Key: These problems are for practice in applying problem solving skills. They ar

Question

Key: These problems are for practice in applying problem solving skills. They are divided by topic, and some are keyed to exercises (see the ends of the exercises). The problems are arranged in matching pairs; the odd-numbered problem each pair is listed first, and its answer is given in the back of the book. Balancing oxidation-Reduction Equations 19.35 Balance the following oxidation reduction equations. The reactions occur in acidic solution. a Cr_2O_7^2- + Cr_2 O_4^2- rightarrow Cr^3+ + CO_3 b. Cu + NO_3^- rightarrow Cu^2+ + NO c. MnO_2 + HNO_2 rightarrow Mn^2+ + NO_3^- d PbO_2 = Mn^2+ SO_4^2- rightarrow PbSO_4 + MnO_4^- e HNO_2 + Cr_2O_7^2- rightarrow Cr^3+ + NO_3^- Balance the following oxidation-reduction equations. The reactions occur in acidic solution. a Mn^2 + + BiO_3^- rightarrow MnO_4^- + Bi^3+ B. Cr_2O_7^2- + I^- rightarrow Cr^3 + IO_3^- c MnO_4^- + H_2SO_3 rightarrow Mn^2+ + SO_4^2- d. Cr_2O_7 + Fe^2+ rightarrow Cr^3+ + Fe^3+ e As + ClO_3^- rightarrow H_3AsO_3 + HClO Balance the following oxidation-reduction equations. The reactions occur in basic solution. a Mn^2+ + H_2O_2 rightarrow MnO_2 + H_2O b. MnO_4^- + NO_2 rightarrow MnO_2 + NO_3^- c. Mn^2 + + ClO_3^- rightarrow MnO_2 + ClO_2 d. MnO_4^- + NO_2 rightarrow MnO_2 + NO_36- Cl_2 rightarrow Cl^- + ClO_3^-, Balance the following oxidation-reduction equations. The reactions occur in basic solution. a Cr(OH)_4^- + H_2O_2 rightarrow CeO_4^2- + H_2O b. MnO_4^- + Br^- rightarrow MnO_2 + BrO_3^- c Co^2+ + H_2O_2 rightarrow Co(OH)_3 + H_2O

Explanation / Answer

Q19.35

For your request,

a)

CrO7-2 + C2O4-2 = Cr+3 + CO2

split metal and Carbon:

CrO7-2 = Cr+3

C2O4-2 = CO2

balance C

CrO7-2 = Cr+3

C2O4-2 = 2CO2

balance O, adding H2O

CrO7-2 = Cr+3 + 7H2O

C2O4-2 = 2CO2

balance H by adding H+

14H+ + CrO7-2 = Cr+3 + 7H2O

C2O4-2 = 2CO2

balance charges adding e-

9e- + 14H+ + CrO7-2 = Cr+3 + 7H2O

C2O4-2 = 2CO2 + 2e-

balane -e

18e- + 28H+ + 2CrO7-2 = 2Cr+3 + 14H2O

9C2O4-2 = 18CO2 + 18e-

add all

9C2O4-2 + 18e- + 28H+ + 2CrO7-2 = 2Cr+3 + 14H2O + 18CO2 + 18e-

cancel common terms

9C2O4-2 +28H+ + 2CrO7-2 = 2Cr+3 + 14H2O + 18CO2

this is now bnalanced in acidic conditions

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