Reduction potential

The redox potential describes a measure of the redox chemistry. Is the Reduktions-/Oxidationspotential a material as measured under standard conditions to a standard reference half cell. In biological systems, the standard oxidation at pH 7.0 is defined against a standard hydrogen electrode, and at a hydrogen partial pressure of 1 bar.

Basics

As the name suggests, the reaction between two reactants takes place: one is reduced, the other is oxidized. In contrast to acid -base reactions where H ions ( protons) move from one partner to another, change the redox reactions electrons. That partner which receives electrons is reduced. The other partner is oxidized. Thus, the redox reaction can be divided into two half- reactions. In one is oxidized with the oxidation potential as the driving force, the other is reduced with the reduction potential as the driving force. The redox potential between two partners is the sum of the oxidation potential and reduction potential. The " prefer " one partner is oxidized and the " prefer " the other is reduced, the greater is their common redox potential in the reaction. Applies one speaks of a " redox couple ". The extent of the reducing power of a substance is described by its redox potential; This is to give the electrons and thus ready to go into the oxidized form.

• The more negative redox potential the stronger the reducing power
• Electrons flow from the redox couple to more negative potential more positive (or less negative) redox couple

Establishing a standard condition: standard potentials

Since redox potentials of external conditions such as pressure, temperature or pH are more or less strongly dependent, a condition was defined to improve the comparability, in which there are those at the electrochemical potential series half-elements. In this state, the standard conditions prevail: the pressure is 1 atm, the temperature of 298.15 K, the activity is one.

For example, potassium permanganate is a strong oxidizing agent, the oxidizing power, and thus, the redox potential but significantly depend on the pH. Potassium permanganate is mixed with a reducing agent to result in a pH of 1 manganese (II ) cations, at pH = 7, manganese (IV ) oxide ( manganese dioxide ) and pH = 14 manganate (VI) ions.

The conversion from the standard state to another state is possible at any of the Nernst equation.

Measuring and quantifying

Besides the above- mentioned calculation of the Nernst equation even, different measurement methods for the determination of redox potentials available:

The standard redox potential of the system can be determined by establishing a galvanic element with the hydrogen electrode and measuring the electrical voltage. For this, however, both systems must be in the default state.

Redox potentials are also by determining the voltage at the interconnection with the other half- element, whose redox potential is known, access. For this reason is often used as the reference element back into practice in other half members. Accessible, for example, the calomel electrode as lead with their potential fluctuations caused by temperature fluctuations at lower measurement errors than the hydrogen electrode.

As can be seen from the table that the redox potentials vary with increase or decrease of two degrees Celsius, only around 0.6 %.

Redox potentials in biochemistry

For biochemical processes are expected with the related potentials to pH 7 component? Eo '. For reactions in which protons are involved, this results in a potential difference of 0,413 V as specified in the table below.