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.
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.
(i) Outer electronic configuration f Mn is 3d5 4s2.
Outer electronic configuration of Mn3+ is 3d4 4s0.
Now Mn3+ is a strong oxidizing agent. A good oxidizing agent reduces itself. I.e. gains electrons from other. Its tends to gain one more electron to acquire stable electronic configuration. If it gains one electron, its configuration will be 3d5, which is stable .this is the reason, it acts as a good reducing agent.
Cr2+ is strongly reducing agent in nature. It has d4 configuration. While acting as a reducing agent, it gets oxidized to Cr3+ such as d3. This d3 configuration can be written as t32g configuration, which is more stable configuration.
(ii) 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:
(a) The size of atom: It decreases across the series in both actinoids (due to actinoid contraction) and lanthanoids (due to lanthanoids contraction).
(b) 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
(iii) The atomic sizes of the elements of the first transition series are smaller than those of the heavier elements (elements of 2nd and 3rd transition series).
However, the atomic sizes of the elements in the third transition series are virtually the same as those of the corresponding members in the second transition series. This is due to lanthanoid contraction.
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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