CBSE Class 12 Chemistry P Block Elements Worksheet

The p-Block Elements 

3. Black phosphorus: It has two forms- α-black phosphorus and β-black phosphorus. α-black

phosphorus is formed when red phosphorus is heated in a sealed tube at 803K. It does not oxidise in air. β-Black phosphorus is prepared by heating white phosphorus at 473K under high pressure. It does not burn in air up to 673K.

Phosphine (PH₃)

Preparation: It is prepared by the reaction of calcium phosphide with water or dilute HCl.

Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃ Ca3P₂ + 6HCl → 3CaCl₂ + 2PH₃

 

In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO₂.

 

Properties: It is a colourless gas with rotten fishy smell and is highly poisonous. It is slightly soluble in water. The solution of PH3 in water decomposes in presence of light giving red phosphorus and H2. When absorbed in copper sulphate or mercuric chloride solution, the corresponding phosphides are obtained.

 

3CuSO₄ + 2PH₃ → Cu₃P₂ + 3H₂SO₄

3HgCl₂ + 2PH₃ →→Hg₃ P₂ + 6HCl

 

Like NH₃, Phosphine is weakly basic and gives phosphonium compounds with acids.

PH₃ + HBr → PH4Br

Uses: Phosphine is technically used to produce Holme’s signal. Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea. The gases evolved burn and serve as a signal. It is also used in smoke screens.

Phosphorus Halides Phosphorus forms two types of halides- PX₃ and PX₅ Phosphorus trichloride (PCl₃)

Structure:

In gaseous and liquid phases, it has a trigonal bipyramidal structure. The three equatorial P–Cl bonds are equivalent, while the two axial bonds are longer than equatorial bonds. This is due to the fact that the axial bond pairs suffer more repulsion as compared to equatorial bond pairs.

 

In the solid state it exists as an ionic solid, [PCl₄]⁺[PCl₆]- in which the cation, [PCl₄] ⁺ is tetrahedral and the anion, [PCl₆] ^- is octahedral.

P - BLOCK ELEMENTS

1.Q.Why does NO₂ dimerise?

2.Q.Give chemical reactions involved in brown ring test to confirm nitrates.

3. Q.Give the structure of nitric acid.

4. Q.Give equations in each step of oswald's process

5.Q.Give flow chart for preparation of ammonia by Haber's process.

6.Q.Explain preparation of nitrogen.

7.Q. Why do chromium and aluminium not react with the most oxidizing agent?

8.Q. Name the oxides of nitrogen and give oxidation number of each oxide.

9.Q. Give conditions which favors formation of ammonia as it is a reversible reaction.

10.Q. Draw the structures of white phosphorus and red phosphorus. Which one of these two types of phosphorus is more reactive and why?

11.Q.Whichoxoacids of phosphorus are reducing in nature?

12.Q.Why is phosphorus acid diprotic and phosphoric acid triproticinpite 3 hydrogens in both?

13.Q.Give the structure of oxy acids of phosphorus and list the anions formed.

14.Q.Why does PCl₃ fume in moisture?

15 Q.Show that PH3 is basic in nature.

16 Q.Give reason that NCl₅ is not formed but PCl₅ is formed.

.17.Show that hydrogen peroxide behaves both as an oxidizing and reducing agent.

18.Q.What is oleum? Draw its structure.

19.Q.What happens when sulphur is passed through conc. H₂SO₄ solution and SO₂ is passed through an aqueous solution of Fe(III) salt?

20. Q.Whyare halogens coloured?

I. Account for the following

1. Ammonia has higher boiling point than Phosphine.

2. Bi(V) is a strong oxidizing agent than Sb (V)

3. + 3 oxidation state becomes more and more stable from As to Bi in the group

4. The stability of +3 state increases down the group in group 15 of the periodic table.

5. The +5 oxidation state becomes less stable down the group 15 of the periodic table

6. Phosphorus shows greater tendency for catenation than Nitrogen.

7. Phosphorous ,P4 is much more reactive than Nitrogen N2

8. All the bonds in the molecules of PCl5 are not equal.

9. NH3 is stronger base than PH3.

10. PH3 is weaker base than NH3

11. PH3 forms bubbles when passed slowly in water but NH3 dissolves.

12. Nitrogen does not form pentahalides.

13. Tendency to form pentahalides decreases down the group in group 15 of the periodic table

14. In solid state PCl5 exists as Ionic compound.

15. PCl4 + is likely to exist but PCl4- is likely not to exist.

16. NH3 act as ligand.( Lewis base)

17. Ammonia(NH3) has greater affinity for protons than phosphine PH3

18. In the structure of HNO3 ,the N-O bond (121pm) is shorter than N-OH bond(140pm)

19. The N – O bond in NO2- is shorter than the N – O bond in NO3-

20. NCl3 is an endothermic compound while NF3 is an exothermic one

21. Red phosphorous is less reactive than white Phosphorous

22. CN¯ ion is known but CP¯ ion is not known.

23. H3PO2 and H3PO3 act as as good reducing agents while H3PO4 does not.

24. NO2 is coloured but N2O4 is colourless.

25. NO2 dimerises to form N2O4

26. Nitric oxide becomes brown when released in air.

27. Nitric oxide is paramagnetic in gaseous state but the solid obtained on cooling it is diamagnetic

28. Bond angle in PH4 + is higher than that in PH3

29. Pentahalides of group 15 are more Covalent than trihalides

30. The first ionization energy of nitrogen is greater than oxygen.

31. H3PO3 is diprotic acid.

32. Nitrogen exists as diatomic molecule and phosphorus as P4.

33. NH3 is basic while BiH3 is only feebly basic

34. PF5 is known while NF5 is not known.

35. Sulphur vapours exhibits paramagnetism.

36. In solution of sulphuric acid in water the Ka2 << Ka1.

37. Sulphur shows greater tendency for catenation than selenium

38. Sulphur has greater tendency for catenation than oxygen.

39. H2O is a liquid while H2S is a gas

40. H2S is less acidic than H2Te.

41. The negative value of electron gain enthalpy of oxygen atom is less than that of sulphur

42. SF6 is much less reactive than SF4

43. All the bonds in the molecules of SF4 are not equal

44. SF6 is kinetically an inert substance.

45. H2S is more acidic than H2O.

45. H2S is more acidic than H2O

46. OF6 is not known.

47. SF4 is easily hydrolysed,SF6 is not easily hydrolysed

48. OF2 should be called oxygen fluoride and not fluorine oxide

49. Dioxygen is a gas but Sulphur is a solid

50. Oxygen molecule has formula O2 while Sulphur S8

51. Oxygen generally exhibit oxidation state of –2 only whereas other members of the family exhibit +2, +4, +6 oxidation states also.

52. H2S acts as only reducing agent but SO2 acts as a reducing as well as an oxidizing agent.

53. Inspite of similar electronegativity, oxygen forms hydrogen bonding while chlorine does not.

54. The increasing order of acidic strength of HX varies in the order H2O < H2S < H2Se < H2Te.

55. SCl6 is not known but SF6 is known.

56. Ozone (O3) act as a powerful oxidising agent.

57. Ozone is thermodynamically less stable than oxygen.

58. Fluorine does not exhibit any positive oxidation state.

59. F2 is most reactive of all the four common halogens

60. F2 is a stronger oxidising agent than Cl2

61. O2 & F2 both stabilize higher oxidation states of metals but O2 exceeds F2 in doing so.

62. When HCl reacts with finely powdered iron, it forms ferrous chloride and not ferric chloride.

63. HF has higher boiling point than HCl.

64. ICl is more reactive than Cl2.

65. Bond dissociation energy of F2 is less than Cl2

66. HI in aqueous solution is strong acid than HF.

67. The negative value of electron gain enthalpy of fluorine is less than that of Chlorine.

68. Fluorine never acts as the central atom in the polyatomic interhalogen compounds

69. ClF3 molecule has a T-shaped structure and not a trigonal planar one.

70. Fluorine forms the largest number of interhalogen compounds among halogens.

71. Halogens are coloured

72. F shows oxidation state of –1 only whereas other halogens exhibit +1, +3, +5, +7 Ox. states also.

73. ClF3 exists but FCl3 does not.

74. Halogens are strong oxidizing agent

75. Most of the reactions of fluorine are exothermic

76. Fluorine forms only one oxoacid, HOF.

77. The acidic strength of oxoacids of halogens varies in the order HOF>HOCl>HOBr>HOI.

78. The acidic strength of oxoacids of halogens varies in the order: HClO4> HClO3> HClO2> HClO

79. Chlorine is a powerful bleaching agent

80. Metal fluorides are more ionic than its chlorides.

81. Perchloric acid is stonger than sulphuric acid

82. The acidic strength decreases in the order HCl > H2S > PH3

83. Helium is used in diving apparatus

84. XeF2 has a linear structure & not a bent angular structure

85. Of the noble gases only Xenon is known to form real chemical compounds

86. No Chemical compound of helium is known.

87. Xe does not forms compounds such as XeF3 and XeF5

88. Helium is used for inflating aeroplane tyres.

89. Noble gases are mostly chemically inert.

90. Structures of Xenon Flourides cannot be explained on the basis of valence bond approach

Important Questions for NCERT Class 12 Chemistry The p Block Elements

Question. Identify the incorrect statement related to PCl5 from the following :
(a) PCl₅ molecule is non-reactive.
(b) Three equatorial P – Cl bonds make an angle of 120° with each other.
(c) Two axial P – Cl bonds make an angle of 180° with each other.
(d) Axial P – Cl bonds are longer than equatorial P – Cl bonds.

Question. PCl₃ reacts with water to form
(a) PH₃
(b) H₃PO₃, HCl
(c) POCl₃
(d) H₃PO₄

Question. Which of the following oxoacids of phosphorus has strongest reducing property?
(a) H₄P₂O₇
(b) H₃PO₃
(c) H₃PO₂
(d) H₃PO₄

Question. Which is the correct statement for the given acids?
(a) Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid.
(b) Phosphinic acid is a diprotic acid while phosphonic acid is a monoprotic acid.
(c) Both are diprotic acids.
(d) Both are triprotic acids. 

Question. Strong reducing behaviour of H₃PO₂ is due to
(a) high electron gain enthalpy of phosphorus
(b) high oxidation state of phosphorus
(c) presence of two —OH groups and one P—H bond
(d) presence of one —OH group and two P—H bonds. 

Question. Which of the following statements is not valid for oxoacids of phosphorus?
(a) Orthophosphoric acid is used in the manufacture of triple superphosphate.
(b) Hypophosphorous acid is a diprotic acid.
(c) All oxoacids contain tetrahedral four coordinated phosphorus.
(d) All oxoacids contain atleast one P O unit and one P—OH group.

Question. Oxidation states of P in H₄P₂O₅, H₄P₂O₆, H₄P₂O₇ are respectively
(a) +3, +5, +4
(b) +5, +3, +4
(c) +5, +4, +3
(d) +3, +4, +5

Question. How many bridging oxygen atoms are present in P₄O₁₀?
(a) 6
(b) 4
(c) 2
(d) 5

Question. H₃PO₂ is the molecular formula of an acid of phosphorus. Its name and basicity respectively are
(a) phosphorous acid and two
(b) hypophosphorous acid and two
(c) hypophosphorous acid and one
(d) hypophosphoric acid and two. 

Question. Which one of the following substance is used in the laboratory for fast drying of neutral gases?
(a) Phosphorus pentoxide
(b) Active charcoal
(c) Anhydrous calcium chloride
(d) Na₃PO₄ 

Question. P₂O₅ is heated with water to give
(a) hypophosphorous acid
(b) phosphorous acid
(c) hypophosphoric acid
(d) orthophosphoric acid. 

Question. Basicity of orthophosphoric acid is
(a) 2
(b) 3
(c) 4
(d) 5 

Question. When orthophosphoric acid is heated to 600°C, the product formed is
(a) PH₃
(b) P₂O₅
(c) H₃PO₃
(d) HPO₃

Question. Which is the correct thermal stability order for H2E (E = O, S, Se, Te and Po) ?
(a) H₂Se < H₂Te < H₂Po < H₂O < H₂S
(b) H₂S < H₂O < H₂Se < H₂Te <H₂Po
(c) H₂O < H₂S < H₂Se <H₂Te < H₂Po
(d) H₂Po < H₂Te < H₂Se < H₂S < H₂O 

Question. Acidity of diprotic acids in aqueous solutions increases in the order
(a) H₂S < H₂Se < H₂Te
(b)H₂Se <H₂S < H₂Te
(c) H₂Te < H₂S < H₂Se
(d) H₂Se <H₂Te < H₂S

Question. Which of the following bonds has the highest energy?
(a) S–S
(b) O–O
(c) Se–Se
(d) Te–Te

Question. Which of the following does not give oxygen on heating?
(a) K₂Cr₂O₇
(b) (NH₄)2Cr₂O₇
(c) KClO₃
(d) Zn(ClO₃)₂

ONE MARK QUESTIONS

1.Why does NO₂ dimerise?

2.Fluorine does not exhibit any positive oxidation state. Why?

3.What happens when H₃PO₃ is heated?

4.Name a compound in which chlorine displays ‘+7’ oxidation number.

5.On heating Cu turnings with conc. HNO₃, a brown coloured gas is evolved which on cooling dimerises. Identify the gas.

TWO MARKQUESTIONS

1. Explain why

a) Noble gases form compounds with oxygen and fluorine only.

b) Unlike phosphorous, nitrogen has no tendency for catenation.

2.Complete the following reactions:

a) Zn + HNO₃(conc.) →

b) Cl₂ + NaOH (hot, Con) →

3.Give equations for the manufacture of a) Ammonia from nitrogen b) Nitric acid from ammonia

THREE MARKQUESTIONS

1.Arrange the following in order of the property mentioned.

a) HF, HCl, HBr, HI (increasing acid strength)

b) NH₃, PH₃, AsH₃, SbH₃ (increasing basic strength)

c) HOCl, HOClO, HOClO₃ (increasing oxidizing power) 

2.What are interhalogen compounds? How are they prepared? Why are they more reactive than molecular halogens?

3.Explain why

a) H₂S is gas while water is liquid at room temperature.

b) Helium is used in diving apparatus.

c) Iron dissolves in HCl to form FeCl₂ and not FeCl₃.

FIVE MARKQUESTIONS

1. a) Account for the following :
i) Bond angle in NH₄⁺ is greater than that in NH3.
ii) Reducing character decreases from SO₂ to TeO₂.
iii) HClO₄ is a stronger acid than HClO.
(b) Draw the structures of the following :
i) H₂S₂O₈
ii) XeOF₄

2. a) Complete the following chemical equation:
i) S₈ ⁺ HNO₃(conc.) →
ii) P₄⁺ NaOH + H₂O →
b) Explain the following observations:
i) Sulphur in vapour state exhibits paramagnetic behavior.
ii) The stability of +3 state increases down the group in group 15 of the periodic table.
iii) XeF₂ has a linear shape and not a bent structure. 
 

VALUE BASED QUESTION
1. Mark attended a seminar on the conservation of ozone layer. He came to know that freons are the compounds which are upsetting the ozone balance. So he decided to minimize the use of air conditioner.
a) What the function of ozone layer?
b) What is the value shown in the above paragraph?
c) Why does O₃ act as a powerful oxidizing reagent?
d) Besides freons, which other compounds are responsible for depletion of ozone layer?
 

Important Questions for NCERT Class 12 Chemistry The p Block Elements

Question. The ion or group detected by K₂[HgI₄] is :

(a) NO (b) Cl– 
(c) NH^2–
(d) NH⁴⁺

Answer  D

Question. Which gas cannot be collected over water ?
(a) O₂
(b) PH₃ 
(c) N₂
(d) SO₂

Answer  D

Question. The correct order of increasing oxidising power is :
(a) Cl₂ < Br₂ < F₂ < I₂ 
(b) F₂ < Br₂ < Cl₂ < I₂
(c) F₂ > Br₂ > Cl₂ > I₂
(d) I₂ > Br₂ > Cl₂ > F₂

Answer  D

Question. H₂S does not produce metallic sulphide with :
(a) CuCl₂
(b) COCl₂ 
(c) CdCl₂
(d) ZnCl₂

Answer  B

Question. The correct order of acid strength of oxyacids is: 
(a) HClO > HClO₂ > HClO₃ > HClO₄
(b) HClO ₂ > HClO ₃ > HClO > HClO₄
(c) HClO₄ > HClO₃ > HClO₂ > HClO
(d) HClO₃ > HClO₄ > HClO > HClO₂

Answer  C

Question. Chlorine acts as a bleaching agent only in presence of: 
(a) Sunlight
(b) Moisture
(c) Dry air
(d) Pure oxygen

Answer  B

Question. The laughing gas is: 
(a) NO
(b) N₂O
(c) N₂O₄
(d) N₂O₅

Answer  B

Question. The correct decreasing order of basic strength is:
(a) AsH₃ > SbH₃ > PH₃ > NH₃ 
(b) SbH₃ > AsH₃ > PH₃ > NH₃
(c) NH₃ > PH₃ > AsH₃ > SbH₃
(d) PH₃ > AsH₃ > SbH₃ > NH₃

Answer    C

Question. Iodide of Millon's base is : 
(a) HIO₃
(b) K₂HgI₄
(c) NH₂HgO.HgI
(d) Hg(NH₂ )I

Answer  C

Question. Which of the following is not the characteristic of interhalogen compounds? 
(a) they are covalent
(b) more reactive than halogens
(c) have low B.P. and high volatile
(d) quite unstable but not explosive

Answer  C

Question. Hypo on treatment with iodine produces :
(a) H₂S
(b) Na₂SO₄ 
(c) Na₂SO₃
(d) Na₂S₄O₆

Answer  D

Question. The tribasic acid is : 
(a) H₃PO₄
(b) H₃PO₃
(c) H₃PO₂
(d) HPO₃

Answer  A

Question. The strongest oxidising agent is : 
(a) F₂
(b) Cl₂
(c) I₂
(d) Br₂

Answer  A

Question. The correct order of solubility in water for He,Ne, Ar, Kr, Xe is 
(a) He > Ne > Ar > Kr > Xe
(b) Xe > Kr > Ar > Ne > He
(c) Ne > Ar > Kr > He > Xe
(d) Ar > Ne > He > Kr > Xe

Answer  B

Question. Which of the following compound is a tribasic acid? 
(a) H₃PO₂
(b) H₃PO₄
(c) H₃PO₃
(d) H₄P₂O₇

Answer  B