1. Mass Relationships in Chemical Reactions Chapter 3

2. Objectives 2.0 Define key terms and concepts. 2.1 Calculate the number of molecules of a compound or element. 2.2 Calculate the percent concentration for each element in a compound. 2.3 Determine the empirical molecular for a compound given the amount of each element present. 2.4 Balance chemical equations. 2.5 Convert between grams and moles.

3. Objectives 2.6 Identify the stoichiometric relationship between chemicals using a chemical reaction. 2.7 Calculate theoretical yield using stoichiometry. 2.8 Determine the limiting reagent in a reaction. 2.9 Calculate the percent yield for a reaction.

4. Avogadro's Number and The Mole Mole ▫The unit by which chemists count atoms and molecules. ▫Indicated in formulas by the letter n. Avogadro’s Number ▫Number of molecules in one mole of a substance. ▫6.02 x 10 23 molecules = 1 mole

5. Avogadro's Number and The Mole

6. Molar Mass The mass of one mole of a substance. Obtained by adding together the molar masses of the elements present. Can be used to convert between moles and grams of a substance.

7. Calculate the molar mass for the following compounds. NaCl MgBr 2 H 3 PO 4 CH 4 Ca(NO 3 ) 2 N 2 O 2

8. Mass of Element Moles of Element Atoms of Element Mass of Element ÷ Molar Mass Moles x Molar Mass Moles x Avogadro's Number Molecules ÷ Avogadro's Number Molar Conversions

9. If there are 9.8g of NaCl in a salt shaker, how many moles are present? How many molecules are present?

10. How many moles of Mg(NO 3 ) 2 are present if you have 54.36g of the compound? How many molecules of the compound are present?

11. How many molecules of CaBr 2 are present if you have 4.9g of the compound?

12. Mass of each element in a compound. Can be used to help determine the purity of a compound after synthesis. Percent Composition n x molar mass of element Molar mass of compound x 100 =

13. Calculate the percent composition for each of the elements in the following compounds: NaCl CaBr 2

14. Calculate the percent composition for each of the elements in the following compounds: Mg(NO 3 ) 2 H 2 SO 4

15. Empirical Formula The simplest whole number ratio of atoms of each element present in a compound.

16. Steps for Determining an Empirical Formula 1. Start with the number of grams of each element, given in the problem. ▫If percentages are given, assume that the total mass is 100 grams so that the mass of each element = the percent given. 2. Convert the mass of each element to moles. 3. Divide each mole value by the smallest number of moles calculated. 4. Round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula. ▫If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same factor to get the lowest whole number multiple.  e.g. If one solution is 1.5, then multiply each solution in the problem by 2 to get 3.

17. A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the empirical formula of the compound?

18. What is the empirical formula for a compound which contains 0.0134g of iron, 0.00769g of sulfur and 0.0115g of oxygen?

19. Acrylic Acid is used the manufacturing of plastics. It’s composition is 50.5% C, 5.6% H, and 44.4% O by mass. What is its empirical formula?

20. NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O. Calculate the empirical formula of NutraSweet and find the molecular formula. (The molar mass of NutraSweet is 294.30 g/mol)

21. Two compounds have the same composition: 85.62% C and 14.38% H. What is the empirical formula for these compounds? What are the molecular formulas if the compounds have molar masses of 56.06amu and 28.03amu?

22. What Are Your Questions?

23. Chemical Reactions and Chemical Equations Chemical Reaction ▫Process by which a substance is changed into one or more new substances Chemical Equation ▫Uses chemical symbols to show what occurs during a chemical reaction ▫Must be balanced

24. REACTANTSPRODUCTS YIELDS Chemical Equations

25. When 2 moles of hydrogen gas is reacted with one mole of oxygen gas, two moles of water are produced. Write the chemical equation for this reaction.

26. When three moles of calcium hydroxide react with two moles of phosphoric acid, six moles of water and one mole of calcium phosphate are produced. Write the chemical equation for this reaction.

27. Chemical Equations

28. Tricks to Balancing the Equations If an element is present in two different compounds on both sides of the reaction, balance that element first. Treat polyatomic ions as one unit If –OH is present on the reactant side and water on the product side, balance water as H-OH. Balance lone elements or diatomic elements last

29. Balance the Following Equations Al + O 2 → Al 2 O 3 SnO 2 + H 2 → Sn + H 2 O C 2 H 6 + O 2 → CO 2 + H 2 O H 2 SO 4 + Fe → Fe 2 (SO 4 ) 3 + H 2

30. Balance the Following Equations Fe 2 O 3 + H 2 SO 4 → Fe 2 (SO 4 ) 3 + H 2 O H 2 SO 4 + LiOH  H 2 O + Li 2 SO 4 NH 3 + O 2  H 2 O + N 2 Ca + H 2 O → Ca(OH) 2 + H 2

31. The reaction of potassium permanganate with hydrochloric acid yeilds potassium chloride, manganese (II) chloride, water, and chlorine gas. Write the balanaced chemical equation for this reaction.

32. Stoichiometry The quantitative study of reactants and products in a chemical reaction. Can relate moles of one compound to moles of another compound using a chemical equation to determine Theoretical Yield, or how much product you would expect to produce.

33. Stoichiometry Mass of Compound A Moles of Compound A Moles of Compound B Mass of Compound B Mass of A ÷ Molar Mass of A Moles of B x Molar Mass of B Use chemical equation to determine molar relationship

34. Al + O 2 → Al 2 O 3 2.6 moles of aluminum reacts with oxygen gas to produce aluminum oxide. How many moles of aluminum oxide are produced?

35. H 3 PO 4 + Mg(OH) 2  Mg 3 (PO 4 ) 2 + H 2 O 6.5g of phosphoric acid reacts with magnesium hydroxide to produce magnesium phosphate and water. How many moles of water are produced?

36. 13.6 grams of carbon dioxide are produced in the following reaction: CH 4 (g) + O 2 (g) → CO 2 (g) + H 2 O (g) How many grams of CH 4 were required to produce this amount of CO 2 ?

37. Oxygen gas and hydrofluoric acid are produced when fluorine gas is reacted with water. F 2(g) + H 2 O (l)  HF (g) + O 2(g) If 24.8g of fluorine gas are reacted with excess water, how many grams of oxygen can be produce?

38. Limiting Reagents ▫The reactant that is used up first in the reaction ▫Determines the amount of product that will be produced. Excess Reagents ▫Will not be fully used up during the reaction because it is present in excess of the limiting reagent

39. If 4 moles of aluminum and 5 moles of oxygen are reacted as represented in the following reaction: Al + O 2 → Al 2 O 3 What is the limiting reagent?

40. If 12.6g of phosphoric acid are reacted with 25.3 g of magnesium hydroxide in the following reaction: H 3 PO 4 + Mg(OH) 2  Mg 3 (PO 4 ) 2 + H 2 O What is the limiting reagent?

41. If 18.5 grams of CH 4 are reacted with 5.9g of O 2 in the following reaction: CH 4 (g) + O 2 (g) → CO 2 (g) + H 2 O (g) How many grams of CO 2 will be produced?

42. If 18.6g of AgNO 3 is reacted with 3.6 moles of H 2 SO 4 in the following reaction: AgNO 3 (aq) + H 2 SO 4 (aq) → Ag 2 SO 4 (s) + HNO 3 (aq) How many grams of silver sulfate will be produced?

43. If 2.3 grams of silver nitrate are reacted with 6.9g of sulfuric acid according to the following reaction, AgNO 3 (aq) + H 2 SO 4 (aq) → Ag 2 SO 4 (s) + HNO 3 (aq) How many grams of silver sulfate are produced?

44. Reaction Yield Actual Yield ▫The amount of chemical actually obtained from the reaction Percent Yield Actual Yield Theoretical Yield x 100 =

45. What is the percent yield for the synthesis of aluminum oxide if you calculate the theoretical yield to be 13.6g but you produce 10.5g experimentally?

46. What Are Your Questions?