Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Balancing Redox Equations 0 0 +2 -2 Analyze Mg + S MgS • • 1. 2. What is oxidized? What is reduced? Assign Oxidation Numbers. Figure out change in oxidation numbers. Mg goes from 0 to +2: Oxidation S goes from 0 to -2: Reduction 2 electrons Mg + S MgS 2 electrons 3. Identify what species is oxidized & what species is reduced. 4. Figure out the 2 half-reactions. Half-Reactions 0 0 +2 -2 Mg + S MgS Mg is oxidized: S is reduced: Mg Mg+2 + 2e- S + 2e- S-2 5. Adjust half-reactions so electrons lost = electrons gained. 6. Add half-reactions. Mg Mg+2 + 2e- S-2 S + 2e __________________________________ Mg + S + 2e- Mg+2 +2e- + S-2 7. Balance everything else by counting atoms. 0 +1 -1 0 +2 -1 Zn + HCl H2 + ZnCl2 • Zn goes from 0 to +2: oxidation. • H goes from +1 to 0: reduction. • Cl goes from -1 to -1: No change. 2 electrons Zn + HCl H2 + ZnCl2 1 electron per H Zn Zn+2 + 2e+1 + 2e- H 2H 2 ______________________________________ Zn + +1 2H +2e +2 Zn +2e + H2 Transfer the coefficients! Zn + 2H+1 H2 + Zn+2 • This is what you’ve got from adding the 2 half-reactions. Zn + HCl H2 + ZnCl2 • This is the skeleton equation you started with. • Transfer the coefficients. Zn + 2HCl H2 + ZnCl2 Balancing Redox Equations 1. Assign oxidation numbers to all atoms in equation. 2. See which elements have changes in oxidation number. 3. Identify atoms that are oxidized & atoms that are reduced. 4. Write the half-reactions. Diatomics have to be written as diatomics. 5. Make the number of electrons lost & gained equal in magnitude by multiplying half-reactions as needed. 6. Add the half-reactions. Transfer coefficients to skeleton equation. 7. Balance remainder of equation by counting up atoms. 0 +1 +5 -2 +2 +5 -2 0 Cu + AgNO3 Cu(NO3)2 + Ag • • • • Cu goes from 0 to +2: oxidation. Ag goes from +1 to 0: reduction. N goes from +5 to +5: No change. O goes from -2 to -2: No change. Half-Reactions Multiply by 2 Cu Cu+2 + 2eAg+1 + 1e- Ag Cu Cu+2 + 2e+1 + 2e- 2Ag 2Ag ______________________ Cu + 2Ag+1 + 2e- 2Ag + Cu+2 + 2e- Transfer Coefficients • Compare skeleton equation & sum of halfreactions: Cu + AgNO3 Ag + Cu(NO3)2 Vs. Cu + 2Ag+1 + 2e- 2Ag + Cu+2 + 2e• Transfer the coefficients! Cu + 2AgNO3 2Ag + Cu(NO3)2) Exception: Do NOT insert the coefficient of any item that appears in more than one place in the equation. 0 +1 +5 -2 +2 +5 -2 +4 -2 +1 -2 Cu + HNO3 Cu(NO3)2 + NO2 + H2O 1. Assign Oxidation Numbers. 2. Identify which species are oxidized & which reduced. Cu from 0 to +2 = oxidized H from +1 to +1 so no change O from -2 to -2 so no change N all starts as +5. Some ends as +5, some as +4 = reduction Change of +2 Cu + HNO3 Cu(NO3)2 + NO2 + H2O 2 2 2(Change of -1 ) = -2 3. Find change in oxidation number. 4. Write half-reactions. Cu Cu+2 + 2eN+5 + 1e- N+4 What’s oxidized? What’s reduced? • What is oxidized? Cu • What is reduced? Can’t just say N. It’s the N in the HNO3. Or the HNO3 or N+5. • What is the oxidizing agent? • What is the reducing agent? N+5 Cu 5. Multiply half-reactions as necessary. Cu Cu+2 + 2e2N+5 + 2e- 2N+4 • Now the # of electrons lost = # gained. 6. Add half-reactions. Transfer coefficients. Cu + 2HNO3 Cu(NO3)2 + 2NO2 + H2O 7. Balance remaining atoms by inspection. Cu + 4HNO3 Cu(NO3)2 + 2NO2 + 2H2O