NCERT Grade 12-The P Block Elements-Questions

NCERT Solutions for Class 12 Chemistry

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The P Block Elements

1.     Why are pentahalides more covalent than trihalides?

2.     Why is BiH3 the strongest reducing agent amongst all the hydrides of Group 15 elements?

3.     Why is N2 less reactive at room temperature?

4.     Mention the conditions required to maximize the yield of ammonia.

5.     How does ammonia react with a solution of Cu2+?

6.     What is the covalence of nitrogen in N2O5?

7.     Bond angle in PH4+ is higher than that in PH3. Why?

8.     What happens when white phosphorus is heated with concentrated NaOH solution in an inert atmosphere of CO2?

9.    Write a balanced equation for the hydrolytic reaction of PClin heavy water.

10.  What happens when PClis heated?

11.   What is the basicity of H3PO4?

12.  What happens when H3PO3 is heated?

13.  List the important sources of sulphur.

14.  Write the order of thermal stability of the hydrides of Group 16 elements.

15.  Why is H2O a liquid and H2O a gas?

16.  Which of the following does not react with oxygen directly? Zn, Ti, Pt, Fe

17.  Complete the following reactions:

18.  Why does O3 act as a powerful oxidizing agent?

19.  How is O3 estimated quantitatively?

20.  What happens when sulphur dioxide is passed through an aqueous solution of Fe(III) salt?

21.  Comment on the nature of two S-O bonds formed in SO2 molecule. Are the two S-O bonds in this molecule equal?

22.  How is the presence of SO2 detected?

23.  Mention three areas in which H2SO4 plays an important role.

24.  Write the conditions to maximize the yield of H2SO4 by Contact process.

25.  Why is Ka2 << Ka1for H2SO4 in water?

26.  Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy, compare the oxidising power of F2 and Cl2.

27.  Give two examples to show the anomalous behaviour of fluorine.

28.  Sea is the greatest source of some halogens. Comment.

29.  Give the reason for bleaching action of C12.

30.  Name two poisonous gases which can be prepared from chlorine gas.

31.  Why is ICl more reactive than I2?

32.  Why is helium used in diving apparatus?

33.  Balance the following equation: XeF6 + H2O → XeO2F2 + HF

34.  Why has it been difficult to study the chemistry of radon?

35.  Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.

36.  Why does the reactivity of nitrogen differ from phosphorus?

37.  Discuss the trends in chemical reactivity of group 15 elements.

38.  Why does NX3 form hydrogen bond but PH3 does not?

39.  How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.

40.  How is ammonia manufactured industrially?

41.  Illustrate how copper metal can give different products on reaction with HNO3.

42.  Give the resonating structures of NOand N2O5.

43.  The HNH angle value is higher than HPH, HAsH and HSbH angles. Why? [Hint: Can be explained on the basis of sp3 hybridisation in NH3 and only s-p bonding between hydrogen and other elements of the group].

44.  Why does R3P = O exist but R3N = O does not (R = alkyl group)?

45.  Explain why NH3 is basic while BiH3 is only feebly basic.

46.  Nitrogen exists as diatomic molecule and phosphorus as P4. Why?

47.  Write main differences between the properties of white phosphorus and red phosphorus.

48.  Why does nitrogen show catenation properties less than phosphorus?

49.  Give the disproportionation reaction of H3PO3.

50.  Can PClact as an oxidising as well as a reducing agent? Justify.

51.  Justify the placement of O, S, Se, Te and Po in the same group of the periodic table in terms of electronic configuration, oxidation state and hydride formation.

52.  Why is dioxygen a gas but sulphur a solid?

53.  Knowing the electron gain enthalpy values for O → O– and O → O2- as -141 and 702kJ mol-1 respectively, how can you account for the formation of a large number of oxides having O2- species and not O?

(Hint: Consider lattice energy factor in the formation of compounds).

54.  Which aerosols deplete ozone?

55.  Describe the manufacture of H2SO4 by contact process?

56.  How SO2 is an air pollutant?

57.  Why are halogens strong oxidising agents?

58.  Explain why fluorine forms only one oxoacid, HOF.

59.  Explain why inspite of nearly the same electronegativity, oxygen forms hydrogen bonding while chlorine does not.

60.  Write two uses of ClO2.

61.  Why are halogens coloured?

62.  Write the reactions of F2 and Clwith water.

63.  How can you prepare Cl2 from HCl and HCl from Cl2? Write reactions only.

64.  What inspired N. Bartlett for carrying out reaction between Xe and PtF6?

65.  What are the oxidation states of phosphorus in the following:

(i) H3PO3

(ii) PCl3

(iii) Ca3P2

(iv) Na3PO4

(v) POF3?

66.  Write balanced equations for the following:

(i) NaCl is heated with sulphuric acid in the presence of MnO2.

(ii) Chlorine gas is passed into a solution of NaI in water.

67.  How are xenon fluorides XeF2, XeF4 and XeF6 obtained?

68.  With what neutral molecule is ClO isoelectronic? Is that molecule a Lewis base?

69.  How are XeFand XeOFprepared?

70.  Arrange the following in the order of property indicated for each set:

(i) F2, Cl2, Br2, I2 increasing bond dissociation enthalpy.

(ii) HF, HCl, HBr, HI – increasing acid strength.

(iii) NH3, PH3, AsH3, SbH3, BiH3 – increasing base strength.

71.  Which one of the following does not exist?

(i) XeOF4

(ii) NeF2

(iii) XeF2

(iv) XeF6

72.  Give the formula and describe the structure of a noble gas species which is isostructural with:

73.  Why do noble gases have comparatively large atomic sizes?

74.  List the uses of Neon and argon gases.

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