1. % Yield and % Purity In stoichiometric calculations

2. % Yield and % Purity ❖ Sometimes 100% of the expected amount of products cannot be obtained from the reaction ❖ Actually – I’ve never done an experiment that even provided ½ of the expected yield…

3. Reduced Yields ❖ The reactants may not ALL react ❖ this may be because not all the pure material actually reacts or ❖ the reactants may be less than 100% pure ❖ Some of the products are lost during the procedure (solvent extract, etc)

4. % Yield ❖ If you know the expected amount of product based on stoichiometric calculations AND you measure the actual mass of the product formed, you can calculate the PERCENT YIELD of your experiment.

5. % Yield % Yield = mass of product obtained x 100% mass of product expected

6. % Yield Calculations ❖ Find the %yield, given the mass of reactant used and mass of product formed ❖ Find the mass of product formed, given the mass of reactant used and the %yield ❖ Find the mass of reactant used, given the mass of product formed and the %yield

7. Example 1: ❖ When 15.0 g of CH4 is reacted with an excess of Cl2 according to the reaction CH4 + Cl2  CH3Cl + HCl a total of 29.7g of CH3Cl is formed. What is the % yield of the reaction?

8. Example 2: ❖ What mass of K2CO3 is produced when 1.50g of KO2 is reacted with an excess of CO2 according to the reaction 4KO2(s) + 2CO2(g)  2K2CO3(s) + 3O2(g) If the reaction has a 76.0% yield?

9. Example 3: ❖ What mass of CuO is required to make 10.0g of Cu according to the reaction 2NH3 + 3CuO  N2 + 3Cu + 3H2O If the reaction has a 58.0% yield?

10. % Purity ❖ If less than the expected amount of a product is produced it is possible reactants which are less than 100% pure were used. In this case PERCENTAGE PURITY of the REACTANT is calculated.

11. % Purity ❖ % Purity = mass of pure reactant x 100 mass of impure reactant

12. %Purity Calculations ❖ Find the %purity, given the mass of reactant used and mass of product formed ❖ Find the mass of product formed, given the mass of reactant used and the %purity ❖ Find the mass of reactant used, given the mass of product formed and the %purity

13. Example 1: ❖ If 100.0g of FeO produce 12.9g of pure Fe according to the reaction 2FeO + 2C + O2  2Fe + 2CO2 What is the percentage purity of the FeO used?

14. Example 2: ❖ What mass of pure sodium carbonate Na 2 CO 3, can be formed by heating and decomposing 5.00g of 79.4% pure “trona”, Na 5 (CO 3 ) 2 (HCO 3 )2H 2 O according to the equation 2Na 5 (CO 3 ) 2 (HCO 3 )2H 2 O  2 Na 2 CO 3 + CO 2 + 5H 2 O

15. Example 3: ❖ What mass of impure zinc metal having a purity of 89.5% is required to produce 975mL of hydrogen gas at STP according to the reaction Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)