1. 1. Define “the law of conservation of mass”

2. Stoichiometry The “final boss” of Chem R

3. Objectives  12.1a Describe how chemists use balanced chemical equations.  12.1b Describe the quantities you can use to interpret a balanced chemical equation.  12.1c Identify the quantities that are always conserved in chemical reactions.

4. Hey Kids!

5. Tricycles!  Frames, Handlebars, pedals, wheels, and a seat go in to the making of a tricycle  How many wheels do you need if you want to make 640 tricycles?

6. Stoichiometry  The calculation of quantities in chemical reactions is called stoichiometry  It’s pronounced STOY-KEE-AH- MET-REE!

7. What it means  Remember balancing equations? That can be used to account for: NUMBER OF ATOMS N 2 + 3H 2  2NH 3  2 Atoms N + 6 Atoms H  2 Atoms N and 6 Atoms H

8. They can also account for: NUMBER OF MOLECULES N 2 + 3H 2  2NH 3  1 Molecule N 2 + 3 Molecules H 2  2 Molecules NH 3 Use coefficients!

9. They can also account for: MOLES N 2 + 3H 2  2NH 3  1 Mole N 2 + 3 Moles H 2  2 Moles NH 3

10. They can also account for: MASS N 2 + 3H 2  2NH 3  Convert each into mass using the coefficients and molar masses  34.0 g total mass reactants  34.0 g total mass products

11. You try 1. Balance H 2 S + O 2  SO 2 + H 2 O (Hint: Save Oxygen for last!) 2. Prove that this does not violate the law of conservation of mass!

12. Do-now:  Prove that this balanced equation does not violate the law of conservation of mass  2NaCl + Ca(NO 3 ) 2  2NaNO 3 + CaCl 2

13. Objectives  12.2a Explain how mole ratios are used in chemical calculations.  12.2b Explain the general procedure for solving a stoichiometric problem.

14. Mole Ratio  Let’s look at that equation again N 2 + 3H 2  2NH 3  A Mole Ratio is a conversion factor derived from the coefficients of a balanced chemical equation

15. Using mole ratios  How many moles of NH 3 are produced when 0.60 moles of Nitrogen reacts with Hydrogen?  1.2 mol NH 3

16. Practice  Fe 2 O 3 + 3CO  2Fe + 3CO 2  Find the mole ratio for Fe 2 O 3 : Fe.  How many moles of Fe are produced from 1.8 moles of Fe 2 O 3 ?

17. Question  If we are given this same equation N 2 + 3H 2  2NH 3  If 5.40 g of Hydrogen reacts to form ammonia, how many grams of ammonia will be produced?

18. Mass-mass conversions  When using stoichiometry for mass- mass conversions in a problem, use the following steps (Given=G, Wanted=W) 1. Mass G x = mol G

19. Question  If we are given this same equation N 2 + 3H 2  2NH 3  If 5.40 g of Hydrogen reacts to form ammonia, how many grams of ammonia will be produced?

20. Mass-mass conversions  When using stoichiometry for mass- mass conversions in a problem, use the following steps (Given=G, Wanted=W) 1. Mass G x = mol G 2. Mol G x = mol W

21. Question  If we are given this same equation N 2 + 3H 2  2NH 3  If 5.40 g of Hydrogen reacts to form ammonia, how many grams of ammonia will be produced?

22. Mass-mass conversions  When using stoichiometry for mass- mass conversions in a problem, use the following steps (Given=G, Wanted=W) 1. Mass G x = mol G 2. Mol G x = mol W 3. Mol W x = Mass W

23. Question  If we are given this same equation N 2 + 3H 2  2NH 3  If 5.40 g of Hydrogen reacts to form ammonia, how many grams of ammonia will be produced? 31 g Ammonia

24. Homework  Read Section 12.1  Complete Lesson Check, p. 389  Be ready for a lab on monday  Start reviewing old notes/chapters- YES you will receive a study guide for the final!

25. Practice  Rust forms with the equation 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s) How many grams of Fe 2 O 3 are produced when 12.0 g of Iron rusts? 17.2 grams Fe 2 O 3

26. Homework  Finish lab report: “Quantitative Analysis” Yes, must be written up! (either on computer or on a separate sheet) Include Title, Purpose, Hypothesis, Safety, Materials, Procedure, Data, Analysis questions, and 1 P conclusion. Going Further is optional, don’t worry about actually doing another lab. Lab sheet is available online, or see me after school for a copy.

27. Percent yield and limiting reactant

28. Do-now  Determine the mole ratios in the following reaction: 2Au 2 O 3  4Au + 3O 2

29. Lab Report  Finish lab report: “Quantitative Analysis” Yes, must be written up! (either on computer or on a separate sheet) Include Title, Purpose, Hypothesis, Safety, Materials, Procedure, Data, Analysis questions, and 1 P conclusion. Going Further is optional, don’t worry about actually doing another lab. Lab sheet is available online, or see me after school for a copy.

30. Do now  The first 3 students to show me a balanced reaction of sodium hydroxide and hydrochloric acid can be volunteers for my demonstration

31. Objectives  12.3a Explain how the amount of a product in a reaction is affected by an  insufficient quantity of any of the reactants.  12.3b Explain what the percent yield of a reaction measures.

32. S’mores  You want to make smores. Each S’more requires 1 Marshmallow, 1 small chocolate bar, and 2 graham crackers. If you have 85 marshmallows, 97 small chocolate bars, and 150 graham crackers, how many S’mores can you make?

33. S’mores  75, right?  Will you have ingredients left over? How many?

34. Limiting Reactant N 2 + 3H 2  2NH 3 In this example, Hydrogen is the limiting reagent because all of it is used up in the reaction Nitrogen is considered the excess reagent because it is the reactant that is not completely used up in the reaction

35. Practice  H 3 PO 4 + 3NaOH  Na 3 PO 4 + 3H 2 O  If you have 1.75 mol of H 3 PO 4 and 5 mol of NaOH, which is the limiting reactant?

36. Theoretical vs. Actual Yield  For the last reaction, how much Na 3 PO 4 should be produced? Theoretical Yield: Maximum amount of product that can be formed in a reaction  But what if you only produced Actual Yield: the amount of product that actually forms when the reaction is carried out in a laboratory

37. Percent Yield  Ratio of actual yield to the theoretical yield expressed as a percent  It is good to get a high percent yield!  Percent yield cannot be greater than 100% (or should not, at least)

38. Practice. A tough question.  When 50.0 g of silicon dioxide is heated with an excess of carbon, 32.2 g of silicon carbide is produced. What is the theoretical yield of silicon carbide of this reaction? What is the percent yield of this reaction?

39. Homework  Read 12.3, perform lesson check.  For 3 extra credit points on the upcoming chapter 12 test… complete question 81 on p. 415 Must have all work presented neatly on a separate piece of paper Must be entirely correct to get the 3 points. This is difficult and tedious, only accept the challenge if you are really up to it! (AP Chem kids, I’m looking at you!)  Speaking of the test, it is Friday!