Answer:
30%
Step-by-step explanation:
Percent yield uses the expression:
% Yield = (Actual mass)/(Theoretical mass)
We first need to determine what mass of NO we'd expect to get with 8.5 grams of NH3 in the following reaction:
4 NH₃ + 5 O2 ? 4 NO + 6 H₂O
Start with calculating the moles of NH3 that are contained in 8.5 grams of the compound by using the molar mass conversion factor:
(8.5 grams NH3)/(17.0 grams/mole) = 0.5 moles NH3
The balanced equation tells us that we would expect to obtain 4 moles of NO for every 4 moles of NH3. That's a 1:1 molar ratio. That means if we started with 0.5 moles, we'd expect to get the same number of moles of NO, 0.5 moles.
This assumes your lab partner is careful. An unexpected yield result can be attributed to many things: bad reactants, wrong temperature, short reaction time, sloppy partner, contamination, etc. DO NOT blame your partner since personal experience suggests a poor outcome.
So we should get 0.5 moles of NO (YES, that's hard to write) if everything went perfectly. 0.5 moles of NO is
(0.5 moles NO)*(30 g/mole) = 15 grams NO
We are told we recovered 4.5 grams of NO. That is a lot less than the 15 grams predicted (theoretical amount)
The percent yield is:
% Yield = (Actual grams NO)/(Theoretical grams NO)
% Yield = (4.5 g NO)/(15 grams NO)
% Yield = 30%