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Concept Presentation Limiting Reactants

Concept Presentation Limiting Reactants. Namrta Bhardwaj. Background Information. Prerequisite knowledge should include nomenclature balancing chemical equations. Mole to mole and mass to mole calculation It is important that students understand the law of conservation of mass

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Concept Presentation Limiting Reactants

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  1. Concept PresentationLimiting Reactants Namrta Bhardwaj

  2. Background Information • Prerequisite knowledge should include • nomenclature • balancing chemical equations. • Mole to mole and mass to mole calculation • It is important that students understand the law of conservation of mass • Students should also be skilled in using ratios and conversion factors in calculations.

  3. Demonstration Video

  4. Curriculum Expectations Overall expectations: • D2. Investigate quantitative relationships in chemical reactions, and solve related problems • D3. Demonstrate an understanding of the mole concept and its significance to the quantitative analysis of chemical reactions

  5. Specific expectations • D2.1 Use appropriate terminology related to quantities in chemical reactions, including, but not limited to: stoichiometry, percentage yield, limiting reagent, mole, and atomic mass [C] • D2.5 Calculate the corresponding mass, or quantity in moles or molecules, for any given reactant or product in a balanced chemical equation as well as for any other reactant or product in the chemical reaction [AI] • D2.6 Solve problems related to quantities in chemical reactions by performing calculations involving percentage yield and limiting reagents [AI] • D3.4 Explain the quantitative relationships expressed in a balanced chemical equation, using appropriate units of measure (e.g., moles, grams, atoms, ions, molecules)

  6. Place in the Curriculum

  7. Placement Within the Unit Counting Atoms and Molecules: The Mole • The Avogadro Constant and the Mole • Molar Mass Chemical Proportions in Compounds • Percentage Composition • Empirical Formula of a Compound • Molecular Formula of a Compound Quantities in Chemical Reactions • Stoichiometry • Limiting Reactant • Percentage Yield

  8. Misconceptions / Learning Difficulties When the mass of both reactants is given students have difficulty recognizing that one of the masses is limiting and the other mass is in excess. • randomly select one of the given masses as limiting or excess • assume that the masses are in the correct mole ratios students • assume the smaller mass is the limiting reagent. • Need to point out these are not trick questions • Important to stress the common steps in converting masses into amounts in moles in order to relate to mole ratios in balanced equations.

  9. Demonstrate Reaction • Which reactant is limiting and which is in excess reactant?

  10. Demonstrate Mass to Mole Relationship Use copper chloride reacting with Aluminum to illustrate a mass to mole relationship

  11. Misconceptions • If reactants are in the same physical state the reaction reaches completion when both reactants are totally converted Or • If the reactants are in two different physical states (solid and liquid) the reaction reaches completion when the entire solid is consumed.

  12. Reaction of Mg with HCl

  13. Misconceptions • Students have limited view of chemical system since they have been taught to consider a reaction system as: reactants -> products • rewrite equation as: Reactants -> Products + excess reactant

  14. Gizmo Activity

  15. Gizmo Activity

  16. Gizmo Activity

  17. Supporting Diverse Student Needs • Challenge gifted students -How many grams of a particular starting material will remain at the end of a reaction? • Encourage gifted students to develop their own methods for solving problems - do not follow given format • ELL students have difficulty understanding verbal explanations - may benefit from writing out the thought process used in solving sample problems. • Students that required more support may be given more scaffolding and support in questions. • Have students make common sense prediction when solving problems.

  18. Day 1

  19. Day 1

  20. Day 2

  21. Days 3,4 and 5

  22. Applications and Societal Implications • Careers in Chemistry – Chemical Engineer • Cooking recipes, industrial reactions, prescription drug dosages, manufacturing, building (constructions) • The amount of carbon on earth is the ultimate limiting reagent for the number of people the earth can have and in the sense that carbon is our "food"... the land area of the earth is a "limiting reagent" that will limit our population before carbon does.... L. H. Holmes Jr.

  23. Advanced Preparation • Day 1 Refer to Interactive Demonstrations for Mole Ratios and Limiting Reagents (annotated reference 1) and prepare material for the lab accordingly. Refer to How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar (annotated reference 6) and prepare material for the lab accordingly. • Day 5 Refer to pg 165 of the Nelson teacher’s resource for percentage yield in a chemical reaction lab and prepare material for the lab accordingly.

  24. Safety Considerations • Remember to always wear safety goggles. Reaction of Na with water demo • Never use a piece of sodium larger than a ½ pea r. • The reaction should be carried out behind a clear safety barrier or at a distance from the students Reaction of Copper (II) chloride with Aluminum • Copper(II) chloride is toxic by ingestion and irritating to skin • Aluminum will also react with the solution to produce hydrogen gas. Flames should not be used in this investigation Reaction of baking soda with vinegar • Avoid getting baking soda or vinegar in eyes

  25. Annotated References Breyfogle, Bryan. (2006) Interactive Demonstrations for Mole Ratios and Limiting Reagents. Journal of Chemical Education, 85 (5), 741. The demonstration of the mole and mass ratios for the reaction of CuCl2 and Al were obtained from this article. Clyde, Dillard R. (1972) Two Lecture Experiments Demonstrating Limiting Quantities. Journal of Chemical Education, 49 (12), A694. Resource used for conducting limiting reactant experiment using Mg and HCl. Gauchon, Laure, et al. (2007) Learning About Stoichiometry: From Students’ Preconceptions to the Concept of Limiting Reactant . Chemistry Education Research and Practice, 8 (4), 362-375. Article discusses many misconceptions that student encounter with studying limiting reactants. Holmes, L. H. Jr. (1998) Limiting Reagent and Kinetics: Social Implications and Malthus' Prediction. Journal of Chemical Education, 75 (8), 1004. Interesting article that discusses food supply and land area in terms of limiting reagents. Jenkins, Frank, et al. (2002). Chemistry 11. Toronto: Nelson. (course textbook) Journal’s Editorial Staff (1997). How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar. Journal of Chemical Education, 74 (2), 1328A-1328B. Article used for the Baking soda and vinegar lab. Resource used for conducting limiting reactant experiment using vinegar and baking soda. Kalanter, A.H. (1985) Limiting Reagent Problems Made Simple for Students. Journal of Chemical Education, 62 (2), 106. Article used to for the ICE method for solving limiting reactants. Mustoe, Frank, et al. (2201). Chemistry 11. Toronto: McGraw-Hill Ryerson. (course textbook)

  26. Annotated References Websites: http://www.chalkbored.com/lessons/chemistry-11.htm good power point presentation on limiting/ excess reactants, also the chart method for solving limiting reactant problems was taken from this site http://www.youtube.com/watch?v=xk7PSpFC7NI&feature=related demonstration of the flaming table and whoosh bottle http://www.chemprofessor.com/ flow chart method was obtained from this site

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