# how can scientists measure the standard reduction potential of a half-cell?

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## How are the chemical reactions of the table of standard reduction potentials experimentally determined?

the standard reduction potential and its meaning is usually axiomatically presented early on and everything follows from there. What I would like to see in a treatment of the subject is an explanation of how the chemical equations of the reduction half reactions are actually determined. For example, let’s take the equation Cu2++2eCuCuX2++2eX−⟷Cu. How did they figure out that it is in fact two electrons reducing the Cu2+CuX2+ ion?

One could do open circuit potential measurements to determine the standard reduction potential, but it would seem to me that you would have to know the ionic state of the element a priori to use this technique. One could also apply a voltage until the reaction “turns on” then approximate that onset voltage as the standard reduction potential, but this wouldn’t be strictly true as it would be a non-equilibrium measurement and would also be subject to the kinetics of the surface.

## How can scientist measure the standard reduction potential of a half cell

It is possible to determine the standard reduction potential of half cell by using hydrogen electrode as a reference electrode.

The standard oxidation potential of hydrogen half cell, under standard conditions, is 0 v. Hence, when an unknown half cell (say X/X-) is clubbed with hydrogen half cell, it directly gives the half cell potential of electrode of interest.

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Such electrochemical cell can be represented as follows:

Pt/H2/H+//X-/X

Here, Eo cell = Eo X/X-  –   Eo H2/H+

But,  Eo H2/H+ = 0 V

∴ Eo cell = Eo X/X-

## Standard Reduction Potential

In an electrochemical cell, when two electrodes are connected, electrons will flow from the electrode with a higher negative charge density to the electrode with a lower one. A potential difference develops as a result of the electrode and the electrolyte (an aqueous solution that allows electricity to pass), which is defined as reduction potential. In other words, the reduction potential is the tendency of a chemical species to be reduced by taking an electron. It is denoted by the symbol E. how can scientists measure the standard reduction potential of a half-cell?

The basis of all electrochemical cells is the redox reactions, composed of two half-reactions. One is oxidation half-reaction at the anode (loss of electron occurs here), and the other is reduction half-reaction at the cathode (gain of electrons occurs here). In this way, electrons are moving through the electrolyte.

Standard reduction potential is required to determine the individual potential of a half-cell.

The reduction potential of a molecule under standard conditions (1 atm pressure, 1 M concentration, and 298 K temperature) is called standard reduction potential. It is denoted by the symbol Eo. It is now termed as standard potential as per the IUPAC convention.

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A reference electrode named standard hydrogen electrode (SHE) with 0.00 V potential is used for its determination. Determination of standard reduction potential can be done by connecting an electrode with SHE and measuring the cell potential of galvanic cell prepared. The oxidation potential and reduction potential of an electrode have a reverse relationship that is expressed in the form of a sign.

For example,

Mn++ne−→M

Cu2+(aq)+2e−→Cu

The standard reduction potential of the half-cell, ECu2+/Cuo = EReductiono = +0.34 V.

The standard oxidation potential of the half-cell, ECu/Cu2+o = EOxidationo = -0.34 V.

The reducing power of a chemical species is determined by standard reduction potential or a standard reduction table. It is also used for reaction direction determination.

Standard reduction potential is affected by certain factors such as the concentration of ionic species and temperature. This can be explained by the Nernst equation:

E = Eo – 2.303RT/nF log Q

Q = (Mn+) of oxidized species / (Mn+) of reduced species.