CHEMICAL PROPERTIES OF D-BLOCK ELEMENTS AND THEIR COMPOUNDS ASSIGNMENT

QUESTIONS

1. (a) Describe the general trends in the following properties of the first series of the transition
elements:-
(i) Stability of +2-oxidation state
(ii) Formation of oxometal ions
(b) Write steps involved in the preparation of KMnO4 from K2MnO4

2.(a) What is lanthanide contraction? What effect does it have on the chemistry of the elements, which follow lanthanoids?
(b) The chemistry of actinoid elements is not so much smooth as that of lanthanoids. Justify these statements by giving some examples from the oxidation state of these elements.
(a)The size of Lanthanoids and its trivalent ion decreases from La to Lu. It is known as
lanthanoids contraction.
Cause: – It is due to poor shielding of 4f electrons.
Consequences of lanthanide contraction: – (i) Basic strength of hydroxide decreases from La(OH)3
TO Lu(OH)3. (ii) Because of similar chemical properties lanthanides are difficult to separate.
(b) Lanthanoids show limited number of oxidation states i.e. +2, +3, +4 (out of which +3 is most
common) . This is because of a large energy gap between 4f, 5d and 6s subshell. The dominant
oxidation state of actinides is also +3 but they show a number of other oxidation state also e.g. +4,
+5, and +7. This is due to small energy difference between 5f, 6d and 7s orbitals.

ANSWERS

1. (a) i-The elements of first transition series show decreasing tendency to form divalent cation
as we move left to right in the series. This trend is due to general increase in the first and second
ionization energy. The greater stability of Mn2+ is due to half filled d5 configuration and that of zinc
is due to d10 configuration.
(ii) All metal except Sc from oxide of type MO which are basic. The highest oxidation number in all
oxide, with the group number and is attain in Sc2O3 to Mn2O7. Formation of oxoanions is due to high
electro negativity and small size of oxygen atom.

(b) It takes place in two steps:-

(iii) Conversion of pyrolusite ore into potassium mangnate.
(iv) Conversion of potassium mangnate to potassium permanganate.
Following reactions take place:-
2 MnO2 + 4 KOH + O2 …….2 K2MnO4 + 2H2O
3 MnO42- +4H……………….. 2 MnO4- +MnO2 +2H2O

2. (a)The size of Lanthanoids and its trivalent ion decreases from La to Lu. It is known as lanthanoids contraction. Cause: – It is due to poor shielding of 4f electrons. Consequences of lanthanide contraction: –

(i) Basic strength of hydroxide decreases from La(OH)3
TO Lu(OH)3.

(ii) Because of similar chemical properties lanthanides are difficult to separate.
(b) Lanthanoids show limited number of oxidation states i.e. +2, +3,+4 (out of which +3 is most common) . This is because of a large energy gap between 4f, 5d and 6s subshell. The dominant oxidation state of actinides is also +3 but they show a number of other oxidation state also e.g. +4,+5, and +7. This is due to small energy difference between 5f, 6d and 7s orbitals.