214 moles

Which is the limiting reagent?  Mole ratio is 3 moles HNO3:1mole glycerol, thus glycerol is limiting.

Based on the limiting reagent, 0.0445 moles glycerol --> 0.0445 moles nitroglycerine

Theoretical mass of nitroglycerine = 0.0445 moles x 227 g/mole = 10.1 g nitroglycerine 

Actual yield = 5.5 g

% yield = 5.5 g/10.1g (x100%) = 54.5%

 

b)  Possible explanation for less than 100% yield is that the product (nitroglycerine) is volatile, and so some will become vapor.  Another possible reason is that perhaps the thermodynamics of the reaction (namely ∆G) is not favorable for the forward reaction even though the kinetics may be.  Finally, if the reaction is reversible, there is little likelihood that 100% production will be achieved.