Half equations - DM

Question 1

What are the only things you can add to a half equation

Answer 1

H⁺, H₂O, e⁻

Question 2

What is the order when balancing half equations

Answer 2

balance other atoms first (not H or O), add H₂O, then H⁺ and finally e⁻

Question 3

How to add half equations

Answer 3

one must be reduction and the other oxidation.
1. both must have the same number of electrons (multiply as needed).
2. write all reactants and all products together.
3. cancel where possible

Question 4

Steps in adding Cu²⁺ + 2e⁻ -> Cu and Ag -> Ag⁺ + e⁻

Answer 4

1. both must have the same number of electrons
   Ag -> Ag⁺ + e⁻ x2
   = 2Ag -> 2Ag⁺ + 2e⁻
2. write all reactants and all products together.
   Cu²⁺ + 2e⁻ + 2Ag -> Cu + 2Ag⁺ + 2e⁻
3. cancel where possible
   Cu²⁺ + 2Ag -> Cu + 2Ag⁺

Question 5

What are the 2 ways in balancing an unbalanced redox equation

Answer 5

• use oxidation states
• pull out half equations, balance, add back together

Question 6

Steps to balancing the unbalanced redox equation: Re³⁺ + H₂O + MnO₄³⁻ -> Mn²⁺ + ReO₄²⁻ + H⁺

Answer 6

1. pull out the half equations and balance
   Re³⁺ -> ReO₄²⁻ (balance)
   Re³⁺ + 4H₂O -> ReO₄²⁻ + 8H⁺ + 3e⁻
   MnO₄⁻ -> Mn²⁺
   MnO₄⁻ + 8H⁺ + 5e⁻ -> Mn²⁺ + 4H₂O
2. multiply if necessary
   5Re³⁺ + 20H₂O -> 5ReO₄²⁻ + 40H⁺ + 15e⁻
   3MnO₄⁻ + 24H⁺ + 15e⁻ -> 3Mn²⁺ + 12H₂O
3. add back together
   5Re³⁺ + 20H₂O + 3MnO₄⁻ + 24H⁺ + 15e⁻ -> 5ReO₄²⁻ + 40H⁺ + 15e⁻ + 3Mn²⁺ + 12H₂O
4. cancel
   5Re³⁺ + 8H₂O + 3MnO₄⁻ -> 5ReO₄²⁻ + 16H⁺ + 3Mn²⁺