why the acidic medium is used for determination of the amount if iorn in a sample of soil using standard KMnO4
MnO4^- is reduced to Mn^+2(aq) in acid medium.
MnO4^- is reduced to MnO42(s) in basic medium.
We want the first, not the second reduction.
The acidic medium is used for the determination of iron (Fe) in a sample of soil using standard KMnO4 because it facilitates the reaction between Fe(II) and KMnO4, allowing for accurate quantification.
The reaction between Fe(II) and KMnO4 is an oxidation-reduction reaction in which Fe(II) is oxidized to Fe(III), while KMnO4 is reduced to Mn(II). This reaction occurs rapidly in an acidic medium due to the following reasons:
1. Stability of KMnO4: KMnO4 is highly unstable under alkaline conditions and can decompose before it can react with Fe(II). However, in an acidic medium, KMnO4 remains stable and can react effectively.
2. Favorable redox potentials: The redox potentials of Fe(II) and KMnO4 are conducive for a reaction to occur in an acidic medium. Fe(II) is more easily oxidized to Fe(III) in an acidic environment, and KMnO4 is readily reduced to Mn(II) under similar conditions.
To carry out the determination of iron in a sample of soil using standard KMnO4 in an acidic medium, the following steps are typically followed:
1. Prepare the sample: The soil sample needs to be properly collected, dried, and ground into a homogenous powder.
2. Acidify the sample: Add a measured amount of acid, usually hydrochloric acid (HCl), to the soil sample. This acidifies the sample, providing the required acidic conditions for the subsequent reaction.
3. Extraction of iron: Extract the iron from the soil sample using a suitable extracting solution, such as ammonium oxalate or diethylene triamine pentaacetic acid (DTPA). This step helps to ensure the iron is in a soluble form and available for reaction with KMnO4.
4. Titration: Add the standardized KMnO4 solution to the acidic extract containing the iron. The pink color of the MnO4- ion in KMnO4 acts as an indicator, and it turns colorless when all the iron has reacted. By noting the volume of KMnO4 solution required to reach the endpoint, the amount of iron present in the soil sample can be calculated.
It is important to note that the acidic medium and other reagents, as well as the procedure, may vary based on the specific analytical method being used.