HalfReactionBalancing

Balance each half reaction adding h and h2o if needed

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Unformatted text preview: -reaction using OH─ ions Balance with CA-WHe, then neutralize H+ Practice Try the last letter on each of these numbers. If easy, go to the next number. Need more practice? Do more. 1. Using the method above, add these half-reactions to get a balanced redox reaction. a. H2 e─ + Ag+ 2 H+ + 2e─ Ag 2C1─ b. 5 e─ + 8H+ + MnO4─ C1 2 + 2e─ Mn2+ + 4 H2O 2. Balance each half-reaction, adding H+ and H2O if needed, then add the half-reactions to get a balanced redox reaction. Ni Ni2+ Cl2 a. Cl─ ©2009 ChemReview.net v. k1 b. Fe3+ NO Fe N O3 ─ Page 388 Module 16: Half-Reaction Balancing c. H2S S MnO4─ d. MnO4─ Mn2+ MnO2 Br─ Br2 3. Balance the result in Problems 2c and 2d using OH─ ions instead of H+. ANSWERS 1a. 2 H+ + 2e─ H2 ─ + 2 Ag+ 2e H2 + 2 Ag+ (multiply all terms in this half-reaction by 2 so e─ balance) 2 Ag 2 H+ + 2 Ag 10 2Cl─ 1b. 10 5 e─ + 16 8H+ + 2 MnO ─ 4 (add terms on same side of arrows; check for balance) 5 Cl + 10 2e─ 2 (To get e─ to balance, multiply by 5) 2 Mn2+ + 8 4 H O 2 (and this one by 2) 10 Cl─ + 2 MnO4─ + 16 H+ 5 Cl2 + 2 Mn2+ + 8 H2O Check: 10 Cl, 2 Mn, 8 O, 16 H atoms on both sides. +4 charge on both sides. Balanced. 2a. Ni2+ + 2 e─ 2 Cl─ Ni 2 e─ + Cl2 (Using CA-WHe, only need e─ to balance charge) (Balance central atom, then add e─ to balance charge) (Since 2 e─ on both sides, half-reactions can be added) Ni2+ + 2 Cl─ Ni + Cl2 Check balance of atoms and charge: 1 Ni, 2 Cl atoms on both sides, neutral on both sides. 2b. Fe3+ + 3 e─ NO + 2 H2O Fe3+ + NO + 2H2O Fe (Using CA-WHe, need only electrons to balance charge) NO3─ + 4 H+ + 3 e─ (Use CA-WHe to balance) ─ (3 e─ on both sides, halves can be added) Fe + NO3 + 4H+ Check: 1 Fe, 1N, 3 O, 4 H atoms on both sides; +3 charge on both sides. Balanced. 2c. H2S 5 e─ + 8 H+ + MnO4─ S + 2H+ + 2 e─ Mn2+ + 4 H O 2 (Use CA-WHe to balance) (Use CA-WHe to balance) Use LCD method to get electrons equal in both: 5H S 2 10 5 e─ + 16 8 H+ + 2 MnO ─ 4 5 H2S + 2 MnO4─ + 6 H+ 5 S + 10 2H+ + 102 e─ 2 Mn2+ + 8 4 H O 2 (5x) (2x) 5 S + 2 Mn2+ + 8 H2O The 16 H+ on the left side of the arrow and the 10 H+ on the right cancel to give 6 H+ on the left. Check: 16 H, 5 S, 2 Mn, 8 O atoms on both sides. Overall +4 charge on both sides. Balanced. ©2009 ChemReview.net v. k1 Page 389 Module 16: Half-Reaction Balancing 2d. 6 3 e─ + 8 4 H+ + 2 MnO4─ 2 MnO2 + 4 2 H2O 3 Br2 + 6 2 e─ 6 2 Br─ 8 H+ + 2 MnO4─ + 6 Br─ (Use CA-WHe to balance, then 2x) (For e─ to balance, multiply by 3) 2 MnO2 + 4 H2O + 3 Br2 Check: 8 H, 2 Mn, 8 O, 6 Br atoms on both sides. Overall zero charge on both sides. Balanced. 3a. 5 H2S + 2 MnO4─ + 6 H+ + 6 OH─ 5 H2S + 2 MnO4─ + 6 H2O 5 S + 2 Mn2+ + 8 H2O + 6 OH─ 5 S + 2 Mn2+ + 2 8 H2O + 6 OH─ Check: 10 H, 5 S, 2 Mn, 8 O atoms on both sides. Overall ─2 charge on both sides. Balanced. 3b. 4 8 H O + 2 MnO ─ + 6 Br─ 2 4 2 MnO2 + 4 H2O + 3 Br2 + 8 OH─ Check: 8 H, 12 O, 2 Mn, 6 Br atoms on both sides. Total ─ 8 charge o...
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