Ion electron method

The complete rules for the application of the ion-electron method may be expressed as follows ... 

There are two essentially different methods to balance redox reactions—the oxidation number change method and the ion-electron method. The first of these is perhaps easier, and the second is somewhat more useful, especially for electrochemical reactions (Chap. 14). 

In the ion-electron method of balancing redox equations, an equation for the oxidation half-reaction and one for the reduction half-reaction are written and balanced separately. Only when each of these is complete and balanced are the two combined into one complete equation for the reaction as a whole. It is worthwhile to balance the half-reactions separately since the two half-reactions can be carried out in separate vessels if they are suitably connected electrically. (See Chap. 14.) In general, net ionic equations are used in this process certainly some ions are required in each half-reaction. In the equations for the two half-reactions, electrons appear explicitly in the equation for the complete reaction—the combination of the two half-reactions—no electrons are included. 

Ion-electron method a method of balancing redox equations using ions in half-reactions. 

The equation then is balanced with the ion-electron method. 

B We begin by translating names into formulas. Mn02 (s) + HCl(aq) -> Mn2+ (aq) + Cl2 (aq) Then we produce a balanced net ionic equation with the ion-electron method. 

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 ion-electron method, follow the following rules (Several variations of this method are used.)... 

We have seen how analytical calculations in titrimetric analysis involve stoichiometry (Sections 4.5 and 4.6). We know that a balanced chemical equation is needed for basic stoichiometry. With redox reactions, balancing equations by inspection can be quite challenging, if not impossible. Thus, several special schemes have been derived for balancing redox equations. The ion-electron method for balancing redox equations takes into account the electrons that are transferred, since these must also be balanced. That is, the electrons given up must be equal to the electrons taken on. A review of the ion-electron method of balancing equations will therefore present a simple means of balancing redox equations. 

Balancing the equation using the ion-electron method results in the following (check it) ... 

Balancing the equation using the ion-electron method results in the following (check it) 5 H202 + 6 H 2 Mn04 ->502 + 2 Mn2+ + 8 H20 Calculating the percent hydrogen peroxide utilizes Equation (4.37) from Chapter 4 ... 

Balancing Redox Equations Using the Ion-Electron Method... 

This reaction could be written in the ion-electron method as... 

One of the main purposes for using oxidation numbers is to follow the movement of electrons during an oxidation-reduction reaction. Doing so helps to predict the products and determine the outcomes of such reactions. There are a few different ways to analyze redox reactions, but we will focus on only one the ion-electron method (also called the half-reaction method). The procedure requires that you know the reactants and products of the reaction, but, by going through the process, you will gain a better understanding of the mechanisms by which these reactions proceed. 

Box 6.5 How to balance redox equations from partial ionic equations using the ion-electron method... 

For brevity, we will refer to this as the HR method. It is sometimes referred to as the ion-electron method. 

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. 

Solved Problem 10.5 Complete and balance the following equation in acid solution using the ion-electron method. 

The principles of oxidation-reduction provide the basis of two simple systematic methods for balancing these equations. If all the products of reaction are known, the balancing may be done either by the ion-electron method or by the oxidation-state method. (The two methods are compared following Problem 11.8.) After students have acquired more experience, they will be able to predict some or all of the principal products if they keep in mind such facts as the following ... 

Ion-Electron Method. (Steps are numbered to correspond to the rules on the preceding page.)... 

The first partly filled skeleton equation could have been written in terms of NOJ rather than H NO). For variety in the subsequent solved problems, the neutral-compound notation will be used in the oxidation-state method, and the ionic notation in the ion-electron method. 

In problems like the above, involving unusual oxidation states, the student may ask, What will happen if I choose the wrong oxidation numbers The answer is that the same result will be obtained so long as the method is followed consistently. If one chooses to assign +4 to the Fe and -2 to the S in the above example the total oxidation state increase is still 11. An advantage of the ion-electron method is that such decisions are avoided, since the oxidation state is not used to determine the electron change. 

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