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Mole Calculations and Stoichiometry in Chemistry

Learn to calculate molar mass, moles, and volume in chemistry through examples and dimensional analysis. Understand the concept of limiting reactants.

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Mole Calculations and Stoichiometry in Chemistry

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  1. Video 2.1 Moles and Molar Mass

  2. Objectives By the end of this video you should be able to… Calculate the molar mass of an element or a compound.

  3. Stoichiometry • The Mole represents a specific amount of any substance. • It always measures 6.02x1023 particles such as atoms and molecules.

  4. The Mole = 6.02x1023 • The mole is based on the fact that 12 grams of Carbon-12 has a mole of atoms. • A mole means you have 6.02x1023 particles.

  5. Molar Mass • Molar Mass (aka gram formula mass or molecular mass) is the mass of one mole of a substance. • Element’s molar masses are reported on the periodic table.

  6. Molar Mass Examples: Elements • What is the molar mass of iron? • What is the molar mass of copper? 55.8 g/mol 63.5 g/mol

  7. Molar Mass Examples: Compounds

  8. Objectives Now you should be able to… Calculate the mass of an element or a compound.

  9. Video 2.2 Calculating Moles

  10. Objectives By the end of this video you should be able to… Use dimensional analysis to calculate the moles of a substance.

  11. Example 1 Calculate the mass of 6.70 moles of carbon.

  12. Example 2 Calculate the mass of 0.023moles of lithium.

  13. Example 3 Calculate the mass of 25.02 moles of Ca3(PO4)2.

  14. Example 4 Determine the number of moles in 8.0 grams of Boron.

  15. Example 5 Determine the number of moles in 0.567 grams of Helium.

  16. Example 6 Find the number of moles in 1230 grams of MgSO4.

  17. DA pointers summarized • Start with the number given as a numerator over 1. • MULTIPLY by a new fraction • Place a conversion with the same unit on the denominator of the new fraction. • Multiply numerators, divide denominators. (maybe pause and copy all this?)

  18. Objectives Now you should be able to… Use dimensional analysis to calculate the moles of a substance.

  19. Video 2.3 Molar Volume and Particles

  20. Objectives By the end of this video you should be able to… Use dimensional analysis to calculate the moles of a substance based on molar volume and particles.

  21. Mole Road Map

  22. Atom versus molecule • H2O • CO2 Atoms are one particle of an element. Molecules are multiple atoms stuck together that forms a compound.

  23. Examples 1. a. Calculate the number of molecules in 4.37 moles of Lithium sulfide. b. Calculate the number of atoms in the sample

  24. Examples 2. What is the volume of 7.89 moles of He gas at STP?

  25. Examples 3. a. How many molecules are present in 79.80 Liters of P2O5 gas at STP? b. How many atoms are present in the sample?

  26. Examples 4. How many moles are present in 5.67x1024 molecules of H2O(l)?

  27. THINK Why do chemists use moles to measure substances? Why aren’t grams, liters and molecules enough?

  28. Objectives Now you should be able to… Use dimensional analysis to calculate the moles of a substance based on molar volume and particles.

  29. Video 2.4 Moles to Coefficients

  30. Objectives By the end of this video you should be able to… Use dimensional analysis to calculate the moles of various substances in a chemical reaction. Determine if a substance is excessive or a limiter.

  31. Reactions Mix + 2 Eggs + 1 cup water = Cake ReactantsProducts 2 Mix = 2 Cakes 6 Eggs = 3 Cakes

  32. Coefficients 4Al + 3O2 2Al2O3 reactants products Coefficients: How many moles of the substance are needed in a reaction.

  33. Relating Moles • To relate moles of one substance to another, simply create a proportion: 4Al + 3O2 2Al2O3 • If 3 moles of oxygen react, how many moles of Aluminum oxide form? • If 4 moles of aluminum react, how many moles of oxygen are needed? • If 4 moles of aluminum oxide are formed, how many moles of oxygen were used? • If 8 moles of aluminum react, how many moles of oxygen are needed? 2 3 6 6

  34. Example 1 16 Al + 3S8 8Al2S3 If 2.50 moles of sulfur react, how many moles of aluminum sulfide form?

  35. Example 2 16 Al + 3S8 8Al2S3 If 3.75 moles of aluminum react, how many moles of sulfur are needed?

  36. THINK Why do chemists use moles to measure substances? Why aren’t grams, liters and molecules enough?

  37. Video 2.5 Limiting Reactants

  38. Limiting Reagents • Given: 20 11 36 • 1 sandwich = 2 1 3 How many sandwiches can I make if I used all of the bread with unlimited other resources? How many sandwiches can I make if I used all of the cheese with unlimited other resources?

  39. Limiting Reagents • Given: 20 11 36 • 1 sandwich = 2 1 3 3. How many sandwiches can I make if I used all of the ham with unlimited other resources? 4. How many sandwiches can I make if I used only what is given? 5. What ingredient was the limiter? Why?

  40. Limiting Reagents Examples 1. S + 3F2 SF6 Suppose you have 4 moles of sulfur and 2 moles of fluorine, which is the limiter and which is in excess? How many moles of SF6 can be produced? 4S produces 4 SF6 2F2produces 0.6 moles of SF6 (F2 Limiter!)

  41. Limiting Reagents Examples 2. 2NH3 + CO2 (NH2)2CO + H2O If 637.2 grams of ammonia react with 1142 grams of carbon dioxide, find the limiter and the amount of urea produced.

  42. Limiting Reagents Examples 4. 5Ca + V2O5 5CaO + 2V 1.96x103 grams of calcium react with 1.54x 103 grams of V2O5. Find the limiter and the amount of V produced.

  43. Objectives Now you should be able to… Use dimensional analysis to calculate the moles of various substances in a chemical reaction. Determine if a substance is excessive or a limiter.

  44. Video 2.6 Molarity and Dilutions

  45. Objectives By the end of this video you should be able to… Calculate the molarity of a solution. Calculate the molarity of a solution after it is diluted.

  46. Concentration • Concentrated solutions contain large amounts of solutes dissolved in the solvent. • Dilute solutions contain small amounts of solutes dissolved in solvent. Which is concentrated?

  47. Molarity • The amount of solute (dissolvable substance) in a solvent (does the dissolving like water) is known as concentration and can be represented many ways. • Molarity is the moles of solute per liter of solution. Find this on your reference tables! • The units for molarity are mol/L ormol.L-1or just M. If you don’t know what this means, maybe write a note to ask me in class…

  48. mol of solute L of solution M = Molarity (M) • Because volume is temperature dependent, molarity can change with temperature.

  49. Examples can be done without a calculator! • If 3.0 moles of NaCl are dissolved in 6.0L of water, what is the molarity? • If 29 grams of NaCl are dissolved in one liter of water, what is the molarity? 3moles/6L = 0.50M 29g/58g = 0.50moles 0.5moles/1L = 0.50M

  50. Examples may need a calculator or can be estimated • If 100. grams of KF are dissolved in 300.ml of water, what is the molarity? • Calculate the volume needed to create a 2.0M solution with 3.5 moles of Li2O. 100g/58.1g =1.72mol 1.72mol/.300L = 5.70M 2.0M=3.5mol/x X = 1.8L

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