Acidic solution balancing half reactions

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. 

Each of the oxidation-reduction reactions place in acidic solution. Balance each reaction by using the half-reaction method. 

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. 

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 reduction of permanganate ions, Mn04, to manganese(II) ions in an acidic solution. 

Write a balanced half-reaction equation for the oxidation of Mo3+ t0 MoO in acid 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. 

Write the balanced half-reaction for the conversion of HOBr(a ) to Br2(a ) in acidic solution. 

You can answer these questions by writing the complete, balanced half-reactions for each case. Then, analyse each half-reaction if either H or OH" appear on any side of reaction, the potential of the half-reaction is going to depend on the pH of the solution. Once you have determined this, write down the Nemst equation and see how the potential changes with change in acidity of your solution. If you have problems writing the balanced halfreactions, consult Section 5.1 and worked Example 5.1. 

In alkaline solution it is more appropriate to use OH- rather than IT1" (see Topic E2). The other species present may also be different from those in acid, as many metal cations form insoluble hydroxides or even oxoanions (see Topic E4). As an example, consider the reaction of aluminum metal with water to form [Alm(OH)4]- and H2. The balanced half reactions are... 

The standard dichromate (Cr207 ) ion/chromium(III) ion half-cell consists of a 1 M Pt/Cr2072-(i M), Cr +(1 M) concentration of each of the two ions in contact with an inert electrode. The balanced half-reaction in acidic solution (1.0 M H ) is... 

Write balanced half reactions for the following redox couples in acidic solution C104 /C103, C103 /HC102, HCIO2/HCIO, HCIO/CI2, cycr. (The only other species required for balancing are H2O and H+.)... 

Write complete balanced half-reactions for (a) oxidation of nitrous acid to nitrate ion in acidic solution, (b) oxidation of N2 to N2O in acidic solution. 

Write the balanced half-reactions and a balanced redox equation for each of the following reactions in acidic solution (15.3)... 

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

The compound P4S, is oxidized by nitrate ions in acid solution to give phosphoric acid, sulfate ions, and nitric oxide, NO. Write the balanced equation for each half-reaction and the overall equation for the reaction. 

Step 3 If oxygen appears in any formula on either side in either equation, it is balanced by writing H20 on the opposite side. This is possible since the reaction mixture is a water solution. The hydrogen in the water is then balanced on the other side by writing H1, since we are dealing with acid solutions. Now balance both half-reactions for all elements by inspection. 

The following steps are used to balance a half-reaction for an acidic 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. 

Write balanced ionic half-reaction equations for the oxidation of each of the following reducing agents in acid solution. 

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.)... 

Balance the half-reactions in Problem 4.70, assuming that they occur 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). 

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 ... 

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