Basic solutions balancing half reactions

Redox reactions do not always take place under neutral conditions. Balancing half-reactions is more complicated for reactions that take place in acidic or basic solutions. When an acid or base is present, or OH ions must also be considered. However, the overall approach is similar. This approach involves writing the correct formulas for the reactants and products, balancing the atoms, and adding the appropriate number of electrons to one side of the half-reaction to balance the charges. 

Write a balanced half-reaction that shows the oxidation of thiosulfate ions, 8203 , to sulfite ions, SOs ", in a basic solution. 

Step 4 In acidic solution, balance O by using H20, then balance H by using H+. In basic solution, balance O by using H20 then balance H by adding HzO to the side of each half-reaction that needs H and adding OH- to the other side. 

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. 

For acidic solutions, balance the hydrogen in each half-reaction by adding H3O+ and H2O to opposite sides of the reaction for basic solutions, add OH and H2O to opposite sides of the reaction. 

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution. Identify the oxidizing agent and reducing agent in each reaction. 

Iron(Il) hydrogen phosphite, FeHPO, is oxidized by hypochlorite ions in basic solution. The products are chloride ion, phosphate ion, and iron(lll) hydroxide. Write the balanced equation for each half-reaction and the overall equation for the reaction. 

C21-0070. In basic aqueous solution, A1 acts as a strong reducing agent, being oxidized to AIO2. Balance this half-reaction, and determine balanced net reactions for A1 reduction of the following (a) NO3 to NH3 (b) H2 O to H2 and (c) Sn03 to Sn. 

The following steps are used to balance a half-reaction for a basic solution. The Sample Problem that follows applies these steps. 

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 basic solution. Use the half-reaction method to balance the equations. 

PROBLEM 4.20 Balance the following equation by the half-reaction method. The reaction takes place in basic solution. 

Balance the half-reactions in Problem 4.71, assuming that they occur in basic 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 Basic Solution by the Half-Reaction Method... 

Balance the following oxidation-reduction reactions, which occur in basic solution, using the half-reaction method. 

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. 

Many redox reactions are too difficult to balance by the simple methods of logical reasoning described in Section 2.4. Here, we outline a systematic procedure based on half-reactions and apply it to reactions that occur in acidic or basic aqueous solution. In these reactions, water and (acidic solution) or OH ... 

Frequently we need more oxygen or hydrogen to complete the mass balance for a reaction or half-reaction in aqueous solution. We must be careful, however, not to introduce other changes in oxidation number or to use species that could not actually be present in the solution. We cannot add H2 or O2 to equations because these species are not present in aqueous solutions. Acidic solutions do not contain significant concentrations of OH ions. Basic solutions do not contain significant concentrations of H+ ions. 

We are given the formulas for two reactants and two products we write as much of the equations as possible. The reaction occurs in basic solution we can add OH and H2O as needed. We construct and balance the appropriate half-reactions, equahze the electron transfer, add the half-reactions, and eliminate common terms. 

Add the two half-reactions together, canceling out species that appear on both sides of the reaction. Since the reaction occurs in basic solution and there are 4 H ions on the right side, 4OH need to be added to both sides. Combine the H and OH where appropriate to make water molecules to write the final balanced equation ... 

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

A redox reaction consists of two parts or half-reactions. These are the oxidation reaction in which a substance loses or donates electrons and the reduction reaction in which a substance gains or accepts electrons. An oxidation reaction and a reduction reaction must always be coupled because "free" electrons cannot exist in solution and electrons must be conserved. The coupling between the two half-reactions is by the electrons that are either generated (by oxidation) or consumed (by reduction). We will use this fact in our technique for balancing redox reactions, which basically is a stepwise stoichiometric (mass) balancing of each constituent followed by a balancing of charge (electroneutrality). 

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