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प्रश्न
For M2+/M and M3+/M2+ systems, the E° values for some metals are as follows:
| Cr2+/Cr | −0.9 V |
| Mn2+/Mn | −1.2 V |
| Fe2+/Fe | −0.4 V |
| Cr3/Cr2+ | −0.4 V |
| Mn3+/Mn2+ | +1.5 V |
| Fe3+/Fe2+ | +0.8 V |
Use this data to comment upon:
- The stability of Fe3+ in acid solution as compared to that of Cr3+ or Mn3+ and
- the ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
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उत्तर
- The value of E° for Cr3+/Cr2+ is negative. Hence, Cr3+ is stable and cannot be reduced to Cr2+. The value of E° for Mn3+/Mn2+ is more positive; hence, Mn3+ is not very stable and can easily be reduced to Mn2+. The value of E° for Fe3+/Fe2+ is less positive but smaller. Hence, Fe3+ is more stable than Mn3+, but it is less stable than Cr3+
- The oxidation potentials for Fe, Cr, and Mn are +0.4 V, +0.9 V, and +1.2 V, respectively. Hence, the order of ease of oxidation of these is Mn > Cr > Fe.
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संबंधित प्रश्न
Give reasons:
Transition metals show variable oxidation states.
Explain why Cu+ ion is not stable in aqueous solutions?
How would you account for the following:
Cobalt (II) is stable in aqueous solutions, but in the presence of complexing reagents, it is easily oxidised.
Write down the number of 3d electrons in the following ion:
Cu2+
Indicate how would you expect the five 3d orbitals to be occupied for this hydrated ion (octahedral).
NF3 is possible, but NF5 is not. Why?
Give reasons:
E° value for the Mn3+/Mn2+ couple is much more positive than that for Fe3+/Fe2+.
Give reasons: Sc3+ is colourless in aqueous solution whereas Ti3+ is coloured.
The transition metals show _________ character because of the presence of unpaired· electrons and Cu+ is ____________ because of its electronic configuration is [Ar]3d10
Why do transition elements show variable oxidation states ? In 3d series (Sc to Zn), which elements shows the maximum number of oxidation state and why ?
Transition elements show magnetic moment due to spin and orbital motion of electrons. Which of the following metallic ions have almost same spin only magnetic moment?
(i) \[\ce{Co^{2+}}\]
(ii) \[\ce{Cr^{2+}}\]
(iii) \[\ce{Mn^{2+}}\]
(iv) \[\ce{Cr^{3+}}\]
Why EΘ values for Mn, Ni and Zn are more negative than expected?
When a brown compound of manganese (A) is treated with \[\ce{HCl}\] it gives a gas (B). The gas taken in excess, reacts with \[\ce{NH3}\] to give an explosive compound (C). Identify compounds A, B and C.
The second and third rows of transition elements resemble each other much more than they resemble the first row. Explain why?
Transition metals can act as catalysts because these can change their oxidation state. How does \[\ce{Fe(III)}\] catalyse the reaction between iodide and persulphate ions?
Which of the following is non-metallic?
Account for the following:
Sc3+ is colourless whereas Ti3+ is coloured in an aqueous solution.
Consider the following standard electrode potential values:
\[\ce{Sn^{2+}_{ (aq)} + 2e^- -> Sn_{(s)}}\]; E0 = −0.14 V
\[\ce{Fe^{3+}_{ (aq)} + e^- -> Fe^{2+}_{ (aq)}}\]; E0 = +0.77 V
What is the cell reaction and potential for the spontaneous reaction that occurs?
Write the number of unpaired electrons in Cr3+.
(Atomic number of Cr = 24)
Give a reason for the following:
Transition metals possess a great tendency to form complex compounds.
Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following point:
Ionisation enthalpies
