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The D-And-f-Block Elements

Question

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i)Describe how potassium permanganate is made from pyrolusite. Write the chemical equations for the involved reactions.
ii) Describe with an example each of the oxidising actions of permanganate ion in alkaline and acidic media. What acid and alkali are usually used?

Solution

Pottassium Permanganate (KMnO₄) is prepared from Pyrolusite ore (MnO₂). The finely powdered Pyrolusite ore (MnO₂) is fused with an alkali metal hydroxide like KOH in the presensce of air or an oxidizing agent like KNO₃ to give the dark green potassium Manganate (K₂MnO₄). Potassium manganate disproportionate in a neutral or acidic solution to give potassium permanganate.

2 MnO₂ + 4 KOH + O₂ ----> 2K₂MnO₄ + 2H₂O
3 MnO₄^2- + 4H⁺ -----> 2MnO₄^- + MnO₂ + 2H₂O

Commercially potassium permanganate is prepared by the alkaline oxidative fusion ofPyrolusite ore (MnO₂) followed by the electrolytic oxidation of manganate (4) ion.

2MnO₂+ 4KOH + O₂ ---> 2K₂MnO₄ + 2H₂O
MnO₄^2- ------(electrolytic oxidation)----> MnO₄^- + e^-

ii) Equation Reduction of KMnO4 in acidic medium:
8H⁽⁺⁾ + MnO₄^(2-) + 5e^(-) ----------> Mn⁽²⁺⁾ + 4H₂O

In basic medium:
MnO₄^(-) + e^(-) ------------> MnO₄^(2-)

Thus, you can see that oxidizing effect of KMnO₄ is maximum in acidic medium and least in basic medium as in acidic medium the reduction in oxidation state of Mn is max while it is the least in basic medium.
H₂SO₄ and NaOH is used as acid and alkali.

Some More Questions From The d-And-f-Block Elements Chapter

In the series Sc (Z = 21) to Zn(Z = 30), the enthalpy of atomisation of zinc is the lowest i.e., 26, kJ mol. Why?

The E° (M²⁺/M) value for copper is positive (+ 0.34 V). What is possibility the reason for this?

How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which is a stronger reducing agent Cr²⁺ or Fe²⁺ and why?

Explain why Cu⁺ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d¹⁰ 4s¹, yet it is considered transition element. Why?

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