Pre-Laboratory exercise: Balance the following reactions: H_2S + MnO_4 rightarro

Question

Pre-Laboratory exercise: Balance the following reactions: H_2S + MnO_4 rightarrow Mn^2+ SO_4^2 (acidic solution) H_2O + MnO_4 + 1 rightarrow IO_3 (basic solution) CN + MnO_4 rightarrow CNO + MnO_2 (basic solution) Br_2 rightarrow BrO_5 + Br (acidic solution) Redox Reactions are the heart of a galvanic or voltaic electrochemical cell. A galvanic or voltaic cell consists of two cell half-reactions separated by salt bridge (consisting of a U-tube usually containing a saturated group I soluble salt, such as potassium chloride with glass wool plugs) connected to an outside circuit.

Explanation / Answer

Q1.

balance acidic

split equations

2H+ + S-2 = SO4-2

MnO4- = Mn+2

balance O

4H2O + 2H+ + S-2 = SO4-2

MnO4- = Mn+2 + 4H2O

balance H+

4H2O + 2H+ + S-2 = SO4-2 + 10H+

8H+ + MnO4- = Mn+2 + 4H2O

balance charge

4H2O + 2H+ + S-2 = SO4-2 + 10H+ + 8e-

5e- + 8H+ + MnO4- = Mn+2 + 4H2O

balance e-

20H2O + 10H+ + 5S-2 = 5SO4-2 + 50H+ + 40e-

8e- + 64H+ + 8MnO4- = 8Mn+2 + 32H2O

add all

8e- + 64H+ + 8MnO4- + 20H2O + 10H+ + 5S-2 = 5SO4-2 + 50H+ + 40e- + 8Mn+2 + 32H2O

cancel common terms

24H+ + 8MnO4- + 5S-2 = 5SO4-2 + 8Mn+2 + 12H2O

this is now balanced in acidic solution

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