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Learn about limiting reactants in chemistry and how they determine the maximum amount of product that can be formed in a chemical reaction. Solve practice problems and calculate percent yield.
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CHEMISTRY February 13, 2012
Brain Teaser 2HCl + Na2SO4 2NaCl + H2SO4 • If you start with 20 grams of hydrochloric acid (HCl), how many grams of sodium chloride (NaCl) will be produced?
Agenda • Brain Teaser • Grade Homework • Limiting Reactants Notes • Practice • Partner Quiz (?) • Homework • TBD
Limiting Reactants • Reactant that is completely used up in a chemical reaction • Determines the maximum amount of product that can be formed.
Limiting Reactants • Why is this important? • The quantities of products formed in a reaction are always determined by the quantity of the limiting reactant.
Limiting Reactants • Analogy: making cheese sandwiches
Limiting Reactants 2H2 + O2 2H2O What is the limiting reactant?
Limiting Reactants 2H2 + O2 2H2O What is the limiting reactant?
Limiting Reactants • How many grams of water can I make from 22 grams of hydrogen and 195 grams of oxygen? • Write a balanced chemical equation H2 + O2 H2O • What is the limiting reactant? • Answer: Do two stoichiometry calculations • Determine mass of product produced by each reactant • How do you know?
Determining the limiting reactants • The limiting reagent may not be obvious!!
Practice Problem • When copper (II) chloride reacts with sodium nitrate, copper (II) nitrate and sodium chloride are formed • Write the balanced equation for the reaction • If 15 grams of copper (II) chloride react with 20 grams of sodium nitrate, how much sodium chloride can be formed? • What is the limiting reactant? • How much of the nonlimiting reactant is left over in this reaction? • If 11.3 grams of sodium chloride are formed in the reaction described above, what is the percent yield of this reaction?
Can you really get out everything that goes in? % yield = experimental yield x 100 theoretical yield Experimental or actual yield determined in the lab Theoretical or expected yield determined by stoichiometry
Practice Problem • If 35 grams of C6H10 reacts with 45 grams of oxygen, how many grams of carbon dioxide will be formed? • What is the limiting reactant? • How much of the excess reactant is left over after the reaction ? • If 35 grams of carbon dioxide are actually formed from the reaction, what is the percent yield of this reaction?
Partner Quiz 1) CaCl2 + Na2CO3 CaCO3 + 2NaCl 5.45 g 4.55 g ? How much CaCO3 (in g) is formed? What is the percent yield for this reaction if 3.96 g of calcium carbonate was isolated from the reaction?