Balancing Redox Equations in Acidic or Basic Solutions In addition to mass balan

Question

Balancing Redox Equations in Acidic or Basic Solutions

In addition to mass balance, oxidation-reduction reactions must be balanced such that the number of electrons lost in the oxidation equals the number of electrons gained in the reduction. This balancing can be done by two methods. The oxidation number method balances the net increase in oxidation of the substance oxidized with the net decrease in the oxidation number of the substance reduced. The half-reaction method balances the electrons lost in the oxidation half-reaction with the electrons gained in the reduction half-reaction. In both methods

H2O(l),OH?(aq), and H+ (aq) may be added to complete the mass balance. Which substances are used depends on the reaction conditions.

Acidic solution

In acidic solution, bromate ion can be used to react with a number of metal ions. One such reaction is

BrO3?(aq)+Sn2+(aq)?Br?(aq)+Sn4+(aq)

Since this reaction takes place in acidic solution,

H2O(l)andH+(aq) will be involved in the reaction. Places for these species are indicated by the blanks in the following restatement of the equation:

BrO3?(aq)+Sn2+(aq)+ ____ ?Br?(aq)+Sn4+(aq)+ ___

Part A

What are the coefficients of the six species in the balanced equation above? Remember to include coefficients for

H2O(l)andH+(aq)

in the appropriate blanks.

Enter the equation coefficients in order separated by commas (e.g., 2,2,1,4,4,3).

Basic solution

Potassium permanganate,

KMnO4, is a powerful oxidizing agent. The products of a given redox reaction with the permanganate ion depend on the reaction conditions used. In basic solution, the following equation represents the reaction of this ion with a solution containing sodium sulfite:

MnO4?(aq)+SO32?(aq)?MnO2(s)+SO42?(aq)Since this reaction takes place in basic solution,H2O(l)andOH?(aq)

will be shown in the reaction. Places for these species are indicated by the blanks in the following restatement of the equation:

MnO4?(aq)+SO32?(aq)+ ____?MnO2(s)+SO42?(aq)+ ___

Part B

What are the coefficients of the six species in the balanced equation above? Remember to include coefficients for

H2O(l)andOH? (aq) in the blanks where appropriate.

Enter the equation coefficients in order separated by commas (e.g., 2,2,1,4,4,3).

Explanation / Answer

Part A

6e- + 6H+ + BrO3 - --> Br - + 3H2O

(Sn+2--> Sn +4 + 2e- ) x 3

________________________

BrO3- + 3Sn+2 + 6H+ ----> Br - + 3 Sn+4 + 3H2O

Coefficients: 1,3,6,1,3,3

Part B)

4e- + 4H+ + MnO4 ----> MnO2  + 2H2O

(H2O + SO3-2 -----> SO4-2 + 2H+ + 2e- ) x 2

__________________________________________

MnO4 + 2SO3-2 ---> MnO2 + 2SO4-2

Coefficients: 1,2,0,1,2,0

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