Oxidation-reduction balancing ionic redox equations

Use the half-reaction method to balance the redox equations. Begin by writing the oxidation and reduction half-reactions. Leave the balanced equation in ionic form. 

Balancing net ionic redox equations The simplest way to express a redox reaction is an equation that shows only the oxidation and reduction processes. In order to understand how this is done, consider the balanced equation for the reaction of iron(II) nitrate and... 

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. 

When balancing redox equations, we often find it convenient to omit the spectator ions (Section 4-3) so that we can focus on the oxidation and reduction processes. We use the methods presented in this chapter to balance the net ionic equation. If necessary we add the spectator ions and combine species to write the balanced formula unit equation. Examples 11-15 and 11-16 illustrate this approach. 

In the half-reaction method, we usually begin with a skeleton ionic equation showing only the substances undergoing oxidation and reduction. In such cases, we assign oxidation numbers only when we are unsure whether the reaction involves oxidation-reduction. We will find that (for acidic solutions), OH (for basic solutions), and H2O are often involved as reactants or products in redox reactions. Unless H, OH , or H2O is being oxidized or reduced, these species do not appear in the skeleton equation. Their presence, however, can be deduced as we balance the equation. 

Here s an overview of the ion-electron method The unbalanced redox equation is converted to the ionic equation and then broken down into two halfreactions — oxidation and reduction. Each of these half-reactions is balanced separately and then combined to give the balanced ionic equation. Finally, the spectator ions are put into the balanced ionic equation, converting the reaction back to the molecular form. (Buzzword-o-rama, eh For a discussion of molecular, ionic, and net-ionic equations, see Chapter 8.) It s important to follow the steps precisely and in the order listed. Otherwise, you may not be successful in balancing redox equations. 

Determine which of the following balanced net ionic equations represent redox reactions. For each redox reaction, identify the reactant that undergoes oxidation and the reactant that undergoes reduction. 

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... 

A few redox reactions have more than one oxidation half-reaction or more than one reduction half-reaction. Balancing the equations for these reactions is more complicated. However, the multiple half-reactions are often stoichiometricaUy hnked. Maintain the correct ratio of the elements and balance the electron transfer by multiplying them both by the same integer. Balance the following net ionic equation for a reaction in basic solution. OH" or HjO (but not H" ") may be added as necessary. 

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