# HONORS CHEMISTRY Feb 27, 2012. Brain Teaser Cu + 2 AgNO 3  2 Ag + Cu(NO 3 ) 2 – How many moles of silver are produced when 25 grams of silver nitrate.

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HONORS CHEMISTRY Feb 27, 2012

Brain Teaser Cu + 2 AgNO 3  2 Ag + Cu(NO 3 ) 2 – How many moles of silver are produced when 25 grams of silver nitrate reacts with excess amount of copper? – How many grams of silver nitrate are needed to produce 50 grams of silver?

Agenda Brain Teaser Notes: Limiting Reactants Work on Mixed Stoichiometry Practice Worksheet 2 Homework – Complete Worksheet

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

2H 2 + O 2  2H 2 O What is the limiting reactant?

Limiting Reactants 2H 2 + O 2  2H 2 O 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 H 2 + O 2  H 2 O – 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 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 C 6 H 10 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) CaCl 2 + Na 2 CO 3  CaCO 3 + 2NaCl 5.45 g 4.55 g ? How much CaCO 3 (in g) is formed? What is the percent yield for this reaction if 3.96 g of calcium carbonate was isolated from the reaction?

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