Long Answer Type(a) Account for the following:
(i) Zr and Hf have almost similar atomic radii.
(ii) Transition metals show variable oxidation states.
(iii) Cu+ ion is unstable in aqueous solution.
(b) Complete the following equations:
(i) 2 MnO2 + 4 KOH + O2--->
(ii) 2 Na2CrO4 + 2 H + -->
|
|
Cr |
Mn |
Fe |
Co |
Ni |
Cu |
|
-0.91 |
-1.18 |
-0.44 |
-0.28 |
-0.25 |
-0.34 |
From the given data of E0 values answer the following Question:
(i) Which is strongest why is value exceptionally positive?
(ii) Why is value highly negative as compared to other elements?
(iii) Reducing agent Cr2+ or Fe2+? Give reason
(b) Why do actinoids show wide range f oxidation states? Write on the similarity between the chemistry of lanthanoids and actinoids.
The E0 (M2+/M) value of a metal depends on the energy changes involved in the formation of the M2+ ion:
1. Sublimation: The energy required for converting one mole of an atom from the solid state to the gaseous state
M(s) ---> M (g) sH (Sublimation energy)
2. Ionisation: The energy required to take out electrons from one mole of atoms in the gaseous state to form the corresponding cation in the gaseous state
M (g) --->M2+ (g) iH (Ionization energy)
3. Hydration: The energy released when one mole of ions are hydrated
M (g)---> M2+ (aq) hydH (Hydration energy)
Now, copper has high energy of atomization and low hydration energy. Hence, theE0(Cu2+/Cu) is exceptionally positive.
(ii) The 
value is highly negative as compared to other elements because of the extra stability of Mn2+ due half -filled d orbitals.
(iii) The following reactions are involved when Cr2+ and Fe+ act as reducing agent:
Cr2+ ---> Cr3+ + e-
Fe2+ ----> Fe3+ + e-
The 
value is -0.41 V and 
is + 0.77V. This means that Cr2+ can be easily oxidised to Cr3+ but Fe2+ does not get oxidised to Fe3+ easily, therefore, Cr2+ is a stronger reducing agent than Fe3+.
(b) In actinoids, the 5f, 6d, 7s shells are present. These three shells are of comparable energies; therefore electrons can remove from these shells. This gives rise f variable oxidation states in actinoids.
Following are the similarities between actinoids and lanthanoids:
(i) The size of atom: It decreases across the series in both actinoids (due to actinoid contraction) and lanthanoids(due to lanthanoids contraction).
(ii) Oxidation states: Lanthanoids and actinoids generally show +3 oxidation states. However, some element in the actinoids series is capable of exhibiting oxidation states higher than +3.
Short Answer TypeHow are interhalogen compounds formed? What general compositions can be assigned to them?
Long Answer Type(a) Give reasons for the following:
(i) Mn3+ is a good oxidising agent.
(ii) 
Values are not regular for first row transition metals (3d series).
(iii) Although ‘F’ is more electronegative than ‘O’, the highest Mn fluoride is MnF4, whereas the highest oxide is Mn2O7.
(b) Complete the following equations:
(a) Why do transition elements show variable oxidation states?
(i) Name the element showing the maximum number of oxidation states among the first series of transition metals from Sc (Z = 21) to Zn (Z = 30).
(ii) Name the element which shows only +3 oxidation state.
(b) What is lanthanoid contraction? Name an important alloy which contains some of the lanthanoid metals.
Short Answer TypeExplain each of the following observations:
(i) With the same d-orbital configuration (d4), Cr2+ is a reducing agent while Mn3+ is an oxidising agent.
(ii) Actinoids exhibit a much larger number of oxidation states than the lanthanoids.
(iii) There is hardly any increase in atomic size with increasing atomic number in a series of transition metals.
When chromite ore FeCr2O4 is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).
(i)Write the formulae of the compounds (A), (B) and C.
(ii)Write one use of compound (C).
OR
Give reasons:
(i)Mn shows the highest oxidation state of +7 with oxygen but with fluorine, it shows the highest oxidation state of +4.
(ii)Transition metals show variable oxidation states.
(iii)Actinoids show irregularities in their electronic configurations.
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