1. I’m hiring! Homework Graders Pay = 1 extra credit point/10 papers graded Qualifications: –No TUs, BD, LD –Availability before/after school or 5 th period lunch. –No nepotism/cronyism will be tolerated

2. HOMEWORK DUE MIErCOLES If you haven’t done so already, read chapter 3! P114 - 115: #22, #32, #34

3. Stoichiometry The quantitative study of chemical reactions

4. Use stoichiometry to answer these questions: How much product will form from a given amount of reactants? How much of the reactants is necessary to form a given amount of product?

5. Stoichiometric Steps

6. Step 1 Predict products of a reaction if they are not given to you Balance the coefficients of the reaction

7. Step 2 Use molar conversion to change whatever is given (volume, mass or concentration) to moles

8. Step 3 Use the molar ratio from the balanced reaction to convert the moles of what is given to the moles of what’s asked for.

9. Step 4 Use conversion factors (moles  mass, volume or M) to change the moles of what is asked for to the proper unit

10. Calculate the volume of NH 3 formed at STP when 5.0 kg of H 2 react with excess N 2 to form NH 3

11. Calculate the number of molecules of oxygen gas required to burn 3.0 g of C 5 H 10 O 5

12. Calculate the mass of solid product formed when 18.4 g of MgBr 2 is combined with a solution containing excess K 2 CO 3.

13. Limiting Reactant The reactant that gets used up The reactant that determines the amount of product formed

14. Excess Reactant The reactant that Does Not get used up

15. When I give you quantities of more than one reactant:  You must figure out which one is limiting

16. 3A + 2B  A 3 B 2 Which reactant is limiting? Do Step 1 and then Step 2 for both A & B. Pick A (your chemistry grade?) Use the molar ratio that relates A to B to determine how much of B would be needed to completely use up the moles of A If there are more than enough moles of B, A is limiting If there not enough moles of B, then B is limiting Use limiting reactant for steps 3 & 4

17. Calculate the mass of glucose (C 6 H 12 O 6 ) formed when 880 g of carbon dioxide is combined with 720 g of water in photosynthesis

18. Calculate the mass of BaSO 4 formed when 104 g of BaCl 2 is combined with 250 mL 1.00 M K 2 SO 4

19. How to make a BLT sandwich: 2 PB (pieces bread) 3 TS (tomato slices) 5 BS (bacon slices) 2 LL (lettuce leaves) ++ +

20. So reaction is: 2 PB + 3 TS + 5 BS + 2 LL  1 BLT 1 BLT

21. Masses of reactants + product: 1 PB = 50.0 g 1 TS = 60.0 g 1 BS = 20.0 g 1 LL = 5.0 g 1 BLT = 390.0 g

22. How many BLTs? PB = 3,356.7 g TS = 4,789.2 g BS = 2,789.4 g LL = 789.2 g Get answer in significant digits and then round down to whole number of BLTs.

23. Theoretical Yield The amount determined through stoichiometry The amount solved for on paper

24. Experimental Yield The amount obtained in the lab Actual yield

25. Percent yield % Yield = (Exp/Theo) x 100 %

26. 68 g NH 3 was obtained when 140 g of N 2 reacts with excess H 2. Calculate percent yield.

27. 510 g PH 3 was obtained when 0.62 kg of P 4 reacts with excess H 2. Calculate percent yield.

28. 4.61 g of lead(II)iodide was obtained when 66.2 g of lead(II)nitrate was added to 750 ml 0.10 M potassium iodide. Calculate the % yield.

29. Calculate the volume of oxygen gas at STP required to burn 12 kg of erythrose (C 4 H 8 O 4 )

30. Determine the volume of NH 3 formed at STP when 2.0 x 10 27 molecules N 2 reacts with 4.0 kg of H 2 :

31. Determine the volume of O 2 released at STP when 32 kg of Fe 2 O 3 is purified making Fe & O 2

32. Calculate the mass of solid product formed when 41.6 g of barium chloride is added to 250 ml of 0.40 M potassium sulfate giving a 50.0 % yield:

33. Calculate the mass of solid product formed when 2.00 g of calcium bromide is added to 250 ml of 0.40 M sodium sulfate: