Balancing-Oxidation-Reduction-Reactions-UML：配平氧化還原反應(yīng)的UML-精選課件

1、Balancing Oxidation-Reduction ReactionsAny reaction involving the transfer of electrons is an oxidation-reduction (or redox) reactionBalancing Oxidation-Reduction Definitions:Oxidation is the loss of electrons.Reduction is the gain of electrons.Oxidation cannot take place without reduction.During a

2、redox reaction, the oxidation numbers of reactants will change.Definitions:Oxidation is the lFor any equation to be balanced:1. The number of atoms of each type on the left side of the arrow must equal the number of atoms of each type to the right of the arrow.2. The total charges of all the ions on

3、 the left side of the arrow must equal the total charges of all the ions to the right of the arrow.For any equation to be balanceIn addition, for redox reactions:3. The electrons lost (during oxidation) must equal the electrons gained (during reduction).In addition, for redox reactioBalancing Oxidat

4、ion-Reduction Reactions:1. Assign oxidation numbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions:1. Assign oxidation numbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 Oxygen, in a compound or ion, is

5、 -2Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions:1. Assign oxidation numbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 Use the combined charges of the oxygens in each ion or compound to determine the oxidation number of Cr or C.Balancing Oxidation-Reduction B

6、alancing Oxidation-Reduction Reactions:1. Assign oxidation numbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 -14-8-4Use the combined charges of the oxygens in each ion or compound to determine the oxidation number of Cr or C.Balancing Oxidation-Reduction Balancing Oxidation-Reductio

7、n Reactions:1. Assign oxidation numbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 -14-8-4The sum of the oxidation numbers of the other element must add up to the charge on the ion or molecule.Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions:1. Assign oxidation n

8、umbers to every atom in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 +12-14 +6-8 +3 +4-4The sum of the oxidation numbers of the other element must add up to the charge on the ion or molecule.Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions:1. Assign oxidation numbers to every atom

9、in the reaction. Cr2O72- + C2O42- Cr3+ + CO2 +12 +6 +3 +4Divide the sum of the charges by the number of atoms to get the oxidation number for chromium and carbon in the reactants.Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions:1. Assign oxidation numbers to every atom in the re

10、action. Cr2O72- + C2O42- Cr3+ + CO2 +12/2=+6 +6/2=+3 +3 +4Divide the sum of the charges by the number of atoms to get the oxidation number for chromium and carbon in the reactants.Balancing Oxidation-Reduction Balancing Oxidation-Reduction Reactions: 2. Write bare bones half reactions.Include only t

11、he atom, ion or element that changes oxidation number.Cr+6 + 3e- Cr+3C+3 C+4 + 1e-Remember that each half reaction must also be balanced for charge. The total charges on the left must equal the total charges on the right. Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 3. Take

12、into account any subscripts in the formulas of reactants and products, and multiply the half reactions accordingly.Cr2O72- + C2O42- Cr3+ + CO2 2Cr+6 + 3e- Cr+32C+3 C+4 + 1e- Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 3. Take into account any subscripts in the formulas of r

13、eactants and products, and multiply the half reactions accordingly.Cr2O72- + C2O42- Cr3+ + CO2 2Cr+6 + 6e- 2 Cr+32C+3 2 C+4 + 2e- Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 4. Multiply each half reaction by the appropriate factor so that the number of electrons lost = numb

14、er of electrons gained.12Cr+6 + 6e- 2 Cr+332C+3 2 C+4 + 2e- Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 4. Multiply each half reaction by the appropriate factor so that the number of electrons lost = number of electrons gained. 2Cr+6 + 6e- 2 Cr+3 6C+3 6 C+4 + 6e- Balancing

15、Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 4. Add the two half reactions together. 2Cr+6 + 6e- 2 Cr+3 6C+3 6 C+4 + 6e-2Cr+6 + 6C+3 2 Cr+3 + 6 C+4 Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 4. Add the two half reactions together. 2Cr+6 + 6e- 2 Cr+3 6C+3 6 C

16、+4 + 6e-2Cr+6 + 6C+3 2 Cr+3 + 6 C+4 At this point, the electrons lost = the electrons gained during the reaction. Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 5. You now have the number of each atom that undergoes oxidation or reduction in the balanced equation. Take any sub

17、scripts into account when inserting coefficients.2Cr+6 + 6C+3 2 Cr+3 + 6 C+4 Cr2O72- + 3C2O42- 2Cr3+ + 6CO2 Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 6. Balance the reaction for charge, using OH- (if in base) or H+ (if in acid). The equation below takes place in acid:Cr2O

18、72- + 3C2O42- 2Cr3+ + 6CO2 Charges: -2 + -6 = -8 (left) +6 (right) Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: Cr2O72- + 3C2O42- 2Cr3+ + 6CO2 Charges: -2 + -6 = -8 (left) +6 (right)Since the reaction takes place in acid, you need to add 14 H+ to the left side so that the ch

19、arges become equal. Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 14 H+ + Cr2O72- + 3C2O42- 2Cr3+ + 6CO2 Charges on left = +6 = Charges on right Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 7. Balance for H and O by adding water to the appropriate sid

20、e of the reaction.14 H+ + Cr2O72- + 3C2O42- 2Cr3+ + 6CO2 + 7 H2O Balancing Oxidation-Reductio Balancing Oxidation-Reduction Reactions: 8. Check the balance for all atoms in the reaction.14 H+ + Cr2O72- + 3C2O42- 2Cr3+ + 6CO2 + 7 H2OLeft: 14 HRight: 14 H 2 Cr 2 Cr19 O19 O 6 C 6 C Balancing Oxidation-ReductioRedox StoichiometryCalculations involving concentrations and redox reactions are quite common. Many ores containing metals are analyzed using redox titrations. Since many compounds change color as they are oxidized or reduced, one of the