Acidic solutions half-reaction method

The Sample Problem on the next page illustrates the use of these steps for an acidic solution. To balance a net ionic equation for basic conditions by the half-reaction method, balance each half-reaction for acidic conditions, adjust for basic conditions, and then combine the half-reactions to obtain the balanced net ionic equation. The following Concept Organizer summarizes how to use the half-reaction method in both acidic and basic conditions. 

The following redox reactions occur in acidic solution. Balance the equations using the half-reaction method. 

Show the reaction of iron with a hydrochloric acid solution to produce H2 gas by using the oxidation-reduction half-reaction method. 

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... 

To summarize, balancing a redox reaction in acidic solution by the half-reaction method is a six-step process, followed by a check of the answer (Figure 4.4.)... 

PROBLEM 4.19 Balance the following net ionic equation by the half-reaction method. The reaction takes place in acidic solution. 

Using the half-reaction method, we separate the oxidation and reduction half-reactions and then balance. We use H2O (reaction in solution) and H+ (acid medium due to the presence of HC1). 

The half-reaction method can be applied to more complex redox reactions, such as the reaction of permanganate ion, Mn04, with Fe2+ in acidic solution. 

To balance a redox reaction which occurs in a basic solution is a very similar to balancing a redox reaction which occurs in acidic conditions. First, balance the reaction as you would for an acidic solution and then adjust for the basic solution. Here is an example using the half-reaction method ... 

The general procedure is to balance the equations for the half-reactions separately and then to add them to obtain the overall balanced equation. The half-reaction method for balancing oxidation-reduction equations differs slightly depending on whether the reaction takes place in acidic or basic solution. 

Balancing Oxidation-Reduction Equations Occurring in Acidic Solution by the Half-Reaction Method... 

Oxidation-reduction reactions can occur in basic as well as in acidic solutions. The half-reaction method for balancing equations is slightly different in such cases. 

Use the half-reaction method as specified for acidic solutions to obtain the final balanced equation as if H+ ions were present. 

Use the half-reaction method to write a balanced equation for each of the following reactions in acidic, aqueous solution. ... 

Use the half-reaction method to balance these equations. Add water molecules and hydrogen ions (in acid solutions) or hydroxide ions (in basic solutions) as needed. Keep balanced equations in net ionic form. 

For each of the following unbalanced equations, (i) write the half-reactions for oxidation and for reduction, and (ii) balance the overall equation in acidic solution using the half-reaction method. 

The Half-Reaction Method for Balancing Equations for Oxidation-Reduction Reactions Occurring in Acidic Solution... 

Iodide ion, I , is one of fhe mosf easily oxidized species. Balance each of fhe following oxidation-reduction reactions, which take place in acidic solution, by using the half-reaction method. 

The redox reaction between dichromate ion and iodide ion in acid solution is shown in Figure 19.15. Use the half-reaction method to balance the equation for this redox reaction. 

In using the half-reaction method, we usually begin with a skeleton ionic equation showing only the substances undergoing oxidation and reduction. In such cases, we usually do not need to assign oxidation numbers unless we are unsure whether the reaction involves oxidation-reduction. We will find that H (for acidic solutions), OH (for basic solutions), and H2O are often involved as reaaants or products in redox reactions. Unless, ... 

Complete and balance the following equation in acidic solution using the method of half-reactions. 

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