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Chapter 3 Stoichiometry Section 3.1 Counting by Weighing EXERCISE! A pile of marbles weigh 394.80 g. 10 marbles weigh 37.60 g. How many marbles are in the pile? Avg. Mass of 1 Marble = 37.60 g = 3.76 g / marble 10 marbles 394.80 g = 105 marbles 3.76 g Copyright © Cengage Learning. All rights reserved 2 1 Section 3.2 Atomic Masses EXERCISE! An element consists of 62.60% of an isotope with mass 186.956 u and 37.40% of an isotope with mass 184.953 u. Calculate the average atomic mass and identify the element. 186.2 u Rhenium (Re) Copyright © Cengage Learning. All rights reserved 3 Section 3.3 The Mole EXERCISE! Calculate the number of iron atoms in a 4.48 mole sample of iron. 2.70×1024 Fe atoms Copyright © Cengage Learning. All rights reserved 4 2 Section 3.4 Molar Mass EXERCISE! Consider separate 100.0 gram samples of each of the following: H2O, N2O, C3H6O2, CO2 Rank them from greatest to least number of oxygen atoms. H2O, CO2, C3H6O2, N2O Copyright © Cengage Learning. All rights reserved 5 Section 3.6 Percent Composition of Compounds EXERCISE! Consider separate 100.0 gram samples of each of the following: H2O, N2O, C3H6O2, CO2 Rank them from highest to lowest percent oxygen by mass. H2O, CO2, C3H6O2, N2O Copyright © Cengage Learning. All rights reserved 6 3 Section 3.7 Determining the Formula of a Compound EXERCISE! The composition of adipic acid is 49.3% C, 6.9% H, and 43.8% O (by mass). The molar mass of the compound is about 146 g/mol. What is the empirical formula? C3H5O2 What is the molecular formula? C6H10O4 Copyright © Cengage Learning. All rights reserved 7 Section 3.9 Balancing Chemical Equations EXERCISE! Which of the following correctly balances the chemical equation given below? There may be more than one correct balanced equation. If a balanced equation is incorrect, explain what is incorrect about it. CaO + C CaC2 + CO2 I. II. III. IV. CaO2 + 3C CaC2 + CO2 2CaO + 5C 2CaC2 + CO2 CaO + (2.5)C CaC2 + (0.5)CO2 4CaO + 10C 4CaC2 + 2CO2 Copyright © Cengage Learning. All rights reserved 4 Section 3.10 Stoichiometric Calculations: Amounts of Reactants and Products EXERCISE! Consider the following reaction: P4(s) + 5 O2(g) 2 P2O5(s) If 6.25 g of phosphorus is burned, what mass of oxygen does it combine with? 8.07 g O2 Copyright © Cengage Learning. All rights reserved 9 Section 3.10 Stoichiometric Calculations: Amounts of Reactants and Products EXERCISE! (Part I) Methane (CH4) reacts with the oxygen in the air to produce carbon dioxide and water. Ammonia (NH3) reacts with the oxygen in the air to produce nitrogen monoxide and water. Write balanced equations for each of these reactions. Copyright © Cengage Learning. All rights reserved 10 5 Section 3.10 Stoichiometric Calculations: Amounts of Reactants and Products EXERCISE! (Part II) Methane (CH4) reacts with the oxygen in the air to produce carbon dioxide and water. Ammonia (NH3) reacts with the oxygen in the air to produce nitrogen monoxide and water. What mass of ammonia would produce the same amount of water as 1.00 g of methane reacting with excess oxygen? Copyright © Cengage Learning. All rights reserved 11 Section 3.11 The Concept of Limiting Reactant EXERCISE! You react 10.0 g of A with 10.0 g of B. What mass of product will be produced given that the molar mass of A is 10.0 g/mol, B is 20.0 g/mol, and C is 25.0 g/mol? They react according to the equation: A + 3B 2C 8.33 g of C is produced Copyright © Cengage Learning. All rights reserved 12 6 Section 3.11 The Concept of Limiting Reactant EXERCISE! Consider the following reaction: P4(s) + 6F2(g) 4PF3(g) What mass of P4 is needed to produce 85.0 g of PF3 if the reaction has a 64.9% yield? 46.1 g P4 Copyright © Cengage Learning. All rights reserved 13 7