Previous Year Papers

Download Solved Question Papers Free for Offline Practice and view Solutions Online.

Test Series

Take Zigya Full and Sectional Test Series. Time it out for real assessment and get your results instantly.

Test Yourself

Practice and master your preparation for a specific topic or chapter. Check you scores at the end of the test.

The d-And-f-Block Elements

Short Answer Type

241.

Assign reasons for the following:
Transition metals and their many compounds act as good catalyst.

176 Views

242.

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

172 Views

243. The E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺? Explain.

231 Views

244.

Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element.

1353 Views

245.

What may be the possible oxidation states of the transition metals with the following d electronic configurations in the ground state of their atoms: 3d³4s²,3d⁵4s² and 3d⁶4s². Indicative relative stability of oxidation states in each case.

411 Views

Long Answer Type

246. Write steps involved in the preparation of (i) Na₂CrO₄ from chromite ore and (ii) K₂MnO₄ from pyrolusite ore.

(i) Na₂CrO₄ from chromite ore: Preparation of sodium chromate : The chromite ore (FeO.Cr₂O₃) is finely powdered and mixed with sodium carbonate and quick lime and then heated to redness in a reverberatory furnace with free supply of air.
4FeO.Cr₂O₃ + O₂ -->2Fe₂O₃ +4Cr₂O₃
[4Na₂CO₃ +2Cr₂O₃ +3O₂--->4Na₂CrO₄ +4Cr2O3]x2
4FeO.Cr₂O₃ +8Na₂CO₃ +7O₂--->8Na₂CrO₄ +2Fe₂O₃ +8CO₂

The mass is then extracted with water, when sodium chromate is completely dissolved while Fe₂O₃ is left behind.

(ii) K₂MnO₄ from pyrolusite ore:
Fusion of ore with alkali in presence of air: Pyrolusite ore is fused with alkali in the presence of air when potassium manganate is obtained as green mass.

The green mass is dissolved in water to obtain aqueous solution of Potassium manganate. The insoluble impurities of sand and other metal oxides are removed by filtration.