Final answer:
When calculating percentage yield, the choice between grams and moles does not matter as long as both actual and theoretical yields are in the same units. Percent yield can exceed 100% because of measurement errors or impurities, whereas yields close to 100% are ideal but rare in practice due to inefficiencies.
Step-by-step explanation:
Need for Consistent Units in Percentage Yield Calculation
When calculating percentage yield, it is not necessary to use a specific unit such as grams or moles; what is crucial is consistency in the units used for both actual and theoretical yields. This ensures that when you calculate the percentage yield by the formula (actual yield x 100%) / theoretical yield, the units cancel out, leaving you with a dimensionless percentage. In the context of chemistry labs, a percent yield greater than 100% suggests an error, likely due to impurities or incorrect measurements since the law of conservation of mass must be observed.
For practical applications, chemists and industries aim to obtain yields as close to 100% as possible to minimize waste and cost, yet often yields are less due to various inefficiencies. It is worth noting that in stoichiometric calculations and chemical reactions, conversion between grams and moles is commonly performed using molar mass, but regardless of whether the result is expressed in mass or moles, the formula for percent yield remains unchanged as long as both yields are in the same units.