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प्रश्न
Compare the stability of +2 oxidation state for the elements of the first transition series.
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उत्तर १
| Sc | +3 | ||||||
| Ti | +1 | +2 | +3 | +4 | |||
| V | +1 | +2 | +3 | +4 | +5 | ||
| Cr | +1 | +2 | +3 | +4 | +5 | +6 | |
| Mn | +1 | +2 | +3 | +4 | +5 | +6 | +7 |
| Fe | +1 | +2 | +3 | +4 | +5 | +6 | |
| Co | +1 | +2 | +3 | +4 | +5 | ||
| Ni | +1 | +2 | +3 | +4 | |||
| Cu | +1 | +2 | +3 | ||||
| Zn | +2 |
From the above table, it is evident that Mn exhibits the most oxidation states, ranging from +2 to +7. The number of oxidation states increases as one moves from Sc to Mn. On moving from Mn to Zn, the number of oxidation states decreases due to a decrease in the number of available unpaired electrons. The relative stability of the +2 oxidation state increases on moving from top to bottom. This is because, on moving from top to bottom, it becomes more and more difficult to remove the third electron from the d-orbital.
उत्तर २
Firstly, in the first half of the transition series, the sum of the first- and second-ionisation enthalpies increases with atomic number. Hence, the standard reducing potential (E°) is low and negative. Hence, the tendency to form M2+ ions decreases. Hence, the +2 oxidation state is more stable in the first half. The greater stability of the +2 oxidation state is due to half-filled d-subshells (d5) in Mn2+, fully filled d-subshells (d10) in Zn2+, and high negative hydration enthalpy in nickel.
संबंधित प्रश्न
Out of Mn3+ and Cr3+, which is more paramagnetic and why ?
(Atomic nos. : Mn = 25, Cr = 24)
To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.
Which of the d-block elements may not be regarded as the transition elements?
Use Hund’s rule to derive the electronic configuration of Ce3+ ion and calculate its magnetic moment on the basis of ‘spin-only’ formula.
Following are the transition metal ions of 3d series:
Ti4+, V2+, Mn3+, Cr3+
(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)
Answer the following:
1) Which ion is most stable in an aqueous solution and why?
2) Which ion is a strong oxidising agent and why?
3) Which ion is colourless and why?
Give reasons:
E° value for the Mn3+/Mn2+ couple is much more positive than that for Fe3+/Fe2+.
Why do transition metals exhibit higher enthalpy of atomization?
Two metallic elements A and B have the following standard oxidation potentials: A = 0·40v B = - 0·80v. What would you expect if element A was added to an aqueous salt solution of element B? Give a reason for your answer.
Explain why transition metals and their compounds act as a catalyst.
Explain why does colour of \[\ce{KMNO4}\] disappear when oxalic acid is added to its solution in acidic medium.
Match the solutions given in Column I and the colours given in Column II.
| Column I (Aqueous solution of salt) |
Column II (Colour) |
| (i) \[\ce{FeSO2.7H2O}\] | (a) Green |
| (ii) \[\ce{NiCl2.4H2O}\] | (b) Light pink |
| (iii) \[\ce{MnCl2.4H2O}\] | (c) Blue |
| (iv) \[\ce{CoC12,6H2O}\] | (d) Pale green |
| (v) \[\ce{Cu2 Cl2}\] | (e) Pink |
| (f) Colourless |
If enthalpies of formation of C2H4(g), CO2(g) and H2O(l) at 25°C and 1 atm pressure are 52, – 394 and – 286 kJ/mol respectively, the change in ethalpy for combustion of C2H4 is equal to
Which of the following maxm magnetic moment?
The complex showing a spin-span magnetic moment of 2.82 B.M. is :-
Which of the following species has maximum magnetic momentum?
Give a reason for the following:
Zinc, cadmium and mercury are considered as d-block elements but not regarded as transition elements.
A coordination compound has the formula \[\ce{CoCl3.4NH3}\]. It precipitates silver ions as AgCl and its molar conductance corresponds to a total of two ions.
Based on this information, answer the following question:
- Deduce the structural formula of the complex compound.
- Write the IUPAC name of the complex compound.
- Draw the geometrical isomers of the complex compound.
Give a reason for the following.
Some transition metals and their compounds get attracted towards the magnetic field.
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with iron (II) solution.
For M2+/M and M3+/M2+systems, the EΘ 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 ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
