Oxidation-number method

Of course, the oxidation number method gives the same balanced equation as the half-reaction method. 

The other procedure which is of value in the calculation of the equivalents of substances is the oxidation number method. This is a development of the view that oxidation and reduction are attended by changes in electronic charge and was originally developed from an examination of the formulae of the initial and final compounds in a reaction. The oxidation number (this will be abbreviated to O.N.) of an element is a number which, applied to that element in a particular compound, indicates the amount of oxidation or reduction which is required to convert one atom of the element from the free state to that in the compound. If oxidation is necessary to effect the change, the oxidation number is positive, and if reduction is necessary, the oxidation number is negative. 

Oxidation number 851, (T) 853 rules for determining. 851 Oxidation number method 851 Oxidation-reduction cells 64 Oxidation-reduction curve 361 Oxidation-reduction indicators (T) 367 Oxidation-reduction reactions 67, 258, 360,... 

Some redox reactions may be simply balanced by inspection. However, many are complex and require the use of a systematic method. There are two methods commonly used to balance redox reactions the oxidation number method and the ion-electron method. 

To balance a redox reaction using the oxidation number method, follow the following rules ... 

In Section 20.2, a redox reaction involving copper and nitric acid is discussed. This reaction is balanced by a method called the oxidation-number method. In this lab, you will carry out this reaction, along with another redox reaction that involves a common household substance. You will practice balancing various redox reactions using both the oxidation-number method (from Section 20.2) and the half-reaction method (from Section 20.3). 

Balance redox reactions using the oxidation-number method. 

In fact, you can use oxidation numbers to balance a chemical equation by a new method. The oxidation number method is a method of balancing redox equations by ensuring that the total increase in the oxidation numbers of the oxidized element(s) equals the total decrease in the oxidation numbers of the reduced element(s). 

A summary of the steps of the oxidation number method is given below. 

In this section, you will write balanced equations for redox reactions using the oxidation number method... 

Explain why none of the steps in the oxidation number method result in equations that include electrons, e . 

Use the oxidation number method to balance the following equation for the combustion of carbon disulfide. 

In this section, you iearned how to use the oxidation number method to haiance redox equations. You now know various techniques for recognizing and representing redox reactions. In Chapter 11, you will use these techniques to examine specific appiications of redox reactions in the business worid and in your daiiy iife. 

Q O The combustion of ammonia in oxygen to form nitrogen dioxide and water vapour involves covalent molecules in the gas phase. The oxidation number method for balancing the equation was shown in an example in this section. Devise a half-reaction method for balancing the equation. Describe the assumptions you made in order to balance the equation. Also, describe why these assumptions did not affect the final result. 

Gompare the half-reaction and oxidation number methods of balancing equations. 

The following redox reactions occur in basic solution. Balance the equations using the oxidation number method. 

Consider the following reaction, balanced using the "oxidation numbers" method... 

Aqueous Reactions and Net Ionic The Oxidation-Number Method... 

Simple redox reactions can be balanced by the trial-and-error method described in Section 3.1, but other reactions are so complex that a more systematic approach is needed. There are two such systematic approaches often used for balancing redox reactions the oxidation-number method and the half-reaction method. Different people prefer different methods, so we ll discuss both. The oxidation-number method is useful because it makes you focus on the chemical changes involved the halfreaction method (discussed in the next section) is useful because it makes you focus on the transfer of electrons, a subject of particular interest when discussing batteries and other aspects of electrochemistry (Chapter 18). 

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... 

To summarize, balancing a redox reaction in acidic solution by the oxidation-number method is a six-step process, followed by a check of the answer (Figure 4.3.)... 

FIGURE 4.3 The proce- dure for balancing redox equations by the oxidation-number method. 

Worked Example 4.10 shows how the oxidation-number method is used to balance a reaction carried out in basic solution. The procedure is exactly the same as that used for balancing a reaction in acidic solution, but OH- ions are added as the final step to neutralize any H+ ions that appear in the equation. This simply reflects the fact that basic solutions contain negligibly small amounts of H+ but large amounts of OH-. 

An alternative to the oxidation-number method for balancing redox reactions is the half-reaction method. The key to this method is to realize that the overall reaction can be broken into two parts, or half-reactions. One half-reaction describes the oxidation part of the process, and the other half-reaction describes the reduction part. Each half is balanced separately, and the two halves are then added to obtain the final equation. Let s look at the reaction of aqueous potassium dichromate (K2Cr2C>7) with aqueous NaCl to see how the method works. The reaction occurs in acidic solution according to the unbalanced net ionic equation... 

Worked Example 4.12 shows how to use the method for balancing a reaction that takes place in basic solution. As in the oxidation-number method, we first balance the reaction for an acidic solution and then add OH- ions in a final step to neutralize H+. 

Redox reactions can be balanced using either the oxidation-number method or the half-reaction method. The concentration of an oxidizing agent or a reducing agent in solution can be determined by a redox titration. 

Oxidation-reduction reactions, even complex ones, can be balanced using either the half-reaction method or the oxidation number method. The half-reaction method will be discussed first, using the reaction of iron with chlorine to produce iron chloride. 

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