chemistry

EAMCET QUESTIONS FROM CHAPTER D AND F-BLOCK ELEMENTS PART-1

Problem 1: The chemical reactivity of lanthanides resemble to which other elements of the periodic table?

Solution: The chemical reactivity of the starting lanthanides resemble calcium due to similar first and second ionization energy. But latter lanthanides resemble Al due to ability of showing +3 oxidation state and similarity in I.E.

Problem 2: Enthalpies of atomization of transition elements are higher than those of alkali and alkaline earth metals. Explain.

Solution: The number of unpaired electrons in transition elements are more when compared to these in alkali and alkaline earth metals. As a result, the metallic bonds in transition metals are stronger and enthalpies of atomization are higher than those of alkali and alkaline earth metals. 

Problem 3: Explain the following:

(a) Chromium is a typical metal while mercury is a liquid metal.

(b) Zinc readily liberates H2 from cold dil. H2SO4 but not form cold conc. H2SO4.

Solution:

(a) Chromium has five unpaired electrons in its d-orbitals which make its metallic bond very strong, whereas in mercury there is no unpaired d-electrons so its metallic bond is very weak, hence it is a liquid.

(b) Since, conc. H2SO4 act as an oxidizing agent hence does not evolve H2 when it reacts with zinc.

          Zn + 2H2SO4 ————→ ZnSO4 + SO2 + H2O

Problem 4: Compare thermal stability of ZnO, CdO and HgO.

Solution: ZnO > CdO > HgO

Problem 5: Cu+ ion has 3d104s0 configuration and colourless but Cu2O is red and Cu2S is black. Explain.

Solution: Cu+ ion has 3d104s0 configuration, i.e. it has no unpaired electron hence there is no d-d transition possible and it is colourless. But Cu2O and Cu2S are coloured due to charge transfer of electrons from O2- or S2- to the vacant orbital of Cu+ ion.

Problem 6: While Cu, Ag and Au are considered as transition elements but Zn, Cd and Hg are not considered as transition elements although all the mentioned elements have complete d-orbitals. Explain.

Solution: Although Cu, Ag and Au have their d – orbitals complete in the elemental state. They do have incomplete d orbitals in their compound state. So they are included in the transition elements.

      Cu+2 = 3d9

      Au+3 = 5d8

Zn, Cd and Ag have their d-orbitals complete in their elemental state as well as compound state. So they are not included in the transition elements.

      Zn+2 = 3d10

      Hg+2 = 5d10 

Problem 7:

(i) CrO3 is an acid anhydride. Explain.

(ii) Between Na+ and Ag+ which is a stronger Lewis acid and why?

Solution:

(i) CrO3 + H2O ————→ H2CrO4, i.e CrO3 is formed by loss of one H2O molecule from chromic acid.

(ii) Between Na+ and Ag+, Ag+ is stronger Lewis acid. Because Ag+ has pseudo noble gas configuration which makes it more polarizing.

Problem 8: It is well known that alkali and alkaline earth metals displace hydrogen from dilute acids. But most of the transition elements do not behave so. Explain.

Solution: Alkali and alkaline earth metals have positive oxidation potential. But most of the transition elements have negative oxidation potentials. So they are not as good oxidizing agents as the alkali and alkaline earth metal are.