01 Redox

Question 1

Oxidation, [O]

Answer 1

1. Gain of Oxygen, O
2. Loss of Hydrogen, H.
3. Loss of electron(s) (e^-)
4. Increase in Oxidation Number (ON)

Question 2

Reduction, [R]

Answer 2

1. Loss of Oxygen, O
2. Gain of Hydrogen, H.
3. Gain of electron(s) (e^-)
4. Decrease in Oxidation Number (ON)

Question 3

Assigning O.N

Rules

Answer 3

1. ON of atoms in elemental state = 0
2. ON of H in all compounds except metal hydrides (M-H) = +1
   a. ON of H in M-H = -1
3. ON of O in all compounds except peroxides (O₂^2-, superoxides (O₂^-) and OF₂ = -2.
   a. ON of O in O₂^2- = -1
   b. ON of O in O₂^- = -1/2
   c. ON of O in OF₂ = +2
4. ON of F in all compounds = -1
5. More electronegative, EN, atom has the negative ON and vice versa.
6. In monoatomic ions, ON = charge of ion.
7. In polyatomic ions, sum of ON = charge of ion.
8. In a compound, sum of ON of atoms = 0

Question 4

Balancing Equations

in Acidic Medium

Answer 4

1. Construct the oxidation/ reduction half-equation.
2. Balance all elements except H and O.
3. Balance O atoms by adding H₂O.
4. Balance H atoms by adding H⁺.
5. Balance overall charge by adding e^-.
6. Balance e^- gained and e^- lost by multiplying each balanced half-equation appropriately.
7. Add the half-equations and cancel out common terms to obtain the balanced half-equation.

For step 5, [O] have e^- on RHS, [R] have e^- on LHS

Question 5

Balancing Equations

in Basic Medium

Answer 5

1. Obtain half-equations in Acidic Medium using step 1-5.
   a. “Neutralise” H+ by adding the same number of OH- to both sides of half-equation.
   b. Combine H+ and OH- on the same side of the equation to form H2O.
   c. Re-balance half-equation.
2. Combine balanced half-equations to obtain overall balanced equation using step 6-7.