Balancing equations oxidation number change method

Balance the following equation by the oxidation number change method ... 

Balance the equation for the reduction of HNO3 to NH4NO3 by Mn by the oxidation number change method. Add other compounds as needed. 

One important use of oxidation numbers is in balancing redox equations. There are essentially two methods to balance redox reactions the oxidation number change method and the ion-electron method. In the former method, the changes in oxidation number are used to balance the species in which the elements that are oxidized and reduced appear. The numbers of atoms of each of these elements is used to give equal numbers of electrons gained and lost. If necessary, first balance the number of atoms of the element oxidized and/or the number of atoms of the element reduced. Then, balance by inspection, as was done in Chapter 7. 

Section 16.1 introduces the concept of oxidation number and how to calculate the oxidation number of an element from the formula of the compound or ion of which it is a part. Section 16.2 describes how to use the oxidation numbers to name compounds, formalizing and extending the rules given in Chapter 6. Section 16.3 shows how to predict possible oxidation numbers from the position of the element in the periodic table and how to use these oxidation numbers to write probable formulas for covalent compounds. Section 16.4 presents a systematic method for balancing equations in which oxidation numbers change. 

In section 10.2, you learned that a redox reaction involves changes in oxidation numbers. If an element undergoes oxidation, its oxidation number increases. If an element undergoes reduction, its oxidation number decreases. When balancing equations by the half-reaction method in section 10.3, you sometimes used oxidation numbers to determine the reactant(s) and product(s) in each half-reaction. 

The key to the oxidation-number method of balancing redox equations is to realize that the net change in the total of all oxidation numbers must be zero. That is, any increase in oxidation number for the oxidized atoms must be matched by a corresponding decrease in oxidation number for the reduced atoms. Take the reaction of potassium permanganate (KMn04) with sodium bromide in aqueous acid, for example. An aqueous acidic solution of the purple permanganate anion (Mn04 ) is reduced by Br- to yield the nearly colorless Mn2+ ion, while Br- is oxidized to Br2. The unbalanced net ionic equation for the process is... 

The first step in any method of balancing oxidation-reduction equations is to identify the element that is oxidized and the one that is reduced. Because the change in oxidation number is equal to a change in the number of electrons controlled, and the electrons must be controlled by some atom, the total gain in oxidation number is equal to the total loss in oxidation number. The oxidation half of a reaction may be written in one equation, and the reduction half in another. Neither half-reaction can be carried out without the other, but they can be done in different locations if they are connected in such a way that a complete electrical circuit is made (Chapter 17). The half-reaction method is illustrated by balancing the equation for the reaction of zinc metal with dilute nitric acid to produce ammonium ion, zinc ion, and water ... 

Most redox equations can be balanced and (2) the change-in-oxidation-number method. Many redox equations can be balanced... 

In the following examples, we use the change-in-oxidation-number method, a system for balancing more complicated redox equations. 

Ionic equations can also be balanced using the change-in-oxidation-number method shown in Example 17.6. To illustrate this method, let s use the equation from Example 17.10. 

Balance each of the following equations using the change-in- oxidation number method ... 

Analyze and Plan We are told that the reaction of NH2OH and Cu produces N2 and Cu. We are asked to write a balanced equation for the reaction. Because the Cu and N change oxidation numbers during the reaction, this is a redox reaction, and it can be balanced by the method of half-reactions discuss in Section 20.2. 

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