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 Percent Yield Calculations

Percent yield calculations differ from limiting stoichiometry problems by only one extra step.

The question includes a mass recovered. Here is the formula you will use at the end of the problem.

When you read the question the mass of the product must not be used until the very end.

So.....put it in your pocket for later.

You are allowed to use moles, grams, liters in this equation, as long as actual and theoretical are both in these units.

EXAMPLE QUESTION #1 (Plain Stoichiometry not limiting)

2CO(g) + O2(g) --> 2CO2(g)

Calculate the % yield if 69.1g of CO combines with excess O2 to form an experimental yield of 48.3L of CO2 @STP.

See how it says yields 48.3L of CO2 save that for later (in your pocket).

Now determine the volume of of CO2 from 69.1g of CO using stoichiometry

Find the moles, the mol ratio, then find the volume of CO2

69.1g CO(1 mol CO/28.0g)= 2.57mol CO

2.57mol CO(2mol CO2/2mol CO)= 2.57mol CO2

2.57mol CO2(22.4L/1 mol)= 55.3L of CO2

Now take out that volume recovered and plug into the % yield equation.

(48.3L/55.3L) x 100%= 77.3% yield

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