1a) why is it advisable to prepare a slightly more conc. soln. of kMnO4 when preparing its standard solution? b) what else do u have to do? (2). what will happen if NH4Cl is used to standardized the KMnO4. (3a). A student noticed traces of brown deposit during the KMnO4 to (NH4)2Fe(SO4)2 titration and quickly add more H2SO4 and continued his titration. What will happen and why? (b) if the student added HCl instead of H2SO4 What will happen and why?
1a. Actually, I don't think it advisable to prepare a slightly more concd solution of KMnO4. I know why this as been broached and that's probably because KMnO4 is not pure straight out of the bottle and because it is reduced to MnO2 when prepared; however, my experience is that also decomposition has taken place it isn't enough to warrant trying to adjust for it.
1b. You prepare the solution and let it stand before trying to use it. You want the MnO2 to ppt.
2. You can standardize KMnO4 with NH4Cl????? Really?????
3a. The brown ppt signals that the KMnO4 is being reduced to MnO2 and not Mn^2+ so H2SO4 is added to make sure that the solution is acid enough.
3b. One doesn't use HCl with KMnO4 (although some well known procedures use it along with Zimmerman-Reinhardt solution) because KMnO4 will oxidize Cl^- and that causes too much KMnO4 to be used in the titration.
1a) It is advisable to prepare a slightly more concentrated solution of KMnO4 when preparing its standard solution because KMnO4 solutions are not stable and tend to decompose over time. By preparing a more concentrated solution, it ensures that there is still enough available MnO4- ion for the standardization process even after some decomposition has occurred.
b) To prepare the standard solution of KMnO4, you would typically need to follow these steps:
1. Weigh a known mass of KMnO4 and dissolve it in distilled water to make a solution.
2. Dilute the solution to a known volume using a volumetric flask.
3. Standardize the solution by titrating it against a known concentration of a reducing agent.
2) If NH4Cl is used to standardize the KMnO4 solution, it will react with KMnO4 and reduce it to Mn2+ ions. This reaction will interfere with the accurate determination of the KMnO4 concentration and can lead to incorrect results.
3a) If the student noticed traces of brown deposit during the KMnO4 to (NH4)2Fe(SO4)2 titration and quickly added more H2SO4 and continued the titration, it suggests the formation of the brown precipitate is likely due to the incomplete oxidation of Fe2+ to Fe3+ ions. By adding more H2SO4, the student is trying to provide more acidic conditions to facilitate the oxidation process and complete the titration accurately.
3b) If the student added HCl instead of H2SO4, it would not provide the required conditions for the oxidation reaction to occur. HCl is not a suitable oxidizing agent in this scenario, and it would not assist in completing the titration accurately.
1a) It is advisable to prepare a slightly more concentrated solution of KMnO4 when preparing its standard solution because KMnO4 is unstable in solution and can decompose over time. By preparing a more concentrated solution, you ensure that the standard solution has a higher initial concentration of KMnO4, which can compensate for any decomposition that may occur during storage.
To prepare a standard solution of KMnO4, follow these steps:
1. Weigh out a known mass of KMnO4 using a balance.
2. Dissolve the weighed KMnO4 in a small volume of distilled water in a beaker.
3. Transfer the dissolved KMnO4 solution to a volumetric flask.
4. Rinse the beaker with distilled water to transfer any remaining KMnO4 into the flask.
5. Add distilled water to the volumetric flask up to the graduation mark and mix well to obtain a homogeneous solution.
b) In addition to preparing a concentrated solution, you will also need to determine the exact concentration of the KMnO4 solution. This can be done by titrating it against a solution of a known concentration of a reducing agent, such as oxalic acid (H2C2O4). The titration allows you to calculate the concentration of the KMnO4 solution based on the stoichiometry of the reaction between KMnO4 and the reducing agent.
2. If NH4Cl is used to standardize KMnO4, it will react with KMnO4 to form ammonium manganate (NH4MnO4). This reaction is not suitable for standardizing KMnO4 because ammonium manganate is not a stable compound and can decompose further, leading to inaccuracies in the determination of KMnO4 concentration.
3a. If the student noticed traces of brown deposit during the KMnO4 to (NH4)2Fe(SO4)2 titration and quickly added more H2SO4 and continued the titration, the additional H2SO4 would help dissolve the brown deposit. The brown deposit suggests the presence of manganese dioxide (MnO2), which is formed when KMnO4 disproportionates in an acidic medium. By adding more H2SO4, the student creates a more acidic environment, which aids in the dissolution of MnO2 and allows the titration to continue.
3b. If the student added HCl instead of H2SO4, the titration would not proceed properly. HCl is not suitable for dissolving MnO2, and therefore, the brown deposit would not dissolve. This would hinder the accuracy of the titration as the presence of undissolved MnO2 would interfere with the endpoint determination. Additionally, HCl may react with KMnO4 to form chlorine gas, further affecting the titration process.