Reduction and Oxidation Help

By — McGraw-Hill Professional
Updated on Aug 28, 2011


Reduction is the chemical name for a decrease in oxidation number. When hydrogen is heated in combination with metal oxides like copper and zinc, the metal element is separated out and water is formed.


The example below demonstrates the reduction reaction.

CuO + H 2 ⇒ Cu + H 2 O

ZnO + H 2 ⇒ Zn + H 2 O

The metal oxide is reduced to release the uncombined metal. This is called a reduction reaction.

Reduction is what happens when a sample gains one or more electrons provided by the reducing agent. As you might guess, hydrogen can be used as a reducing agent.

Reduction also happens when a compound picks up hydrogen atoms. Methyl alcohol, CH 3 OH, is formed in the reaction of carbon monoxide (CO), hydrogen gas, and a catalyst.


CO + 2 H 2 ⇒ CH 3 OH

An atom is also reduced if it gains electrons directly. This can be seen when Cu 2+ - or Ni 2+ -containing solutions are plated onto an electrode. When electrons are removed from the electrode, the metal ions are reduced.


While studying reduction, it is a good time to look at the opposite reaction, oxidation . Oxidation is the process of a substance combining with oxygen. It is the reverse of reduction.

When silicon (Si) is combined with oxygen and other minerals in the Earth’s crust, sand is formed. In fact, most of the compounds in living organisms on this planet contain oxygen. Nearly 60% of the weight of a human body is oxygen.

Oxidationtakes place when an element gains oxygen, loses hydrogen, or loses electrons.


N 2 + O 2 + (high temperature) ⇒ 2 NO (nitric oxide)


2 H 2 S + 3O 2 ⇒ 2 H 2 O + 2SO 2

Hydrogen sulfide (H 2 S) burns in oxygen to make water and sulfur dioxide. When this is oxidized, O 2 combines with each atom of the products. Oxidation and reduction can be thought of as an “opposite theory.”

Reduction is (+) gain.

Oxidation is (–) loss.

The key to oxidation is to remember that oxidation is not just for oxygen, but it also defines a lot of different reactions with metals.

Figure 8.1 shows oxidation and reduction changes.

Basically, it is a cause and effect system. When an element causes the oxidation of another substance, it is itself reduced in the process.

The Hydrogen Atom Oxidation

Fig. 8.1. Oxidation and reduction are opposite reactions.

Redox chemistry is when one sample is reduced and another sample is oxidized at the same time during the same reaction.

Picture the “you scratch my back, I’ll scratch yours,” type of interaction. When all the atoms in a reaction shift around to find balance in filled orbitals, the compound is stable.

Oxidation and reduction are opposite reactions. An oxidizing agent is the element in the reaction that oxidizes another element, while at the same time being reduced itself. A reducing agent is the element in the reaction that reduces another element while at the same time being oxidized itself. In redox reactions, the total charge of the elements’ oxidation numbers will be equal on both sides of the equation.

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