Question

balancing basic reactions

S₂O₈^2- (aq) +    Ni (OH)₂ (s) ------> SO₄ ^2- (aq) + NiO₂ (s)

Answer 1

Step 1: Separate the half-reactions.

S₂O₈^2- (aq) ------> SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s)

Step 2: Balance elements other than O and H. We have two sulfur atoms on the left side and one on the right side. The Ni atom is already balanced.

S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s)

Step 3: Add H₂O to balance oxygen. In our reaction, the oxygen atom is already balanced. So, there is no change in this step.

S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO² (s)

Step 4: Balance hydrogen by adding protons (H⁺). In the first reaction there is no H atom. In the second part, we need add two protons to balance the hydrogen atoms.

S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s) + 2H⁺

Step 5: Balance the charge of each equation with electrons. To balance, the charges on the first reaction we need to add 2 e^-'s on the left side of the reaction.
For the second part of the reaction, to balance the charge we need to add 2e^- on the right side.

2e- + S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s) + 2H⁺ + 2e^-

Step 6: Scale the reactions so that the electrons are equal. Since, the electrons are already balanced, we don't need to scale the reaction parts.

2e- + S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s) + 2H⁺ + 2e-

Step 7: Add the reactions and cancel out common terms.

2e- + S₂O₈^2- (aq) ------> 2SO₄^2- (aq)
Ni(OH)₂ (s) ------> NiO₂ (s) + 2H₊ + 2e-

--------------------------------------------

2e- + S₂O₈^2- (aq) + Ni(OH)₂ (s) ------> 2SO₄^2- (aq) + NiO₂ (s) + 2H⁺ + 2e-

S₂O₈^2- (aq) + Ni(OH)₂ (s) ------> 2SO₄^2- (aq) + NiO₂ (s) + 2H⁺

therefore, the balanced net reaction is:

S₂O₈^2- (aq) + Ni(OH)₂ (s) ------> 2SO₄^2- (aq) + NiO₂ (s) + 2H⁺