Redox (Half-equations)

Question 1

Half Equation

Answer 1

Shows a substance being:

Oxidised ~ electrons on RHS

             OR

Reduce ~ electrons on LHS

Question 2

REDUCTION half equation

Answer 2

• electrons on the LEFT
• oxidising agent

Br2 + 2e- ——- 2Br-

Question 3

OXIDATION half equation

Answer 3

• electrons on the RIGHT
• reducing agent

Cu —- Cu2+ + 2e-

Question 4

Writing half equations

Answer 4

• write the reagent & product either side of arrow
• Balance the atoms on either side
• Add WATER molecules to balance OXYGEN atoms
• Add H+ ions to balance HYDROGEN atoms
• Add ELECTRONS to balance the change in oxidation number

Question 5

Constructing REDOX equations using oxidation numbers (ACIDIC)

Answer 5

• Find the OXIDATION NUMBER of each element in the reactants & products
• identify which element is being oxidised & reduced
• Balance the increase & decrease of oxidation numbers
• Check equation is balanced & has lowest possible ratios

Question 6

Constructing REDOX equations using oxidation numbers (ALKALINE) 1

Answer 6

• Find the OXIDATION NUMBER of each element in the reactants & products
• identify which element is being oxidised & reduced
• Balance the increase & decrease of oxidation numbers
• Add extra OH- ions to the LHS to balance OXYGEN atoms
• Add further OH- ions on the LHS
• Balance the WATER

Question 7

Constructing REDOX equations using oxidation numbers (ALKALINE) 2

Answer 7

When balancing the equations with OH- & H2O:

• add 2x the number of OH- ions on the LHS
• this balances the oxygen atoms on the RHS

The same number of water molecules will be formed as the number of oxygen atoms added on the left via OH- ions