stoichiometry! #2?

Question

in the commercial production of the element arsenic,
arsenic (III) oxide is heated with carbon, which reduces the oxide to the metal according to the following equation:

2As2O3 + 3C ----> 3CO2 + 4As

a) if 8.87g of As2)3 is used in the reaction and 5.33g of As are produced, what is the percent yield??

b)if 67g of carbon is used up in a different reaction and 425g of As are produced, calculate the percent yield of this reaction.

Answer 1

a) (Assuming C is not limiting)
Theoretical yield = 8.87 g As2O3 * 1 mole/197.8 g/mole * 4 moles As/2 moles As2O3 * 74.9 g As/mole = 6.72 g As

% yield = actual/theoretical * 100 = 5.33/6.72 * 100 = 79.3%

b)(Asuming As2O3 is not limiting)
Theoretical yield = 67 g C * 1 mole/ 12 g * 4 moles As/3 moles C * 74.9 g As/mole = 558 g As

% yield = actual/theoretical * 100 = 425/558 * 100 = 76.2%