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?

Question

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?

DrBob222 · Accepted Answer

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.