Solutions-Class-12-Chemistry-Chapter-8-Transition and Inner transition Elements-Maharashtra Board

(d) Sc³⁺

(c) +4

(c) Ni, Cr

(b) +4

(d) +3, +6

(c) 3d¹⁰, 4s¹; 3d¹⁰, 4s⁰

(d) all of the above

(d) 5

(b) Actinides

(d) Ce³⁺, Eu³⁺, Yb³⁺

(a) Thorium

(b) Calcium carbonate

Oxidation state of Manganese in

(i) MnO₄^2- is +6 (ii) MnO₄^- is +7

Potassium permanganate is used :

• as an antiseptic.
• as a powerful oxidising agent in laboratory and industry.
• in detection of unsaturation in organic compounds in laboratory. (Baeyer's reagent, alkaline KMnO₄).
• for detecting halides in qualitative analysis.
• in volumetric analysis for the estimation of H₂O₂, FeSO₄

(a) Sc³⁺ salts are colourless :

• The electronic configuration of ₂₁Sc [Ar] 3d¹4s² and Sc³⁺ [Ar] d°.
• Since there are no unpaired electrons in 3d subshell, d → d transition is not possible.
• Therefore, Sc³⁺ ions do not absorb the radiations in the visible region. Hence salts of Sc³⁺ are colourless (or white).

(b) Ti⁴⁺ salts are colourless :

• The electronic configuration of ₂₂Ti [Ar] 3d²4s² and Ti⁴⁺ : [Ar] d°
• Since there are no unpaired electrons in 3d subshell, d → d transition is not possible.
• Therefore, Ti⁴⁺ ions do not absorb the radiation in visible region. Hence salts of T⁴⁺ are colourless.

(c) V⁵⁺ salts are colourless :

• The electronic configuration of ₂₃V : [Ar] 3d³4s² and V⁵⁺ : [Ar] 3d°
• Since there are no unpaired electrons in 3d-subshell, d → d transition is not possible.
• Therefore, V⁵⁺ ions do not absorb the radiations in the visible region. Hence, V⁵⁺ salts are colourless.

Steps in manufacture of potassium dichromite from chromite ore are :

• Concentration of chromite ore.
• Conversion of chromite ore into sodium chromate (Na₂CrO₄).
• Conversion of Na₂CrO₄ into sodium dichromate (Na₂Cr₂O₇).
• Conversion of Na₂Cr₂O₇ into K₂Cr₂O₇.

2KMnO₄ + 5H₂C₂O₄ + 3H₂SO₄ → 2MnSO₄ + K₂SO₄ + 10CO₂ + 8H₂O

K₂Cr₂O₇ + 6Kl + 7H₂SO₄ → 4K₂SO₄ + Cr₂(SO₄)₃ + 7H₂O + 3I₂

Plutonium : +3 to +7

Cerium : +3, +4

Manganese : +2, +4, +6, +7

Europium : +2, 34

(a) Chromium (₂₄Cr) has electronic configuration,

₂₄Cr (Expected) : 1s²2s²2p⁶3s²3p⁶3d⁴4s²

(Observed) : 1s²2s²2p⁶3s²3p⁶3d⁵4s¹

Explanation :

• The energy difference between 3d- and 4s-orbitals is very low.
• d-orbitals being degenerate, they acquire more stability when they are half-filled (3d).
• Therefore, there arises a transfer of one electron from 4s-orbital to 3d-orbital in Cr giving more stable half-filled orbital. Hence, the configuration of Cr is [Ar] 3d⁵4s¹ and not [Ar] 3d⁴4s².

(b) Copper (₂₉Cu) has electronic configuration,

₂₉Cu (Expected) : 1s²2s²2p⁶3s²3p⁶3d⁹4s²

(Observed) : 1s²2s²2p⁶3s²3p⁶3d¹⁰4s¹

Explanation :

• The energy difference between 3d- and 4s-orbitals is very low.
• d-orbitals being degenerate, they acquire more stability when they are completely filled.
• Therefore, there arises a transfer of one electron from 4s-orbital to 3d-orbital in Cu giving completely filled more stable d-orbital.
• Hence, the configuration of Cu is [Ar] 3d¹⁰4s¹ and not [Ar] 3d⁹4s².

Nobelium has the electronic configuration

₁₀₂No : [Rn] 5f¹⁴6d⁰7s²

No²⁺ : [Rn] 5f¹⁴6d⁰

Since the 4f subshell is completely filled and 6d⁰ is empty, +2 oxidation state is the stable oxidation state.

Other actinoids in +2 oxidation state are not as stable due to incomplete 4f subshell.

Ce⁴ undergoes hydrolysis as, Ce⁴⁺ + 2H₂O -> Ce(OH)⁴ + 4H⁺.

Due to the presence of H⁺ in the solution, the solution is acidic.

Hence, the solution of Ce(IV) is acidic in nature.

• The shielding effect is a mechanism where the inner shell electrons in an atom screen protect the outermost electron from nuclear attraction,
• The magnitude of shielding effect depends upon the number of inner electrons.

The 90th element thorium has electronic configuration, [Rn] 6d²7s². Since it has 2 unpaired electrons it is paramagnetic.

• Atomic radii of the elements of the transition series decrease gradually from left to right.
• As we move across a transition series from left to right, the nuclear charge increases by one unit at a time.
• The last filled electron enters a penultimate (n - 1)d subshell. However, d orbitals in an atom are less penetrating or more diffused and, therefore d electrons offer smaller screening effects.
• The result is that effective nuclear charge also increases as the atomic number increases along with a transition series.
• Hence, the atomic radii gradually decrease across a transition series from left to right.
• The decrease in atomic radii is less. There is slight increase in atomic radii of last two elements Cu and Zn.

There are three zones of temperature in the Blast furnace in which three main chemical reactions take place.

(a) Zone of combustion : This is 5 - 10 m from the bottom. The hot air blown through the tuyers, oxidises coke to CO which is an exothermic reaction, due to which the temperature of furnace rises.

C + \(\frac{1}{2}\)O₂ → CO ΔH = —220 kJ

Some part of CO dissociates to give finely divided carbon and O₂.

2CO → 2C + O₂

The hot gases with CO rise up in the furnace and heats the charge coming down. CO acts as a fuel as well as a reducing agent.

(b) Zone of reduction (22-25 m near the top) : At about 900 K, CO reduces Fe₂O₃ to spongy (or porous) iron.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Carbon also reduces partially Fe₂O₃ to Fe.

Fe₂O₃ + 3C → 2Fe + 3CO

 (c) Zone of slag formation (20 m unit) : At 1200 K limestone, CaCO₃ in the charge, decomposes and forms a basic flux CaO which further reacts at 1500 K with gangue (SiO₂, Al₂O₃) and forms a slag of CaSiO3 and Ca₃AlO₃.

CaCO₃ → CaO + CO₂

CaO + SiO₂ → CaSiO₃

12CaO + 2Al₂O₃ → 4Ca₃AlO₃ + 3O₂

The slag is removed from the bottom of the furnace through an outlet.

(d) Zone of fusion (15 m ht): The impurities in ore like MnO₂ and Ca₃(PO₄)₂ are reduced to Mn and P while SiO₂ is reduced in Si. The spongy iron moving down in the furnace melts in the fusion zone and dissolves the impurities like C, Si, Mn, phosphorus and sulphure. The molten iron collects at the bottom of furnace. The lighter slag floats on the molten iron and prevents its oxidation.

The molten iron is removed and cooled in moulds. It is called pig iron or cast iron. It contains about 4 % carbon.

The electronic configuration of Fe²⁺ and Fe³⁺ :

Fe²⁺: 1s²2s²2p⁶3s²3p⁶3d⁶

Fe³⁺: 1s²2s²2p⁶3s²3p⁶3d⁵

Due to loss of two electrons from the 4s-orbital and one electron from 3d-orbital, iron attains 3+ oxidation state.

Since in Fe³⁺, the 3d-orbital is half filled, it gets extra stability, hence Fe³⁺ is more stable than Fe²⁺.

Similarity :

• They are placed between s-block and p-block of the periodic table.
• All elements are metals showing metallic characters.
• Some are paramagnetic.
• Most of them give coloured compounds.
• They have catalytic properties.
• They form complexes.

Differences :

• In 4d and 5d series lanthanide and actinoid contraction is observed. In 3d series atomic size changes are less marked.
• 4d and 5d elements have high coordination numbers compared to 3d elements.
• 4d and 5d series have similar properties whereas 3d series have different properties.
• Although most properties exhibited by d block elements are similar, the elements of the first row differ from second and third rows in the stabilization of higher oxidation states in their compounds.

• The ionisation enthalpies of transition elements are quite high and lie between those of s-block and p-block elements. This is because the nuclear charge and atomic radii of transition elements lie between those of s-block and p-block elements.
• As atomic number of transition elements increases along the period and along the group, first ionisation enthalpy increases even though the increase is not regular.
• If IE₁, IE₂ and IE₃ are the first, second and third ionisation enthalpies of the transition elements, then IE₁ < IE₂ < IE₃.
• In the transition elements, the added last differentiating electron enters into (n - 1) d-orbital and shields the valence electrons from the nuclear attraction. This gives rise to the screening effect of (n -1) d electrons.
• Due to this screening effect of (n - 1) d electrons, the ionisation enthalpy increases slowly and the increase is not very regular.

Diamagnetic substances : When a magnetic field is applied, substances which are repelled by the magnetic fields are called diamagnetic substances.

Paramagnetic substances : When a magnetic field is applied, substances which are attracted towards the applied magnetic field are called paramagnetic substances.

Examples :

• Gadolinium and lutetium show different ground-state electronic configurations because the 5d and 4f-orbitals are near to the same energy due to which the next electron goes in 5d-orbital instead of 4f-orbital.
• This retains the extra stability achieved when the 4f-orbital is half-filled and completely filled respectively. Thus, the 5d-orbital contains one electron in the case of gadolinium and lutetium.

The various steps and principles involved in the extraction of pure metals from their ores are as follows :

• Concentration of ores in which impurities (gangue) are removed.
• Conversion of ores into oxides or other reducible compounds of metals.
• Reduction of ores to obtain crude metals.
• Refining of metals giving pure metals.

• The most stable oxidation state of lanthanoids is +3.
• Hence, Ce⁴⁺ (cerium) and Tb⁴⁺ (terbium) tend to get +3 oxidation state which is more stable.
• Since they get reduced by accepting electron, they are good oxidising agents in +4 oxidation state.

• The most stable oxidation state of lanthanoids is +3.
• Hence, Eu²⁺ and Yb²⁺ tend to get +3 oxidation states by losing one electron.
• Since they get oxidised, they are good reducing agents in + 2 oxidation state.