What is the Percent Yield?

Question

Percent Yield problem with 2 Step Stoichiometry (Non Mass-Mass)

Gold will dissolve in the acid mixture known as aqua regia according to the following:

Au + HNO₃ + 3HCl -> AuCl₃ + NO + 2H₂O

What is the Percent Yield from 197 grams Au if the reaction in lab actually produced 5.00 moles of water (H₂O)?

Answer 1

Hi Joshua A.,

Meaningless question. Yield is calculated for a particular product; the question does not in fact indicate the yield for water (though it implies it). Since gold mass ~ 197.0, your yield in terms of water would be 250% (5 vs. 2 predicted). But there is some great experimental difficulty in determining that "5.00 moles of water were produced", since the reaction is running in aqueous medium. How do you measure water in water, or how do you measure air in air? My guess is that this reaction was set up with an absorbant train to scrub H2O out from an exit stream of NO, and in reality excess water was evaporated and swept out with the NO, and not properly accounted for in the reaction vessel contents!

-- Cheers, --mr. d.