Percent Yield and Percent Purity

Percent Yield =   actual mass produced (grams)         x 100

              theoretical mass produced (grams)

Percent Yield is found by dividing the actual mass of product formed by the mass of the product expected - aka, the product that is found by using Stoichiometry. 

For example:
If 14g of Sodium is reacted with an excess of Chlorine, then 36.5g of Sodium Chloride is produced. What is the percent yield? 

There are 3 steps.

Step 1: Balance the equation.

Na + Cl2 --> NaCl2 

Luckily for this equation, it's already balanced. So this step is done for you

Step 2: Use Stoichiometry! 

So we know that we have 14g of Sodium (Na), and we're trying to convert from grams to moles to moles to grams. In this case, were converting it from sodium to sodium chloride (NaCl2) 

so:

14g Na x 1 mole/23g x 1 mole NaCl2/1 mole Na x 94g/1 mole = 57.217g NaCl2

Step 3: Find Percent yield.

    36.5g (actual mass produced)        x 100  

57.217g (theoretical mass produced)

= 63.8% 

^ a quick video on Percent yield (in case you don't understand)

Percent Purity=   Mass of pure substance    x 100

               Mass of impure sample

Percent Purity is found by dividing the mass of the pure substance by the mass of the impure sample, and then multiplying by 100. Only the pure part of the sample will react. Before we can use stoichiometry to find out how much of the product will form, we need to know how much of the reactant is pure - and able to react.

For example:

If a 9.2g sample of metal ore contains 3.2g of Copper, what is the percent purity?

So the mass of the pure substance = 3.2g of copper.

The mass of the impure sample = 9.2g of metal ore.

Percent Purity =  3.2g    x 100 = 34.8% pure.

                          9.2g 

unfortunately could not find any you tube videos on percent purity but please enjoy this picture of a polar bear