The copper–copper(II) sulfate electrode is a

reference electrode A reference electrode is an electrode that has a stable and well-known electrode potential. The overall chemical reaction taking place in a cell is made up of two independent half-reactions, which describe chemical changes at the two electrodes. ...

of the first kind, based on the

redox Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

reaction with participation of the metal (

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

) and its salt,

copper(II) sulfate Copper(II) sulfate is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered hydrate of copper(II) sulfate, whi ...

. It is used for measuring

electrode potential An electrode is an electrical conductor used to make contact with a nonmetallic part of a Electronic circuit, circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can c ...

and is the most commonly used reference electrode for testing

cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded " sacrifi ...

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

control systems. The corresponding equation can be presented as follow: :Cu²⁺ + 2e⁻ → Cu⁰(metal) This reaction is characterized by reversible and fast electrode kinetics, meaning that a sufficiently high current can be passed through the electrode with 100% efficiency of the redox reaction ( dissolution of the metal or cathodic deposition of the copper-ions). The

Nernst equation In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction ( half-cell or full cell reaction) from the standard electrode potential, absolute tempera ...

below shows the dependence of the potential of the copper-copper(II) sulfate electrode on the activity or

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...

copper-ions: :

E=0.337 + \frac \ln a_

Protopopoff, et al, p. 15, Eq 2 The potential of a copper–copper sulfate electrode is +0.314

volt The volt (symbol: V) is the unit of electric potential, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

with respect to the

standard hydrogen electrode In electrochemistry, the standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 ° ...

Design

Commercial reference electrodes consist of a plastic tube holding the copper rod and saturated solution of copper sulfate. A porous plug on one end allows contact with the copper sulfate

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

. The copper rod protrudes out of the tube. The negative lead of a

voltmeter A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit. A ...

is connected to the copper rod.

Applications

A copper–copper(II) sulfate electrode is used as one of the

half cell In electrochemistry, a half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electri ...

s in the galvanic Daniel-Jakobi cell. Copper-copper(II) sulfate electrodes are used in the Copper coulometer. It contains two identical copper electrodes immersed in a slightly acidic pH-buffered solution of

Notes

References

* E. Protopopoff and P. Marcus, Potential Measurements with Reference Electrodes, Corrosion: Fundamentals, Testing, and Protection, Vol 13A, ASM Handbook, ASM International, 2003, pp. 13–16 * A.W. Peabody, Peabody's Control of Pipeline Corrosion, 2nd Ed., 2001, NACE International. Electrodes Corrosion prevention {{electrochem-stub