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.
(a) The ability of the transition metal to exhibit variable valency is generally attributed to the availability of more electrons in the (n-1)d orbitals which are closer to the outermost ns orbital in energy levels.
Thus in the case of iron, we get the divalent Fe(II) state when only the 2 electrons in the 4s orbital are removed. And we get the trivalent Fe(III) state when one more 3d electron is removed, in addition to the two 4s electrons from the neutral Fe atom.
(i) Mn shows a maximum number of oxidation states among the first series of transition metals from Sc to Zn. Mn exhibits all the oxidation states from +2 to +7.
(ii) Scandium shows only +3 oxidation state.
(b) The regular decrease in the size of the atoms and ions with increasing atomic number is known as lanthanide contraction. It arises because as we move along the lanthanide series, the nuclear charge increases by one unit at each successive element, the new electron is added into the same subshell (viz., 4f). As a result, the attraction on the electrons by the nucleus increases and this tends to decrease the size. Further, as the new electron is added into the f-subshell, there is imperfect shielding of one electron by another in this subshell due to the shapes of these f-orbitals. This imperfect shielding is unable to counterbalance the effect of the increased nuclear charge. Hence, the net result is a contraction in the size though the decrease is very small.
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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