Redox Reaction

Question 1

Oxidation VS reduction

Answer 1

O: gain in O2, loss of H2, loss of e, increase in O.N
R: loss of O2, gain in H2, gain in e, decrease in O.N.

Question 2

DISPROPORTION

Answer 2

• A redox reaction in which oxidation and reduction of an atom of the same element in the species occurs simultaneously.

Question 3

OXIDATION NUMBER

Answer 3

• The oxidation of an atom signifies the number of charges the atom would have in a molecule (or ionic compound) if electrons were completely transferred.
  
  • +/- signs must be stated before the number

Question 4

Some rules for O.N.

Answer 4

1. atoms of elements in their most natural state
   = 0
2. monoatomic ion = charge of ion
3. neutral molecule or compound = overall charge of all atoms must be 0
4. Polyatomic ion = sum of overall charge must be equal to the net charge of ion

Question 5

ELECTRONEGATIVITY

Answer 5

• The ability of an atom to attract electrons in a covalent bond towards itself
  
  • Electronegativity
    ○ Increases across the period
    ○ Decreases down the group
  • More electronegative atom –> negative O.N.
  • Less electronegative atom –> positive O.N.

Question 6

STEPS in acidic medium

Answer 6

• In acidic medium:
  (1) Identify the oxidation and reduction half-equations
  (2) Balance both the half-equations using the following steps:
  ○ Balance the atoms undergoing oxidation/reduction
  ○ Balance oxygen atoms by adding H2O to the side with fewer oxygen
  ○ Balance hydrogen atoms by adding H+ to the side with fewer hydrogen
  ○ Balance charges by adding electrons to the side with more positive charge (since electrons are negatively charged)
  (3) Multiply the balanced half-equations by appropriate integers such that the number of electrons in both half-equations are equal.
  (4) Add the resulting half-equations together, and eliminate any common species on both sides to obtain overall balanced equation.
  (King On High Chair)

Question 7

STEPS in alkaline medium

Answer 7

• In acidic medium:
  (1) Identify the oxidation and reduction half-equations
  (2) Balance both the half-equations using the following steps:
  ○ Balance the atoms undergoing oxidation/reduction
  ○ Balance oxygen atoms by adding H2O to the side with fewer oxygen
  ○ Balance hydrogen atoms by adding H+ to the side with fewer hydrogen
  ○ Balance charges by adding electrons to the side with more positive charge (since electrons are negatively charged)
  (3) Multiply the balanced half-equations by appropriate integers such that the number of electrons in both half-equations are equal.
  (4) Add the resulting half-equations together, and eliminate any common species on both sides to obtain overall balanced equation.
  (5) Add OH- to both sides of the equation such that any H+ present will be neutralised to form water i.e. H+ + OH- –> H2O
  (6) Eliminate any common H2O molecules on both sides of the equation