D Block Elements 2 Flashcards
Why paramagnetic nature increases from Sc to Mn and then decreases?
because number of unpaired electrons increases from Sc to Mn and
then decreases.
Magnetic moment formula?
μ = √n (n + 2) BM, Where, n = number of unpaired electrons and BM = Bohr magneton (unit of
magnetic moment).
Calculate the magnetic moment of Mn2+
√35BM
Why Most of transition metals are used as catalyst
(i) because of presence of incomplete or empty d – orbitals
(ii) large surface area
(iii) variable oxidation state
(iv) ability to form complexes
e.g., Fe, Ni, V2O5, Pt, Mo, Co and used as catalyst.
Why do transition metals form coloured compounds:
They form coloured ions due to presence of incompletely filled d – orbitals
and unpaired electrons, they can undergo
d–d transition.
Why Transition metals form complexes?
due to:
(i) presence of vacant d – orbitals of suitable energy
(ii) smaller size
(iii) higher charge on cations.
Explain Interstitial compounds by Transition metals
Transition metals have voids or interstitials in which C, H, N, B etc.
can fit into, resulting in formation of interstitial compounds. They are
non – stoichiometric, e.g., steel. They are harder and less malleable
and ductile.
Why Transition metals form Alloys?
They form alloys due to similar ionic size. Metals can replace each
other in crystal lattice, e.g., brass, bronze, steel etc.
Explain the preparation of Potassium dichromate.
Potassium dichromate is prepared from chromite ore. FeO.Cr2O3
Steps
4FeOCr2O3 + 8Na2CO3 + 7O2 —→ 8Na2CrO4 + 2Fe2O3 + 8CO2
2Na2CrO4 + H2SO4 —-→ Na2Cr2O7 + Na2SO4 + H2O
Na2Cr2O7 + 2KCl ——→ K2Cr2O7 + 2NaCl
The chromates and dichromates are interconvertible in aqueous solution
depending upon pH of the solution. The oxidation state of chromium in chromate and dichromate is the same.
2CrO42– +2H+ →Cr2O72– +HO 4272
Cr2O72– +2OH- →2CrO42– +HO
Explain the structure of chromate and dichromate ions.
The chromate ion is tetrahedral.
The dichromate ion consists of two tetrahedra sharing one corner with
Cr–O–Cr bond angle of 126.
Explain the uses of K2Cr2O7
i) Potassium dichromate is used for the identification of SO2 gas.
On passing SO2 gas Orange colour of potassium dichromate gets
decolourised.
Cr2O72-+2H++2SO2 —→2Cr2(SO4)3+H2O
ii) Chromyl chloride test using pot. dichromate is used for the
identification of Cl ions.
Explain the preparation of Potassium permanganate.
Potassium permanganate is prepared from pyrolusite, MnO2
2MnO2 + 4KOH + O2 —→ 2MnO42–+ 2H2O
3MnO42–+ 4H+ →2MnO4– +MnO2 +2H2O
Laboratory preparation of KMnO4.
2Mn2++5S2O82–+8H2O→2MnO4+10SO42-+16H+
Action of heat on KMnO4.
2KMnO4 → K2MnO4 + MnO2 + O2
KMnO4 is isostructural with those of KClO4.
Isostructural chemical compounds have similar chemical structures. In this case, both KMnO4 and KClO4 form dark purple crystals.
