Percent Yield and Percent Purity!

Percent Yield=   actual mass produced (grams)    x 100

           theoretical mass produced (grams)

The percent yield is found by dividing the actual mass of product formed by the mass of the product expected (this is found with stoichiometry).

Because not all the products will be used, the actual mass of product formed is always less than what was first expected.

E.g. If 12.5g of copper are reacted with an excess of chlorine, then 25.4g of copper(II)chloride are obtained. Calculate the percent yield. 

First, balance the equation:

1Cu + 1Cl2 > 1CuCl2

We can use the 12.5g of copper to calculate the theoretical mass produced. 

12.5g Cu x 1 mol Cu/63.5g x 1mol CuCl2/1 mol Cu x 134.5g/1 mol CuCl2 = 26.48g

So we know that IN REALITY, 25.4g of CuCl2 were produced, this is our actual mass produced.

Percent Yield=   25.4    x 100

                 26.5

So our percent yield is 95.9%. 

 

Percent Purity=   Mass of pure substance    x 100

                     Mass of impure sample

Only the pure part of the sample will react. So, before we can calculate how much product will form, we first need to know how much of the reactant is pure and available to react.

If a 5.67g sample of metal ore contains 4.65g of Nickel, what is the percent purity?

Percent Purity=   4.65    x 100

                     5.67

So our percent yield is 82.0%. 

GOOD DAY!