Chemistry 11: 03/04/12

percent Yield= The yield is the amount of product you obtain from a reaction. Suppose we own a factory that makes fertilizers or paint. We will want the highest yield possible, for the lowest cost.

The formula for percent yield is:

Example:

The medical drug aspirin is made from salicylic acid. 1 mole of salicylic acid gives 1 mole of aspirin. Given that the chemical formula for salicylic acid is C₇H₆O₃ and the chemical formula for aspirin is C₉H₈O₄.

In an experiment, 100.0 grams of salicylic acid gave 121.2 grams of aspirin. What was the percent yield?

Solution:

Step 1: Calculate the M_r (relative molecular mass) of the substances.

A_r : C = 12, H = 1, O = 16
So, M_r : salicylic acid = 138, aspirin = 180.

Step 2: Change the grams to moles for salicylic acid

138 g of salicylic acid = 1 mole
So, 100 g = 100 ÷ 138 mole = 0.725 moles

Step 3: Work out the calculated mass of the aspirin.

1 mole of salicylic acid gives 1 mole of aspirin
So, 0.725 moles gives 0.725 moles of aspirin
0.725 moles of aspirin = 0.725 × 180 g = 130.5 g
So, the calculated mass of the reaction is 130.5 g

Step 4: Calculate the percent yield.

The actual mass obtained is 121.2 g
So, the percent yield = 121.2 ÷ 130.5 × 100% = 92.9%

Percent purity= sometimes, the reactant we use is not pure, so before we can calculate how much product will form, we need to use percent purity to calculate how much reactant that actually is availablt to react.

The formula for percent yield is: