HalfReactionBalancing

Method 4 h 2 e pbo2 mno 3 h2o pb2 2 h2o 5 e 6 h

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Unformatted text preview: 2 KMnO4 + 6 HNO3 + 5 H2O2 2 Mn(NO3)2 + 5 O2 + ___ KNO3 + 8 H2O Final: 2 KMnO4 + 6 HNO3 + 5 H2O2 2 Mn(NO3)2 + 5 O2 + 2 KNO3 + 8 H2O Step 8: 2 K, 2 Mn, 36 O, 16 H, 6 N atoms on both sides, zero net charge on both sides. Balanced. 3. MnO + PbO2 + HCl HMnO4 + PbC12 + H2O Steps 1 and 2: Break compounds that ionize into separated ions, then cross out the spectators and particles that are the same on both sides: Strong acids ionize 100% in water. H+ + MnO4─ + Pb2+ + 2 C1─ + H2O MnO + PbO2 + H+ + Cl─ Step 3: Find the 2 atoms that change their oxidation number. Each +2 -2 + 4 -2 MnO + PbO2 +7 -2 +2 +1 -2 ─ + Pb2+ + H O MnO4 2 Steps 4 and 5: Write the 4 particles containing the 2 atoms that change their oxidation number in separate half-reactions, then balance the half-reactions using the CA-WHe! method. 4 H+ + 2 e─ + PbO2 MnO + 3 H2O Pb2+ + 2 H2O 5 e─ + 6 H+ + MnO4─ Step 6: Get electrons equal in both, then add the half-reactions. 20 4 H+ + 10 2 e─ + 5 PbO 2 2 MnO + 6 3 H O 2 2 MnO + 8 H+ + 5 PbO2 5 Pb2+ + 10 2 H O 2 10 5 e─ + 12 6 H+ + 2 MnO ─ 4 (5x) (2x) 5 Pb2+ + 2 MnO4─ + 4 H2O Check: 2 Mn, 12 O, 8 H, 5 Pb atoms on both sides, +8 charge on both sides. Balanced. Step 7: Plug trial coefficients into the original equation; finish balancing by trial and error. 2 MnO + 5 PbO2 + 10 8 HCl 2 HMnO4 + 5 PbC12 + 4 H2O Step 8: Check: 2 Mn, 12 O, 10 H, 5 Pb, 10 Cl atoms, zero charge on both sides. Balanced. The HCl coefficient must be adjusted to balance the spectators, but the balanced half-reactions get you close to the final answer. 4. In problem 1, the half-reactions show Cu losing electrons in the reaction. That means Cu is being oxidized. In problem 2, the half reactions show the reactant H2O2 losing electrons -- being oxidized. In problem 3, the half reactions show the reactant MnO losing electrons -- being oxidized. ***** ©2009 ChemReview.net v. k1 Page 397 Module 16: Half-Reaction Balancing Lesson 16E: Review Quiz For Modules 13-16 You may use a calculator and a periodic table. Work on your own paper. Set a 35-minute limit, then check your answers after the Summary that follows. ***** 1. Label each of these compounds as soluble or insoluble in water. a. (NH4)3PO4 2. For the reaction b. AgBr Pb(NO3)2 + c. Pb(NO3)2 d. BaCO3 e. CaCl2 KCl a. Write a total ionic equation. b. Write the net ionic equation. 3. In the reaction in Problem 2, if 0.100 L of Pb(NO3)2 solution is reacted with excess KCl, and the weight of the rinsed and dried solid product is 11.12 g, what was the original [Pb(NO3)2]? 4. If 912 mg of a dry solid acid is neutralized by 22.0 mL of 0.120 M NaOH, assuming that each acid particle contains two acidic hydrogens, a. How many moles of acid were in the acid sample? b. What is the molar mass of the unknown acid? 5. Write the final products in molecular (solid) formulas and balance this equation. Assume the reaction goes to completion. CH3COOH + KHCO3 6. Balance: FeCl2 + KMnO4 + HCl MnCl2 + FeCl3 + H2O + KCl 7. In problem 6, which substance is the red...
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