April 4 2011 - Percent Yield and Percent Purity

The percent yield, which serves to measure the effectiveness of a synthetic procedure, is calculated by dividing the actual yield of the product (in grams) by the theoretical yield (in grams).

Percent Yield   =	Actual Yield of Product (in grams) x 100%
	Theoretical (maximum possible) Yield of Product

Lithium chlorate decomposes upon heating to form lithium chloride and oxygen gas according to the equation:

2 LiClO3 ---> 2 LiCl + 3O2

A) Determine the mass of oxygen gas that could be produced by the decomposition of 24.8 g of lithium chlorate.

24.8 g LiClO3 x ( 1 mole LiClO3 / 89 g/mole ) x ( 3 moles O2 / 2 moles LiClO3) X ( 32 g/mole /1 mole O2)=13.2 g

B) In a student experiment, 4.00 g of the gas was produced in a flask containing 24.8 g of the reactant. Determine the percent yield of the student's reaction.

% yield = actual yield / theoretical yield x 100
= 4 g O2 / theoretical yield [ANSWER in A] x100
= 4/13.2 x 100=30.3%

Percent purity is the ratio of the mass of pure substance to the mass of impure substance. 

Percent Purity =	Mass of the Pure Product
	Mass of the Impure Product Obtained

                                                                                                        


Suppose you have 0.500 g of a substance you believe is pure and you determine that it contains 0.300 g of the substance you are looking for.  So your sample is (0.300/0.500) x 100% pure = 60%