redox 3 and 14

In an ionic compound, how do you determine the oxidation states of elements?

The metal has a positive oxidation state, and the non-metal has a negative oxidation state.

In a covalent molecule, which atom has the negative oxidation state?

The more electronegative atom.

What is the balanced half-equation for the reduction of NO₃⁻ to NO in acidic conditions?

NO₃⁻ + 4H⁺ + 3e⁻ → NO + 2H₂O

What do electrochemical cells produce from redox reactions?

An electric potential difference.

What completes the circuit in an electrochemical cell?

A salt bridge.

Why is potassium nitrate used in salt bridges?

Because it does not react to form precipitates with ions in the half-cells.

What is the general format for cell notation?

Reduced | Oxidised || Oxidised | Reduced

What is used as the reference electrode in measuring standard electrode potentials?

The standard hydrogen electrode.

Why is platinum used in some electrode systems?

It is unreactive and conducts electricity.

Why might a silver/silver chloride electrode be used instead of a hydrogen electrode?

It is easier to set up and maintain.

What is the formula for calculating E⦵ cell?

E⦵cell = E⦵ (right-hand electrode) - E⦵ (left-hand electrode)

What is a key requirement for a reaction to be thermodynamically feasible?

E⦵cell must be positive.

Why might a reaction with a positive E⦵cell not occur?

Due to high activation energy or non-standard conditions.

What makes a storage cell rechargeable

The chemical reaction is reversible.

What are the electrodes in a lead-acid cell?

Negative: Pb; Positive: PbO₂

Why is lithium used in lithium cells?

It is light and reactive, producing a large emf.

How are lithium electrodes made safe?

Lithium is inserted into crystal lattices and uses non-aqueous electrolytes.

How do fuel cells differ from regular electrochemical cells?

They have a continuous supply of reactants and produce a steady current.

What are the half-reactions in a hydrogen fuel cell under acidic conditions?

• H₂ → 2H⁺ + 2e⁻

• ½O₂ + 2H⁺ + 2e⁻ → H₂O

What are the half-reactions in alkaline conditions?

• 2H₂O + 2e⁻ → H₂ + 2OH⁻

• ½O₂ + H₂O + 2e⁻ → 2OH⁻

What fuel can be used instead of hydrogen in biofuel cells?

Methanol (CH₃OH).

CH3OH + H2O → CO2 + 6H+ + 6e-.

3/2O2 + 6H+ + 6e- → 3H2O

Why is KMnO₄ used in redox titrations?

It is a stable oxidising agent and acts as its own indicator.

What is the ionic equation for MnO₄⁻ in acidic solution?

MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O

Why is starch used in iodine/thiosulphate titrations?

It forms a blue complex with iodine, disappearing when all iodine is reduced.

What is the equation for iodine being reduced?

I₂ + 2e⁻ → 2I⁻

What is the thiosulphate oxidation half-equation?

2S₂O₃²⁻ → S₄O₆²⁻ + 2e⁻