Reference Electrodes: Concept, Types, and Examples

Reference Electrodes: To make a potential measurement, you’ll need at least two electrodes. Those two electrodes are known as the indicator and reference electrodes in potentiometry. The reference electrode must be built so that its composition is fixed and its response is stable over time, with observed variations in measured potential owing only to changes in analyte concentration for the measured potential to be meaningful in this context.

In this article, we will learn about a primary reference electrode and its type, i.e., standard hydrogen electrode and calomel electrode. You will also understand the construction and working of standard hydrogen electrodes and calomel electrodes, the advantages of the reference electrode, etc.

What is Reference Electrode?

The electrode potential of any other electrode that can be measured is called a reference electrode. In other words, the electrode whose half-cell potential is known and is constant and completely insensitive to the composition of the solution is called a reference electrode. The reference electrode can act as both anode or cathode depending upon the nature of other electrodes.

Types of Reference Electrodes

The reference electrodes are classified into two types:

  1. Primary reference electrode: The standard hydrogen electrode is called a primary reference electrode.
  2. Secondary reference electrode: The electrode whose potential is determined by connecting to the standard hydrogen electrode is called a secondary reference electrode.
    Example: Calomel electrode

What is Electrode Potential?

The electrical difference (electromotive force) set up between the metal and its ion in the solution is electrode potential. The electrode potential is also defined as the tendency of an electrode to lose or gain electrons when it’s in contact with the solution of an ion. The electrode potential is termed oxidation potential. Suppose the oxidation occurs at the electrode concerning the reference electrode. In that case, it is called reduction potentials if the reduction occurs at the electrode concerning the reference electrode like a standard hydrogen electrode, calomel electrode, etc.

In the half cell, the metal electrode is suspended in a solution of one molar concentration at 

298K,

298K, and the electrode potential is called standard electrode potential. It is represented by the symbol 

E

.

E∘.

Standard Hydrogen Electrode

A standard hydrogen electrode is a primary reference electrode used to determine the electrode potential of a cell. The absolute value of the electrode potential of a single electrode cannot be determined because oxidation half-reaction or reduction half-reaction cannot take place alone. It is measured using reference electrodes like standard hydrogen electrodes, calomel electrodes, etc.

Saturated Calomel Electrode (SCE)

Generally, 

0.1M,1M

0.1M,1M, or a saturated solution of 

KCl

KCl is used in a calomel electrode. The calomel electrode in which the saturated solution of 

KCl

KCl is used is called the saturated calomel electrode. The emf of the calomel electrode depends upon the concentration of 

C

l

Cl– ions in the solution.

Measurement of Electrode Potential

To determine the electrode potential of an electrode, a cell is set up using the electrode as one of the electrodes and the second electrode as the reference electrode. The emf of the cell is measured. The emf of the cell is the sum of the oxidation potential and reduction potential of the cell.

The direction of the flow of current indicates whether the oxidation takes place or reduction takes place on the electrode under the investigation with respect to the reference electrode. According to this, the electrode potential is termed oxidation potential or reduction potential.

Reading on the voltmeter will be obtained only if the positive terminal of the voltmeter has been connected to the positive electrode, i.e., on which reduction occurs and the negative terminal to the negative electrode, i.e., on which oxidation occurs.

Reference Electrodes in Potentiometry

Potentiometry is used to find the concentration of a solute in a solution. In this method, the potential between two electrodes is measured using a high impedance voltmeter. One electrode is the reference electrode, and the other is the test electrode. The most common reference electrode used in potentiometry is the saturated calomel electrode 

Applications of Reference Electrodes

Application of standard hydrogen electrode

  1. It can be used to determine a range of 
  2. pH
  3. pH values of solutions.
  4. The electrode potential of the standard hydrogen electrode is zero. Therefore, the electrode potential of another electrode can be easily calculated.
    Application of calomel electrode
  5. It is used to measure 
  6. pH
  7. pH and electrical potential of the solution.

Silver chloride reference electrode

A recommendation electrode has a recognized electrode ability and is safe and secure. Its high stability is accomplished by using the redox system, which should consist of saturated concentrations in each of the participating solutions of the reaction. Usage reference electrodes are various, yet among one of the most crucial remains in the electrochemical cell. This is where it’s taken advantage of as a fifty per cent cell in the electrochemical cell to permit the resolution of the various partner’s cell capacity. They are used in electrochemical dimensions and devices like the DPV and electrochemical biosensors, specifically. A Silver chloride reference electrode is a sort of reference electrode typically used in electrochemical dimensions. For environmental reasons, it has frequently transformed the saturated calomel electrode.