Question

a Choose the balanced equation for the following half-reaction, which takes place in acidic solution MnO4 (aq)Se2 (aq) -> Mn2(aq) Se(s) O 16H (aq)2Mn04- (aq)5Se2 (aq) ->2Mn2 (aq) 6H20()5Se(s) O16H (aq)2MnO4- (aq)5Se2 (aq) -2Mn2 (aq) 8H20(1) 5Se(s) 16H+ (aq)MnO4 (aq) 5Se2(aq) - Mn2(aq) +8H20(l) 5Se(s) O16H (aq)MnO4- (aq) 5Se2 (aq) -2Mn2(aq) + 8H2O(l)5Se(s) bChoose the balanced equation for the following half-reaction, which takes place in acidic solution: S2Os2(aq)CI (aq) SO42(aq) Cl2 (aq) S2O82(aq)2CI (aq) 2SO42(aq) Cl2(aq) S2O82-(aq)C (aq) -2SO42-(aq) 2Cl2 (aq) 2S2032 (aq)2Cl (aq)4SO42- (aq) 2C12 (aq) S2O82-(aq)2CI (aq) 2SO42-(aq)2Cl2(aq)

Answer 1

a)

Mn in MnO4- has oxidation state of +7

Mn in Mn+2 has oxidation state of +2

So, Mn in MnO4- is reduced to Mn+2

Se in Se-2 has oxidation state of -2

Se in Se has oxidation state of 0

So, Se in Se-2 is oxidised to Se

Reduction half cell:

MnO4- + 5e- --> Mn+2

Oxidation half cell:

Se-2 --> Se + 2e-

Balance number of electrons to be same in both half reactions

Reduction half cell:

2 MnO4- + 10e- --> 2 Mn+2

Oxidation half cell:

5 Se-2 --> 5 Se + 10e-

Lets combine both the reactions.

2 MnO4- + 5 Se-2 --> 2 Mn+2 + 5 Se

Balance Oxygen by adding water

2 MnO4- + 5 Se-2 --> 2 Mn+2 + 5 Se + 8 H2O

Balance Hydrogen by adding H+

2 MnO4- + 5 Se-2 + 16 H+ --> 2 Mn+2 + 5 Se + 8 H2O

This is balanced chemical equation in acidic medium

Answer: option 2

b)

S in S2O8-2 has oxidation state of +7

S in SO4-2 has oxidation state of +6

So, S in S2O8-2 is reduced to SO4-2

Cl in Cl- has oxidation state of -1

Cl in Cl2 has oxidation state of 0

So, Cl in Cl- is oxidised to Cl2

Reduction half cell:

S2O8-2 + 2e- --> 2 SO4-2

Oxidation half cell:

2 Cl- --> Cl2 + 2e-

Number of electrons is same in both half reactions.

So, balancing of electrons is not required. It's already balanced

Lets combine both the reactions.

S2O8-2 + 2 Cl- --> 2 SO4-2 + Cl2

Balance Oxygen by adding water

Oxygen is already balanced

Hydrogen is already balanced

S2O8-2 + 2 Cl- --> 2 SO4-2 + Cl2

This is balanced chemical equation in basic medium

Answer: OPTION 1