HalfReactionBalancing

Neutralize the h by adding oh to both sides 3 react

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: + 14 H+ + Cr2O72─ 2 Cr3+ + 7 H2O 2. Neutralize the H+ by adding OH─ to both sides. 6 e─ + 14 H+ + Cr2O72─ + 14 OH─ 2 Cr3+ + 7 H2O + 14 OH─ 3. React the H+ and OH─ to form H2O. 6 e─ + 14 H2O + Cr2O72─ 2 Cr3+ + 7 H2O + 14 OH─ 4. Adjust the count of the H2O. 7 H2O cancel on both sides. 6 e─ + 14 H2O + Cr2O72─ 7 2 Cr3+ + 7 H2O + 14 OH─ 5. Check: 14 H, 2 Cr, 14 O, 8 negative charges on both sides. Practice C Do every other problem. Save the rest for your next practice session. 1. Modify these half-reactions to balance using OH─ ions instead H+. a. 3 e─ + NO3─ + 4 H+ b. H2O2 2 H+ + O2 NO + 2 H2O + 2 e─ 2. Balance these half-reactions using OH─ and H2O. a. Cr3+ ©2009 ChemReview.net v. k1 CrO42─ Page 384 Module 16: Half-Reaction Balancing b. MnO4─ MnO2 c. C2H4O C2H6O ANSWERS Pretest 2. 2e─ + F2 1. The gain of electrons. 2 F─ 4a. Sn4+ (OA) + Co (RA) 3. Cl = +5, Mn = +7 Ca (RA) + 2 H+ (OA) 4b. Practice A The total of the charges on both sides must balance. 1a. 3 e─ + NO3─ + 4 H+ NO + 2 H2O 1b. H2O2 2 H+ + O2 + 2 e─ 2a. 2 e─ + SO42─ + 4 H+ SO2 + 2 H2O 2b. 8 H2S S8 + 16 H+ + 16 e─ 2c. MnO2 + 4 H+ + 2 e─ Mn2+ + 2 H2O 2d. 1 NH4+ + 3 H2O 1 NO3─ + 10 H+ + 8 e─ Practice B 1. First balance the Central Atom: 2 ClO3─ Then WHe: Add water to balance O: H+ to balance H: 2 ClO3─ 2 ClO3─ + 12 H+ e─ to balance charge: Cl2 Cl2 + 6 H2O Cl2 + 6 H2O 2 ClO3─ + 12 H+ + 10 e─ Cl2 + 6 H2O Check: 2 Cl, 6 O, 12 H, zero charge on both sides. Balanced. 2. Central atom, O, and H are already balanced. Use e─ to balance charge. Pb + SO 2─ PbSO + 2 e─ 4 4 Check: 1 Pb, 1 S, 4 O, 2 negative charges on both sides. Balanced. 3. Central atom S is balanced. Use water to balance O: SO2 + 2 H2O SO42─ 4H+ + SO42─ Use e─ to balance charge: SO2 + 2 H2O 2 e─ + 4H+ + SO42─ Use H+ to balance H: SO2 + 2 H2O Check: 1 S, 4 O, 4 H, zero charge on both sides. Balanced. 4. MnO4─ + 4 H+ + 3 e 6. Au Au3+ + 3 e─ ©2009 ChemReview.net v. k1 MnO2 + 2 H2O 7. 2 H2O 5. Br2 + 8 H2O 2 BrO4─ + 16 H+ + 14 e─ O2 + 4 H+ + 4 e─ Page 385 Module 16: Half-Reaction Balancing Practice C 1a. Add enough OH─ to both sides to neutralize H+. NO + 2 H2O + 4 OH─ 3 e─ + NO3─ + 4 H+ 4 H2O NO + 2 H2O + 4 OH─ Adjust the H2O 3 e─ + NO3─ + 2 4 H2O NO + 4 OH─ Final. 3 e─ + NO ─ + 2 H O 3 2 Check: 1 N, 5 O, 4H, 4 negative charges on both sides. Balanced. 1b. 2 OH─ + H2O2 2 H+ + O2 + 2 e─ 2 H2O Final: 2 OH─ + H2O2 2 H2O + O2 + 2 e─ Check: 4 O, 4 H, 2 negative charges on both sides. Balanced. 2a. First balance using CA-WHe! method. CrO42─ + 8 H+ + 3 e─ 4 H2O + Cr3+ Then add enough OH─ to both sides to neutralize H+. 8 OH─ + 4 H2O + Cr3+ CrO42─ + 8 H+ + 3 e─ 8 H2O Then adjust the water. 8 OH─ + 4 H2O + Cr3+ Final: 8 OH─ + Cr3+ CrO42─ + 4 8 H2O + 3 e─ CrO42─ + 4 H2O + 3 e─ Check: 8 O, 8 H, 1 Cr, 5 negative charges on both sides. Balanced. 2b. Balance using CA-WHe first: 3 e─ + 4 H+ + MnO4─ Neutralize the H+: 3 e─ + 4 H+ + 4 H2O + MnO4─ Adjust the H2O: 3 e─ + 2 4 H2O + MnO4─ MnO2 + 2 H2O MnO2 + 2 H2O + 4 OH─ MnO2 + 2 H2O + 4 OH─ Check: 4 H, 6 O, 1 Mn, 4 n...
View Full Document

This note was uploaded on 10/28/2010 for the course CHAP 12 taught by Professor Lebec during the Spring '10 term at Marlboro.

Ask a homework question - tutors are online