kintatw asked in 科學及數學化學 · 1 decade ago

急--titration of Fe(NH4)2(SO4)2.xH2O and KMnO4

State the functions of sulphuric acid.Guess what happens if aqueous sulphuric acid is not enough in this titration.


can you give more functions of sulphuric acid?

1 Answer

  • 1 decade ago
    Favorite Answer

    Sulphuric acid is used to acidify the reaction mixture.

    In a strongly acidic medium, MnO4-(aq) is reduced to colourless Mn2+(aq), while Fe2+(aq) is oxidized to yellow Fe3+(aq).

    The end point is reached when the solution turns pale pink (or pale purple) due to a slight excess of MnO4-.

    MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) → Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)

    If the solution is not strongly acidic enough or even neutral, Fe2+(aq) is also oxidized to Fe3+(aq) by the MnO4. However, MnO4-(aq) is reduced to MnO2(s), which is a brown solid. In the presence of brown MnO2 solid, the end point colour (pale pink or pale purple) is difficult to determine.

    MnO4-(aq) + 4H+(aq) + 3Fe2+(aq) → MnO2(s) + 2H2O(l) + 3Fe3+(aq)

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