% Yield and % Purity In stoichiometric calculations

% 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…

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)

% 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.

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

% 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

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?

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?

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?

% 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.

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

%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

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?

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

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)