Question

(a) a blackish brown coloured solid ‘a' when fused with alkali metal hydroxides in presence of air, produces a dark green coloured compound ‘b', which on electrolytic oxidation in alkaline medium gives a dark purple coloured compound

c. identify a, b and c and write the reactions involved. (b) what happens when an acidic solution of the green compound (b) is allowed to stand for some time? give the equation involved. what is this type of reaction called?

Answer 1

a) 
A= MnO₂ 

B= K₂MnO₄ 

C= KMnO₄

MnO₂ + 4KOH + O₂ → K₂MnO₄ + 2H₂O

MnO₄ ²⁻ →(electrolytic oxidation in alkaline solution) MnO4 ¹⁻
(green)                                                                        (purple)

b)
3MnO₄ ²⁻ + H ¹⁺ → 2MnO₄¹⁻ +MnO₂ + H₂O
                              (purple)     (black)
                               

:) Hope this helps!!!

Answer 2

Hey !!

(i) A = MnO₂ (Pyrolusite ore)  , B = K₂MnO₄ (Potassium manganate) , C = KMnO₄ (Potassium Permanganate)

REACTION INVOLVED

2MnO₂ + 4KOH + O₂ -------> 2K₂MnO₄ + 2H₂O

MnO₄²⁻ (Manganate ion )(Green) --(Electrolytic oxidation) in alkaline solution--> 2MnO₄⁻ + e⁻

(ii) In acidic medium, K₂MnO₄ changes to give purple coloured compound along with back precipitate.

 3MnO₄²⁻(Green compound) + 4H⁺ ------> 2MnO⁻₄(Purple compound) + MnO₂(Black) + H₂O

This type of reaction is called ''Disproportionation reaction''.

Good luck !!