CBSE Class 12 Chemistry d and f block elements Type MLL Questions Answers

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Chapter: d and f- block elements

Type: MLL

Explain Why? / How would you account for the following: [1 mark each?]

1. Transition metals are less reactive, high melting point and enthalpy of atomization.

2. Transition metals have high enthalpy of hydration.

3. Transition metals show several oxidation states.

4. Transition metals form coloured complexes.

5. Transition metals take part in catalytic reactions.

6. Why does vanadium pentaoxide act as a catalyst?

7. Transition metals are paramagnetic in nature.

8. Transition metals form complexes.

9. Transition metals have irregular E0 values.

10. The E⁰M_²⁺/M for copper is positive (0.34v) .Copper is the only metal in first series of transition elements showing this behavior, why?

11. Transition metals form alloys.

12. Transition metals form interstitial compounds.

13.Cu⁺ is unstable in aqueous solution.

14.Cu²⁺is stable in aqueous solution.

15. Zr and Hf exhibit almost same radii and properties.

16. The d¹ configuration is generally unstable in ions.

17. There is a general increase in density of element from titanium (Z=22) to copper ( Z=29).

18. The lowest oxides of transition metals is basic, the highest is amphoteric or acidic.

19. Anhydrous CuSO₄ is white while hydrated Copper sulphate is blue.

20.Co^₂+ is easily oxidized to Co³⁺ in presence of strong ligand.

Two marks questions

21. (a) Why HCl cannot be used in place of sulphuric acid to acidify KMnO4 solution in volumetric analysis ?

(b) Potassium dichromate is a good oxidising agent in acidic medium, why?

22. Write the balanced ionic equations for reacting ions to represent the acidified potassium dichromate solution with:

(i) Potassium iodide solution

(ii) Acidified ferrous sulphate solution.

23. List some applications of d- block elements.

24. Describe giving reasons which one of the following pairs has the properties indicated?

(a) Fe or Cu has higher melting point.

(b) Co²⁺Or Ni²⁺ has lower magnetic moment.

25. Calculate the magnetic moment of a trivalent ion in aqueous solution whose atomic no. is

26. Define transition elements. Explain why is Zn not considered as transition element while Cu does?

27. What happens when Cu²⁺ is added to I-? Write the balanced chemical equation.

28. Write the electronic configuration of^₂₄ Cr and ²⁶Fe²⁺ .

29. Compare non transition and transition elements on the basis of their Variability of oxidation states (ii) stability of oxidation states.

30. (a) Name a transition element which does not exhibit variable oxidation state.

(b) Name three elements of d block which are not regarded as transition element.

Three Marks questions

31. Give chemical reactions for the following observations:

(i) Potassium permanganate is a good oxidizing agent in basic medium.

(ii) Inter convertibility of chromate ion and dichromate ion in aqueous solution depends Upon pH of the solution.

(iii) Potassium permanganate is thermally unstable at 513K.

32. Define lanthanide Contraction. Ce⁴⁺ is a good oxidizing agent whereas Eu²⁺, Sm²⁺ is a good reducing agent, why ?

33. (a)From element to element the actinoid contraction is greater than lanthanides contraction, why?

(b) Name the lanthanide element which forms tetra positive ions in the aqueous solution.

© The chemistry of actinoids is not as smooth as lanthanoids, why?

34. Balance the following equations:

(i) MnO₄- + S₂O₃^2- (Basic medium)

(ii) Mn_O4- + S₂O₃ ^2-+ H₂O

(iii) MnO4- + I- (in neutral or alkaline medium)

35. (a) The enthalpies of atomization of transition metals of 3d series do not follow a regular trend throughout the series.

(b) The enthalpy of atomization of zinc is lowest.

© Zn Cd Hg are soft and have low melting points.

36. Explain:

(a) The E° value for Ce⁴⁺/Ce_³⁺ is 1.74 Volt.

(b)K₂Cr₂O₇ is used as Primary Standard in volumetric analysis.

© The third ionization energy of manganese (z=25) is exceptionally high.

37. Explain:

(a)Although Cu⁺ has configuration 3 d¹⁰ 4 s⁰ (stable) and Cu2+ has configuration 3 d9 (unstable configuration) still Cu2+ compounds are more stable than Cu+.

(b) Titanium (IV) is more stable than Ti (III) or Ti (II).

© The greatest number of oxidation states are exhibited by the members in the middle of a transition series.

38. (a) Highest manganese flouride is MnF₄ whereas the highest oxide is Mn₂O₇, why?

(b) Copper can notlibrate H₂ from dilacids,why?

(c)Which of the 3d- series of transition metals exhibits largest number of oxidation states and why?

39. (a)O.S. of first transition series initially increase up to Mn and then decrease to Zn , why?

(b) Why is Cr²⁺ reducing and Mn³⁺ oxidizingwhile both have d⁴ configuration.

© Ti achieves tetrahalides while chromium forms heaxhalide, why?

40. (a)Which form of Cu is paramagnetic and why?

(b) What is the oxidation no. of Cr in Cr₂O₇²-?

41. Complete the following reaction equations:

(a) MnO₂ + KOH (aq) + O₂

(b) Fe²⁺ + MnO_4- + H⁺

(c) MnO₄- + C₂O₄ ^2- (aq) + H⁺

(d) Cr₂O₇^2- + H₂S + H⁺

(e) Cr₂O₇^2- + I- + H ⁺

42. Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing PH on a solution of potassium dichromate or Explain how the colour of K₂Cr₂O₇ solution depends on PH of the solution?

43. (a)Describe the preparation of potassium permanganate.

(b) How does the acidified permanganate solution react with (i) iron (II) ions (ii) SO₂ and (iii) oxalic acid? Write the ionic equations for the reactions.

44. Describe the oxidising action of potassium dichromate and write the ionic. 

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