In Fe(II) -`MnO_(4)^(-) "tirtration" HNO_(3)` is not used beacause:

Options

A. `"it oxidises" Mn^(2+)`
B. `"it reduces" MnO_(4)^(-)`
C. `"it oxidise" Fe^(2+)`
D. `"it reduces" Fe^(3+)"formed"`

Answer

To solve the question regarding why HNO3 is not used in the Fe(II) - MnO4^(-) titration, we can follow these steps:

### Step 1: Understand the Reaction
In the titration of Fe(II) with MnO4^(-), the MnO4^(-) ion acts as an oxidizing agent. It oxidizes Fe(II) ions (Fe²⁺) to Fe(III) ions (Fe³⁺) while being reduced to Mn²⁺.

**Hint:** Remember that in redox reactions, one species is oxidized and another is reduced.

### Step 2: Identify the Role of HNO3
HNO3 (Nitric acid) is also an oxidizing agent. If HNO3 is present in the solution, it can oxidize Fe(II) ions to Fe(III) ions before the titration with MnO4^(-) occurs.

**Hint:** Consider how the presence of multiple oxidizing agents can affect the outcome of a titration.

### Step 3: Consequences of Using HNO3
If HNO3 oxidizes Fe(II) to Fe(III), the amount of Fe(II) available for reaction with MnO4^(-) will decrease. This will lead to a lower titration value, meaning that the endpoint of the titration will not accurately reflect the concentration of Fe(II) present.

**Hint:** Think about how the stoichiometry of the reaction changes when the concentration of reactants is altered.

### Step 4: Conclusion on Acid Choice
Due to the oxidizing nature of HNO3, it is not suitable for this titration. Instead, H2SO4 (sulfuric acid) can be used because it does not oxidize Fe(II) to Fe(III), allowing for an accurate titration.

**Hint:** Consider the properties of different acids and how they interact with the substances in the reaction.

### Final Answer
HNO3 is not used in the Fe(II) - MnO4^(-) titration because it is an oxidizing agent that can convert Fe(II) to Fe(III), thus decreasing the titration value of Fe(II) by MnO4^(-).