Question

Balance redox reactions in basic solution. Balance the reaction between SO42- and Br- to form SO32- and Br2 in basic solution. When you have balanced the equation using the smallest integers possible, enter the coefficients of the species shown. Enter "1" if the coefficient is "1". SO42- + Br-SO32- + Br2 Water appears in the balanced equation as a _____(reactant, product, neither) with a coefficient of . (Enter 0 for neither.) How many electrons are transferred in this reaction?

Answer 1

S in SO4-2 has oxidation state of +6
S in SO3-2 has oxidation state of +4
So, S in SO4-2 is reduced to SO3-2

Br in Br- has oxidation state of -1
Br in Br2 has oxidation state of 0
So, Br in Br- is oxidised to Br2





Reduction half cell:
SO4-2 + 2e- --> SO3-2
Oxidation half cell:
2 Br- --> Br2 + 2e-
Number of electrons is same in both half reactions.
So, balancing of electrons is not required. It's already balanced

2 electrons are being transferred

Lets combine both the reactions.
SO4-2 + 2 Br- --> SO3-2 + Br2
Balance Oxygen by adding water

SO4-2 + 2 Br- --> SO3-2 + Br2 + H2O

Balance Hydrogen by adding H+
SO4-2 + 2 Br- + 2 H+ --> SO3-2 + Br2 + H2O

Add equal number of OH- on both sides as the number of H+
SO4-2 + 2 Br- + 2 H+ + 2 OH- --> SO3-2 + Br2 + H2O + 2 OH-

Combine H+ and OH- to form water
SO4-2 + 2 Br- + 2 H2O --> SO3-2 + Br2 + H2O + 2 OH-

Remove common H2O from both sides
Balanced Eqn is
SO4-2 + 2 Br- + H2O --> SO3-2 + Br2 + 2 OH-
This is balanced chemical equation in basic medium

Answer:
1, 2, 1, 1
Water appear as a reactant with coefficient of 1
2 electrons are being transferred