UNIT VII Percentage Yield. VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Percentage Yield : is used to describe the amount of product actually obtained.

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Presentation transcript:

UNIT VII Percentage Yield

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Percentage Yield : is used to describe the amount of product actually obtained as a percentage of the expected amount. 2 reasons: 1. reactants may not all react 2. some products are lost Yield : is the amount made in a chemical reaction

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: THREE TYPES of YIELD 1. Actual Yield – what you get in the lab when the chemicals are mixed 2. Theoretical Yield – what the balanced equation says you should make 3. Percent Yield - Actual Yieldx 100% Theoretical Yield

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY:  There are two possible situations: 1. Actual amount of PRODUCTS FOUND is LOWER than the value expected. To solve: calculate “amount of product expected” using stoichiometry then multiply ( x ) “amount of product expected” by the decimal equivalent of the % yield or % purity

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: 2. Actual amount of REACTANTS NEEDED is GREATER than the value expected To solve: calculate the “amount of reactant needed” using stoichiometry then divide (÷) “amount of reactant needed” by the decmial equivalent of % yield or % purity

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #1 When 45.8g of potassium carbonate, K 2 CO 3 are reacted completely with an excess of HCl, 46.3 g of KCl are produced. Water and CO 2 also are formed. Calculate the theoretical yield and the percent yield of KCl.

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #2 2Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu When 3.92 g of Al are reacted with excess copper(II) sulfate, 6.78 g of copper is produced. a) What is the actual yield?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #2 (continued) 2Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu When 3.92 g of Al are reacted with excess copper(II) sulfate, 6.78 g of copper is produced. b) What is the theoretical yield?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #2 (continued) 2Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu When 3.92 g of Al are reacted with excess copper(II) sulfate, 6.78 g of copper is produced. c) What is the percentage yield?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #2 (continued) 2Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu When 3.92 g of Al are reacted with excess copper(II) sulfate, 6.78 g of copper is produced. d) If you started with 9.73g of Al how much copper would you expect?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #3 What mass of Fe 2 O 3 is produced when 2.30 g of FeCO 3 are reacted with an excess of O 2 according to the reaction: 4FeCO 3 + O 2 → 2Fe 2 O 3 + 4CO 2, if the reaction has a 67.0 % yield?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: Ex: #4 What mass of CO 2 is required to make 8.00g of K 2 CO 3(s) according to the reaction: 4KO 2(s) + 2CO 2(g) → 2K 2 CO 3(s) + 3O 2(g) if the reaction has a 85.0% yield?

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: OPTIONAL: Percentage Purity : the amount of pure chemical actually present in a sample as a percentage of the amount of the impure chemical present Percentage Purity= mass of pure reactant x 100% mass of impure reactant

VII.5 PERCENTAGE YIELD AND PERCENTAGE PURITY: % Purity calculations fall into 3 categories: 1. find the % purity given mass of reactants used and mass of product formed 2. find the mass of product formed, given the mass of reactant used and the percentage purity 3. find the mass of reactant used, given the mass of product formed and the % purity