The Oxidation-Reduction Potential
Potential means “the inherent capacity for coming into being.” You see a child kicking legs in the air and you say, this one has a potential for becoming a champion in karate.
also means “existing in possibility.” One looks at Mount St. Helens
steaming and says, there is a potential for volcanic eruption.
electricity it means the difference in electrical charge between two
points. This difference creates a possibility of discharge from the
highly charged point to the lesser charged point.
the illustrations above, interactions between thunderclouds and air
cause electrical energy to accumulate in parts of the clouds close to
earth. As these electrical charges accumulate, they press to go and
when the cloud comes low, they discharge to the ground; like a crowd
pressing against locked gates. With enough pressure, the gates break
open and the crowd rushes in.
|This electrical pressure to discharge is a potential, and
in electricity we measure it in units called Volts, after the Italian
physicist, Conte Alessandro Volta (1745-1827), Professor of Physics at
the University of Pavia from 1779.
||The volt is the pressure that pushes the current down the line through the lamp.
Oxidation is the action of combining with oxygen. When an element joins with oxygen, it loses electrons to the oxygen. We expand the concept and say that any time a substance loses electrons; it is “oxidized,” regardless of whether it lost the electrons to oxygen or to another element or compound. Chlorine, for example is very attractive to electrons, thus a strong oxidizer.
is the reverse of oxidation. It is a reaction in which atoms or
molecules either lose oxygen or gain electrons. Oxidation and reduction
always happen together: an oxidizer (oxidant) is being reduced and a
reducer (reductant) is getting oxidized. When oxygen combines with
hydrogen to make water, the hydrogen is oxidized and the oxygen has been reduced.
oxygen is hungry for electrons and the hydrogen cannot hold strong
enough to its single electron in the presence of such a strong
affinity. They end up bonding together in the common share of electrons.
stands for Oxidation-Reduction Potential. In some parts of the world,
it is also known as Redox Potential. The two chemical reactions are
really "joined at the hip" - one cannot occur without the other also
Chemicals like pure oxygen, ozone, hydrogen peroxide, sodium persulfate and sodium permanganate crave electrons, always; they are all oxidizers.
is their ability to oxidize - to "snatch" electrons from other substances - that makes them good decontaminators of groundwater that is polluted with petroleum products; because, in altering the chemical makeup of the unwanted pollutants they "burn them up," leaving carbon dioxide and water as the by-product.
Of course, in the process of oxidizing, all of these oxidizers are reduced - so they lose their ability to further oxidize things. To make sure that the chemical process continues to the very end, you must have a high enough supply of oxidizer in the water to do the whole job.
But how much is "enough?" That's where the term Oxidation-Reduction Potential (ORP)
comes into play. In talking about ORP, we are actually talking
about electrical potential or voltage. We are reading the very tiny
voltage generated when a metal is placed in water in the presence of
oxidizing and reducing agents.
These voltages give us an indication of the ability of the oxidizers in the water to burn off the contaminants.
we had a body of water in which the total electron-attraction power of the oxidizers exactly equaled the total electron-giving “weakness” of the reducers (e.g. the polluting chemicals), then the amount of potential generated at the measuring electrode would be exactly zero. The water would be in pretty sad shape, because if any additional contaminants were introduced into the water, there would be no oxidizer left to handle it—all have been “spoken for.”
Through the measurement of Oxidation-Reduction Potential we monitor the oxidation of the pollutants to the achievement of our groundwater cleanup objectives.