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80 Chapter 4 Chemical Quantities and Aqueous Reactions 2 Au(s) +2 KF(s) Br₂(l) + 2 Oxidation states; 0 +3-1 +1-1 0 +1 +3-1 This is a redox reaction because Au increases in oxidation number (oxidation) and Br decreases in number (reduction). BrF₃ is the oxidizing agent, and Au is the reducing agent. Solution: 24.5 X 1 mol Au 2 = 0.1244 mol KAuF₄ 2 mol 24.5 X 1 X 2 2 mol = 0.1790 mol KAuF 24.5 58.10 1 2 mol 2 mol = 0.4217 mol KAuF₄ 0.1244 mol KAuF₄ X 312.07 g = 38.8 g KAuF₄ 1 mol KAuF₄ Check: The units of the answer (g KAuF₄) are correct. The magnitude of the answer is reasonable compared to the mass of the limiting reactant Au. 4.121 Given: solution may contain Ca²⁺, and Cu²⁺ Find: which ions are present. Conceptual Plan: Test the solution sequentially with NaCl, Na₂SO₄, and Na₂CO₃ and see if precipitates form. Solution: Original solution + NaCl yields no reaction: is not present because chlorides are normally soluble, but Ag+ is an exception. Original solution with Na₂SO₄ yields a precipitate and solution 2. The precipitate is CaSO₄, so Ca²⁺ is present. Sulfates are normally soluble, but Ca²⁺ is an exception. Solution 2 with Na₂CO₃ yields a precipitate. The precipitate is CuCO₃, so Cu²⁺ is present. All carbonates are insoluble. Net Ionic Equations: (aq) + CaSO₄(s) (aq) + CuCO₃(s) Check: The answer is reasonable because two different precipitates formed and all of the Ca²⁺ was removed before the carbonate was added. 4.123 Given: 1.00 g NH₃ Find: g PH₃ Conceptual Plan: Determine reaction sequence, then g mol NH₃ mol PH₃ g PH₃ 1 mol NH₃ 33.99 g PH₃ 17.04 g 1 mol PH₃ Solution: Balance the reaction sequence: 6 + 7 6NO + 9 6 NO + P₄ + 3 N₂ + 6 PH₃ + Therefore, 6 mol NH₃ produces 1 mol PH₃. = Check: The answer is g PH₃, which is correct. The magnitude is reasonable. Even though the molar mass of PH₃ is greater than 6 mol of NH₃ are required to produce 1 mol PH₃. 4.125 Given: 10.0 kg mixture; 30.35% hexane; 15.85% heptane; 53.80% octane Find: total mass CO₂ Conceptual Plan: kg hexane kmol hexane kmol CO₂ kg 1 kmol 12 kmol CO₂ 44.01 kg CO₂ 86.17 kg C₆H₁₄ 2 kmol C₆H₁₄ 1 kmol kg heptane kmol heptane kmol CO₂ kg 1 kmol 7 kmol CO₂ 44.01 kg 100.20 kg C₇H₁₆ 1 kmol C₇H₁₆ 1 kmol kg octane kmol octane kmol CO₂ kg CO₂ 1 kmol C₈H₁₈ 16 kmol CO₂ 44.01 kg CO₂ 114.22 kg C₈H₁₈ 2 kmol C₈H₁₈ 1 kmol CO₂ Copyright © 2017 Pearson Education, Inc.