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P Block > Group 15 > Flashcards

Group 15 Flashcards

1
Q

Group 15 elements

A

Nitrogen - Phosphorous - Arsenic - Antimony - Bismuth

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2
Q

Comment on metallic nature of group 15 elements

A
  1. N, P are non-metals
  2. As, Sb are metalloids
  3. Bi is a metal
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3
Q

Occurrence of Nitrogen

A
  1. Nitrogen comprises around 78% of air
  2. It is found in NaNO3 and KNO3
  3. It is also found as proteins in plants and animals
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4
Q

Chile Saltpetre

A

NaNO3

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5
Q

Indian Saltpetre

A

KNO3

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6
Q

Occurrence of Phosphorous

A
  1. Occurs mainly as minerals of the apatite family which are the main components of phosphate rocks
  2. Essential part of plant and animal matter - it exists in bones as well in cells
  3. Phosphoproteins occur in milk and eggs
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7
Q

Occurrence of As, Sb, Bi

A

Mainly occur in sulphide minerals

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8
Q

Apatite family

A

Ca9(PO4)6.CaX2

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9
Q

Electronic Configuration of group 15

A

ns2np3

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10
Q

Discuss atomic size trend

A

It increases down the group due to increase in number of shells.
From N to P, there is expected increase but from As to Bi, there is only a small increase because of completely filled d and f orbitals

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11
Q

Discuss ionization enthalpy trend

A

It decreases down the group due to increase in number of shells.
It must be noted that group 15 elements have a much higher IE than the expected increase because of extra stability of half filled orbital (p3)

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12
Q

Discuss electronegativity trend

A

It decreases with increasing size. But amongst the heavier elements, the difference is not very big

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13
Q

Physical properties of group 15 elements

A
  1. N is a diatomic gas while the rest are polyatomic solids
  2. BP increases down the group
  3. MP increases from N to As and then decreases
  4. Except N, all elements show allotropy
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14
Q

Why does metallic character increase down the group?

A

Because of increase in atomic size and decrease in ionization enthalpy

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15
Q

Discuss variations in OS

A
  1. This group shows mainly -3, +3 and +5
  2. Stability of -3 decreases down the group due to increase in metallic character and size - Bi does not form compounds in this OS
  3. Stability of +5 decreases down the group due to inert pair effect - BiF5 is the only stable Bi compound in this OS state
  4. +3 increases down the group
  5. N also shows +1, +2 and +4 with oxygen
  6. P also shows +1, +4 in some oxoacids
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16
Q

Discuss disproportionation reactions in group 15 elements.

A
  1. In N, all OS between +1, +4 disproportionate to -3 and +5 in acid mediums
  2. P also disproportionates into +5 and -3 in acid and alkali solutions
  3. In As, Sb and Bi, +3 shows more stability wrt disproportionation
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17
Q

Anomalous properties of N

A
  1. It can form p(pi)-p(pi) bonds with itself and other elements of high electronegativity and small size like C and O
  2. It exists as a triple bonded diatomic molecule
  3. It cannot expand its covalence beyond 4 due to the absence of d orbitals
  4. . It cannot d(pi)-p(pi) or d(pi)-d(pi) like the other elements in this group
  5. The N-N bond is weaker than the P-P bond because of high repulsion of non-bonding electrons owing to the small bond length
  6. Has weak catenation tendency
  7. Has high bond enthalpy
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18
Q

What kind of bonds do the group 15 elements form with themselves?

A
  1. N has a triple bond relationship with itself
  2. P, As, Sb form P-P, As-As, Sb-Sb single bonds
  3. Bi is bonded to itself through metallic bonding
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19
Q

Reactivity towards Hydrogen

A
  1. Forms hydrides of form EH3
  2. The hydride stability decreases down the group -> BDE decreases down the group
  3. Basicity also decreases down the group
  4. Reducing nature increases down the group
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20
Q

Reactivity towards oxygen

A
  1. Forms oxides of the form E2O3 and E2O5
  2. Acidity of these oxides decrease down the group
  3. Oxide in higher OS is more acidic than the one in lower OS
  4. E2O3 oxides: N, P are purely acidic, As and Sb are amphoteric and Bi is basic
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21
Q

Reactivity towards halogen

A
  1. Forms halides of the form EX3 and EX5
  2. Nitrogen cannot form EX5 due to absence of d orbitals
  3. All the trihalides are known to be stable except the nitrogen ones
  4. Pentahalides are more covalent than trihalides
  5. Except BiF3, all trihalides are covalent
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22
Q

Reactivity towards metals

A

All elements form compounds of the form M3E2 with -3 oxidation state

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23
Q

Why are pentahalides more covalent than the trihalides?

A

Higher the OS, more the polarizing power and hence more covalent the compound is

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24
Q

Preparation of nitrogen

A
  1. Commercially produced by liquefaction and fractional distillation of air - N2 distills out first leaving behind liquid oxygen
  2. Industrially produced by reacting NaNO2 and NH4Cl - this also produces small amount of HNO3 and NO which can be removed by passing the gas through aq. solution of sulphuric acid with potassium dichromate
  3. It can also be produced by thermal decomposition of ammonium dichromate - (NH4)2Cr2O7
  4. Very pure N2 is obtained by decomposition of Ba(N3)2
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25
Q

Physical Properties of nitrogen

A
  1. Colorless, tasteless, odorless gas
  2. Non toxic
  3. Has very low solubility
  4. Low FP, MP
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26
Q

Solubility of nitrogen

A

23.2 cm3/L

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27
Q

Isotopes of nitrogen

A

N(14) and N(15)

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28
Q

Reactivity of nitrogen

A
  1. Nitrogen is extremely inert due to high bond enthalpy of the triple bonded diatomic molecule
  2. But as temperature increases, reactivity also increases
  3. At high temperatures, it directly combines with metals to form nitrides - ionic with metals and covalent with non-metals
  4. At 2000K, it reacts with oxygen to form NO
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29
Q

Haber’s process

A

N2 reacts with H2 at 773 K, in presence of a catalyst to form NH3
N2 + 3H2 = 2NH3

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30
Q

Conditions for Haber’s process

A
  1. According to Le Chatelier, high pressure would favor formation of products in this case - ideally, 200 atm is used
  2. A temperature of ~ 700 K
  3. A catalyst - iron oxide with traces of Al2O3 and K2O
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31
Q

What catalyst was used earlier in Haber’s process

A

Fe with Mo as a promoter

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32
Q

Preparation of ammonia

A
  1. It exists in air and soil due to decomposition of urea
    NH2CONH2 + H2O = (NH4)2CO3 = NH3 + H2O + CO2
  2. For small scale production, ammonium salts are decomposed using caustic soda or limewater
  3. On a large scale, Haber’s process is used
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33
Q

Physical Properties of ammonia

A
  1. Colorless gas with a pungent odor
  2. Has higher MP, BP than expected because of its capability to form hydrogen bonds
  3. It is trigonal pyramidal with N at the apex
  4. It has 3 bp and 1 lp
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34
Q

Chemical Properties of ammonia

A
  1. It is highly soluble in water and forms a weakly basic solution due to release of OH- ions
  2. It forms ammonium salts with acids
  3. As a weak base, it precipitates the hydroxides of many metals from their salt solution
  4. Presence of lone pair makes NH3 a Lewis base and it donates electron pair to form linkage with metal ions to form complex compounds
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35
Q

Comment on the complex compounds formed on reacting NH3 with metals

A
  1. It is used to detect presence of metal ions
  2. (Cu2+) + NH3 = [Cu(NH3)4]2+ (blue color)
  3. (Ag+) + (Cl-) = AgCl (white ppt)
  4. NH3 + AgCl = [Ag(NH3)2]Cl (colorless)
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36
Q

Preparation of N2O

A

NH4NO3 = N2O + H2O

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37
Q

Preparation of NO

A

NaNO2 + FeSO4 + H2SO4 = Fe2(SO4)3 + NaHSO4 + H2O + NO

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38
Q

Preparation of N2O3

A

2NO + N2O4 = 2N2O3

39
Q

Preparation of NO2

A

Pb(NO3)2 = PbO + NO2 + O2

40
Q

Preparation of N2O4

A

NO on cooling N2O4

41
Q

Preparation of N2O5

A

HNO3 + P4O10 = HPO3 + N2O5

42
Q

Structures of oxides of nitrogen

A

Open NCERT and go through them rn lui

43
Q

Physical appearance, state and chemical nature of N2O

A

Colorless gas, neutral

44
Q

Physical appearance, state and chemical nature of NO

A

Colorless gas, neutral

45
Q

Physical appearance, state and chemical nature of N2O3

A

Blue solid, acidic

46
Q

Physical appearance, state and chemical nature of NO2

A

Brown gas, acidic

47
Q

Physical appearance, state and chemical nature of N2O4

A

Colorless solid/liquid, acidic

48
Q

Physical appearance, state and chemical nature of N2O5

A

Colorless solid, acidic

49
Q

Why does NO2 dimerise

A

Because NO2 has an odd number of valence electrons. When it dimerizes to form N2O4, it attains an even number of electrons and is more stable

50
Q

Hyponitrous acid

51
Q

Nitrous acid

52
Q

Preparation of HNO3

A
  1. In laboratories, it is prepared by treating sodium/potassium nitrate with concentrated H2SO4 in a glass retort
    NaNO3 + H2SO4 = NaHSO4 + HNO3
  2. On a large scale, it is prepared by Ostwald’s process
53
Q

Ostwald’s process

A

Catalytic oxidation of NH3 by O2
NH3 + O2 = NO + H2O (with Pt/Rh gauge catalyst)
NO + O2 = NO2
NO2 + H2O = HNO3 + NO
This NO formed can then be recycled
The aq. HNO3 formed can be distilled up to 68% by mass
This can be taken up to 98% by dehydration with concentrated H2SO4

54
Q

Physical Properties of HNO3

A
  1. Colorless liquid
  2. Laboratory grade HNO3 contains 68% by mass
  3. Specific gravity = 1.504
  4. Planar molecule in gaseous state
55
Q

Chemical Properties of HNO3

A
  1. It is a strong acid releasing H3O+ and NO3- ions in water
  2. It is a very strong oxidizing agent and attacks most metals. The product formed depends on multiple conditions
  3. Non metals can also be oxidized
56
Q

What kind of products on oxidation of metals with HNO3?

A 
The product depends on concentration of acid, temperature and nature of the material
Cu + dil. HNO3 releases NO
Cu + conc.HNO3 releases NO2
Zn + dil. HNO3 releases N2O
Zn + conc.HNO3 releases NO2
57
Q

Brown Ring test

A

Tests for the presence of nitrates
The test depends on the ability of Fe2+ to reduce nitrates to nitric oxide which reacts with Fe2+ to form brown colored solution

58
Q

Brown ring complex

A

[Fe(H2O)5NO]2+

59
Q

Physical properties of white phosphorous

A
  1. Translucent white waxy solid
  2. Insoluble in water
  3. Soluble in CS2
  4. Glows in the dark - chemiluminescence
  5. Discrete Tetrahedral P4 molecule
60
Q

Chemical properties of white phosphorous

A
  1. It is soluble in NaOH solution and releases phosphine gas
    NaOH + P4 + H2O = PH3 + NaH2PO2
  2. Less stable because of angle strain in the molecule (60)
  3. It dissolves in air to give white dense fumes of P4O10
61
Q

How is red phosphorous prepared?

A

By heating white phosphorous in an inert atmosphere ay 573 K for several days

62
Q

Physical properties of red phosphorous

A
  1. It does not glow in the dark
  2. It is insoluble in both water and CS2
  3. Has iron grey luster
  4. Polymer made of linked P4 tetrahedra
  5. Odorless, non poisonous
  6. Much less reactive than white
63
Q

How is black phosphorous prepared?

A

By heating red phosphorous under high pressure

64
Q

Types of black phosphorous

A

Alpha black and beta black phosphorous

65
Q

Alpha black phosphorous

A
  1. Prepared by heating red phosphorous at 803 K in a sealed tube
  2. Can be sublimed in air
  3. Exists as opaque monoclinic or rhombohedral units
  4. Does not oxidize in air
66
Q

Beta black phosphorous

A
  1. Prepared by heating white phosphorous to 473 K under high pressure
  2. Does not burn in air up to 673 K
67
Q

Preparation of Phosphine

A
  1. It is prepared by treating Ca3P2 with water or dilute HCl
    Ca3P2 + HCl = CaCl2 + PH3
  2. In the laboratory, it is prepared by heating white phosphorous with NaOH and water in an inert atmosphere of CO2
68
Q

Discuss purity of PH3 prepared

A
  1. When pure, it is non inflammable
  2. But in presence of P4 or P2H4 vapors, it becomes inflammable
  3. To purify it from the impurities, it is absorbed in HI to form phosphonium iodide PH4I which on treating with KOH gives out phosphine
    PH4I + KOH = KI + H2O + PH3
69
Q

Physical properties of PH3

A
  1. Colorless gas
  2. Rotten fish smell
  3. Highly poisonous
  4. Explodes in contact with oxidizing agents like HNO3 and Cl2
  5. Slightly soluble in water
70
Q

Chemical properties of PH3

A
  1. Solution of PH3 in water decomposes in presence of light to give red P and H2
  2. When absorbed in CuSO4 or HgCl2, corresponding phosphides and acids are formed.
    CuSO4 + PH3 = Cu3P2 + H2SO4
  3. It is weakly basic and forms phosphonium compounds with acids
71
Q

Preparation of PX3

A
  1. By passing dry halogen over heated white phosphorous
    P4 + X2 = PX3
  2. By reacting white phosphorous with thionyl chloride
    P4 + SOCl2 = PCl3 + S2Cl2 + SO2
72
Q

Properties of PX3

A
  1. Colorless oily liquid
  2. Has a pyramidal shape, P is sp3 hybridized
  3. Is hydrolyzed in presence of moisture
    PCl3 + H2O = H3PO3 + HCl
  4. Reacts with compounds containing -OH group to form acid chlorides or haloalkanes
    C2H5COOH + PCl3 = C2H5COCl + H3PO3
73
Q

Preparation of PX5

A
  1. By passing an excess of dry halide over white phosphorous
    P4 + X2(excess) = PX5
  2. By reacting white phosphorous with thionyl chloride
    P4 + SOCl2 = PCl5 + SO2
74
Q

Physical properties of PX5

A
  1. Yellowish white powder
  2. In gaseous and liquid phases, it has trigonal bipyramidal structure.
  3. The 3 equatorial bonds are equivalent. The two axial bonds are longer because they face larger repulsion
  4. In solid state, it exists as [PCl4]+[PCl6]- where PCl4 is tetrahedral and PCl6 is octahedral
75
Q

Chemical properties of PX5

A
  1. In moist air, it hydrolyses to give POCl3 and then H3PO4
    PCl5 + H2O = POCl3 + HCl
    POCl3 + H2O = H3PO4 + HCl
  2. It sublimes on heating but decomposes on stronger heating giving PCl3 and Cl2
  3. It reacts with organic compounds with -OH group to give chloro derivatives
    C2H5OH + PCl5 = C2H5Cl + POCl3 + HCl
  4. PCl5 reacts with finely divided metals to give their chlorides
    Ag + PCl5 = AgCl + PCl3
76
Q

Hypo phosphorous acid

A

H3PO2

Also called phosphinic acid

77
Q

Ortho phosphorous acid

A

H3PO3

Also called phosphonic acid

78
Q

Pyro phosphorous acid

79
Q

Hypo phosphoric acid

80
Q

Ortho phosphoric acid

81
Q

Pyro phosphoric acid

82
Q

Meta phosphoric acid

83
Q

How is hypo phosphorous acid prepared

A

White P4 + alkali

84
Q

How is ortho phosphorous acid prepared

A

P2O3 + H2O

85
Q

How is pyro phosphorous acid prepared

A

PCl3 + H2O

86
Q

How is hypo phosphoric acid prepared

A

red P4 + alkali

87
Q

How is ortho phosphoric acid prepared

A

P4O10 + H2O

88
Q

How is pyro phosphoric acid prepared

A

Heat phosphoric acid

89
Q

How is meta phosphoric acid preapred

A

Phosphorous acid + Br2 and heat in a sealed tube

90
Q

Structures of oxoacids of phosphorous

A

Open NCERT and go through them rn lui

91
Q

Comment on disproportionation of oxoacids of phosphorous

A

Phosphorous acids where OS of P is +3 tend to disproportionate

92
Q

Comment on reducing nature of oxoacids of phosphorous

A

Oxoacids with P-H bond are highly reducing in nature

93
Q

Comment on ionization of oxoacids of phosphorous

A

Oxoacids with P-H bond do not ionize to give H+ and hence do not play a role in basicity.
But the oxoacids with P-OH bond are quite basic in nature and ionisable

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