Launching Activity 1.Measure 5 ml of 0.01 M KMnO4 and place in a 100 ml beaker and then measure 5 ml of 0.01 M NaHSO3. 2.Slowly pour the NaHSO3 into the KMnO4 while stirring. 1.What do you observe? 2.Why is adding slowly better? 3.How could you measure the resulting precip?

UEQ How does a pharmaceutical chemist know many pills it can get from a given amount of reagents?

Chapter 12: Stoichiometry Definition: Measurement of the amount of a substance in a chemical reaction.

LEQ How is the mass relationship of a chemical reaction confirmed by the law of Conservation of Mass?

*Key: A good balanced chemical equation.* The Law of the Conservation of Mass applies: You must have the same before and after a reaction. ‘ The same by: mass, type of atoms, volume, and moles.

Conversion factors: 1 mole atoms = gam (gram atomic mass) 1 mole molecule = gmm (gram molecular mass) 1 mole compound = gfm (gram formula mass) 1 mole of any STP = 22.4 L 1 mole of anything  Avogadro’s Number  mass

Type of stoichiometric relationships 1. Mole-mole relationships: ie: How many moles of water are produced when 0.5 moles of oxygen react in an excess of hydrogen? a. Write a good balanced equation. b. From the balanced equation, write the molar ratio linking the known to the unknown in the question.

From the above question, how much hydrogen gas is left after the reaction? **NOTE: From the balanced equation, link by the molar ratio the known to the unknown. **NOTE: Oxygen is called the ‘limiting reactant’ b/c it will be used up before the other reactants are used. TPS: Practice Problem #1-2 page 371 and #’s 3-4 page 372. #’s 36,40, and 41 page 392.

2. Mass-mass Relationships: mass known  moles known  moles unknown  mass unknown mass-mole conversion molar ratio mole-mass conversion ie: How many grams of water is produced when 4.5 g of hydrogen reacts in an excess of oxygen? Write a good balance equation Convert following the flow chart.

Mass-Mass Relationships 1. Law of Conservation of Mass. 2. Mass-mass relationship based on the molar ratio of a good balanced equation. Mass know>mole know>mole unknow>mass unknow Mass-mole : mole-mole: mole-mass

3. Mass-mole or Mole-mass Relationship. mass known  moles known  moles unknown mass-mole conversion molar ratio 4. Mass-Number of particles (# atoms, molecules or compounds). Use 1 mole = Avogadro’s Number (6.02 x ). mass known  moles known  mole unknown  # mass-mole conversion molar ratio6.02 x 10 23

5. Mass-volumeand Volume-mass mass known  moles known  mole unknown  volume 6. Volume-volume Avagodro’s Principle states that any gas at STP will occupy the same volume of 22.4L (STP = Standard Temperature and Pressure) (STP = 0 o C and 1 atm) volume known  moles known  moles unknown  volume

TSP Sample When 45 g of CH 4 burns, how many L of H 2 O will yield? ans: 126 L How many liters of methane gas is burned if 320 mole of O 2 are present? ans: 3584 L

LEQ How efficient is a given chemical reaction?

% yield Definition: comparison of the actual yield to the theoretical yield. % yield = actual / theoretical x Use mass relationships to find the theoretical yield 2. Experimentation determines the actual yield. TSP: #28-29, page 387

LEQ What defines when a chemical reaction stops?

Limiting Reagent: Limiting Reagent: The amount of product that will form is defined by the reactant of least amount. Limiting reactant is defined through the comparison of the amount given to the molar ratio in a balanced equation.

Steps in Limiting Reactant Always start with a balance equation. Using the balanced equation, compare the moles of reactants given. The limiting reactant will define product.

TSP Sample When 6.7 moles of sodium reacts with 3.2 moles of chlorine gas to produce sodium chloride. What is the limiting reactant and how many moles of product will form? Write the balanced equation. Use the molar ratio between reactants to compare the amount of reactant required to react. To find the amount of product, the limiting reactant is used.

TSP Sample Given 80 g of Cu and 25 g of S to yield copper (I) sulfide, what is the limiting reactant and how much product is produced (in grams)? –Write a balanced equation. –Find the # of moles of each reactant from the given masses. –Determine, from the # of moles, which is the limiting reactant. –Use the limiting reactant to determine the amount of product produced. TSP: #23-24 page 383

TSP: Sample Mole-Mole Given: Fe 2 O 3 + 3CO  2Fe + 3CO 2 How many moles of CO is needed react with 25 formula units of Fe 2 O 3 ? ans: 75 moles Given 2.25 moles of Fe 2 O 3, how many moles of Fe will be produced? ans: 4.5 moles

TPS Sample Mole-Mass Given the same reaction as above: How many g of Fe will be produced from 2.25 moles of Fe 2 O 3 ? ans: 251 g Fe Given 5.4 g of Fe 2 O 3, how many moles of CO 2 will be produced? ans: 0.10 moles