Chapter_3 - Chapter 3 Mass Relationships in Chemical...

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Chapter 3 Mass Relationships in Chemical Reactions This chapter uses the concepts of conservation of mass to assist students in gaining an understanding of chemical changes. Upon completion of Chapter 3, your students should be able to: 1) Write the conversion between grams and atomic mass units (AMU’s). 2) Calculate the average atomic mass given the mass and natural abundance of each isotope. 3) Write Avogadro’s number. 4) Determine the number of objects present in a given number of moles. 5) Write the conversion of mass, number of moles, and number of atoms (molecules) for an element (compound). 6) Calculate the molecular mass and molar mass given the molecular formula. 7) Sketch the main components of a mass spectrometer and describe how they are used. . 8) Compute the percent composition (mass percent) given the chemical formula for an ionic or molecular compound. 9) Describe the experimental procedure used to determine empirical formulas. 10) Calculate the molecular formula given the mass of each element present (or mass percent of each element) and the compound’s molar mass. 11) Balance chemical equations. 12) Interpret the meaning of chemical equations in terms of molecules, moles, and masses. 13) Distinguish between products and reactants in a chemical equation. 14) Predict the products formed by combustion reactions. 15) Use stoichiometric methods to predict the mass (number of moles) of the products formed given the mass of each reactant (number of moles of each reactant). 16) Use stoichiometric methods to deduce the limiting reagent, excess reagent, the amount of expected products produced, and the amount of excess reagent left over upon completion of the reaction given the mass (number of moles) of each reactant in the chemical equation. 17) Use stoichiometric methods to predict the theoretical yield and percent yield given the mass (number of moles) of each reactant and the actual yield of a reaction. 18) Calculate the mass (number of moles) of each reactant required given the percent yield and the mass (number of moles) of products desired. Section 3.1 Atomic Mass Sometimes atomic weight and atomic mass are used interchangeably. However, to decrease confusion and to be consistent, the term atomic weight is not used. Knowledge of atomic mass unit (amu) is especially important for students who plan to enroll in materials science courses where the mass contained in a unit cell in the solid state is often determined. A helpful comparison can be made between calculating the average atomic mass and the semester grade for a course. For example, if 30% of the grade is based on the midterm, 20% on laboratory and 50% on the final and a student earns 80 on the midterm, 90 in laboratory, and a 96 on the final, the
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student’s grade is (0.30) (80) + (0.20) (90) + (0.5) (96) = 90. A similar calculation can be done for the average atomic mass of C (see pages 80). Average atomic mass of C = (0.9890) (12.00000 amu) + (0.0110) (13.00335 amu)
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This note was uploaded on 02/08/2012 for the course CHEM 161 taught by Professor Shaklovich during the Spring '10 term at Harvard.

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Chapter_3 - Chapter 3 Mass Relationships in Chemical...

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