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# For M2+/M and M3+/M2+ systems, the Eθ values for some metals are as follows - Chemistry

ConceptSome Important Compounds of Transition Elements - Oxides and Oxoanions of Metals

#### Question

For M2+/M and M3+/M2+ systems, the E^theta values for some metals are as follows:

Cr2+/Cr −0.9V

Cr3/Cr2+ −0.4 V

Mn2+/Mn −1.2V

Mn3+ /Mn2+ +1.5 V

Fe2+ /Fe −0.4V

Fe3+/Fe2+ +0.8 V

Use this data to comment upon:

(i) The stability of Fe3+ in acid solution as compared to that of Cr3+ or Mn3+ and

(ii) The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.

#### Solution

(1)The E^theta value for Fe3+/Fe2+ ­­ is higher than that for Cr3+/Cr2+ and lower than that for Mn3+/Mn2+. So, the reduction of Fe3+ to Fe2+ is easier than the reduction of Mn3+ to Mn2+, but not as easy as the reduction of Cr3+ to Cr2+. Hence, Fe3+ is more stable than Mn3+, but less stable than Cr3+. These metal ions can be arranged in the increasing order of their stability as: Mn3+ < Fe3+ < Cr3+

(2)The reduction potentials for the given pairs increase in the following order.

Mn2+ / Mn < Cr2+ / Cr < Fe2+ /Fe

So, the oxidation of Fe to Fe2+ is not as easy as the oxidation of Cr to Cr2+ and the oxidation of Mn to Mn2+. Thus, these metals can be arranged in the increasing order of their ability to get oxidised as: Fe < Cr < Mn

Is there an error in this question or solution?

#### APPEARS IN

NCERT Solution for Chemistry Textbook for Class 12 (2018 to Current)
Chapter 8: The d-block and f-block Elements
Q: 17 | Page no. 235

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Solution For M2+/M and M3+/M2+ systems, the Eθ values for some metals are as follows Concept: Some Important Compounds of Transition Elements - Oxides and Oxoanions of Metals.
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