Question

List 4 common reference electrodes; describe their advantages, limitations and how to convert their values to the Normal Hydrogen Electrode (NHE) potential.

Answer 1

A reference electrode is an electrode which has a known electrode potential and is stable, used to determine the half cell potentials of unknown electrodes. Some of the most common reference electrodes include

1. Standard hydrogen electrode 2. Calomel electrode 3. Silver-silver chloride electrode 4. Copper copper sulfate electrode

1. sHE: The hydrogen gas is bubbled at a platinum electrode trade in an aquous solution containing H+ ions.

H₂(g) → 2H⁺(aq) + 2e^- (oxidation) ( If SHE is used as anode)

2H⁺ + 2e H_{2 (reduction)} ( if SHE is used as cathode)

Advantages of SHE: 1 It has a zero potential, hence its correction is not needed.

2 It can be used over entire pH range and gives no salt error.

Disadvantages. : it is difficult to produce dry hydrogen gas, difficult to maintain 1 atm pressure

2 platinum used is expensive.

2) Calomel electrode: 2Hg(l) + 2Cl^-(aq) → Hg2Cl2(s)+ 2e^{- ( oxidation half?)}

Advantages: it is, easy to set up, no salt bridge required, potential does not change with one.

disadvantages: mercury used is poisonous.

They cannot be used in measuring potentials where K+ and Cl- interfere in the reaction.

3) silver silver chloride electrode: AgCl + e Ag + Cl- ( reduction half reaction) E° 0.230V wet SHE.

Advantages: simple construction, inexpensive, stable pH, non toxic components.

Disadvantages: AgCl reacts with base and light that interfere in the potential.

4) copper copper sulfate electrode: E° 0.314V. Used in Catholic protection corrosion controlled system.

Cu²⁺ + 2e Cu ( reduction reaction) ( when used as cathode)

Advantages: does not depend on pH and is stable. Not influenced by temperature.

Disadvantages: cannot be used in basic conditions as copper hydroxide is formed