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Inorganic Chemistry > P-Block Group 15-16 > Flashcards

P-Block Group 15-16 Flashcards

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1
Q

Occurence of G15 elements

A

N: In the atmosphere as N2; NaNO3 (called Chile saltpetre) and KNO3 (Indian saltpetre)
P: In minerals of apatite family Ca9(PO4)6. CaX2 which are the main constituent of phosphate rocks.Phosphoproteins are present
in milk and eggs
As, Sb, Bi: found mainly as sulphide minerals.

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2
Q

Atomic radii of G15

A

N<P<As<Sb<Bi

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3
Q

Ionisation enthalpy of G15

A

N>P>As>Sb>Bi

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4
Q

Electronegativity of G15

A

N>P>As=Sb=Bi

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5
Q

Melting point of G15

A

As>Sb>Bi>P>N

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6
Q

Boiling Point of G15

A

Sb>Bi>As>P>N

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7
Q

Density of G15

A

N<P<As<Sb<Bi

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8
Q

Oxidation states of G15

A

Common O.S. include -3,+3 and +5
The only compound where Bi exists in +5 is BiF5
All oxidation states of N from +1 to +4 disproportionate in acidic medium.
For P all intermediate O.S. disproprtionate ** \to +5 and -3** in bot acidic and alkali medium.

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9
Q

N-N bond vs P-P bond

A

N–N bond is weaker than the single P–P bond because of high
interelectronic repulsion of the non-bonding electrons, owing to the
small bond length.

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10
Q

Reactivity with H of G15

A

Form EH3 hydrides

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11
Q

Reducing character of G15 hydrides

A

BiH3>SbH3>AsH3>PH3>NH3

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12
Q

Basic character of G15 hydrides

A

NH3>PH3>AsH3>SbH3>BiH3

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13
Q

Melting point of G15 hydrides

A

NH3>BiH3>SbH3>AsH3>PH3

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14
Q

Boiling point of G15 hydrides

A

BiH3>SbH3>NH3>AsH3>PH3

The tendency of NH3 to form H-bonds in liquid state reduces due to flipping of structure

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15
Q

Reactivity with O2 of G15

A

form two types of oxides: E2O3 and E2O5.

Nature of E2O3 oxides:
N,P: acidic
As,Sb: Amphoteric
Bi: Basic

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16
Q

Reactivity with Halogens of G15

A

form two series of halides: EX3 and EX5.

Pentahalides are more covalent than trihalides.
All trihalides are stable except for H. For N only NF3 is stable.
BiF3 is ionic in nature while other trihalides are covalent.

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17
Q

Preparation of N2

A

Fractional distillation of liquified air. Boiling point of N2 is less than O2 and so it distills out first.

By reaction of NH4Cl and NaNO3
NH4CI+ NaNO2—->N2 + 2H2O+ NaCl

Thermal decomposition of ammonium dichromate.
(NH4)2Cr2O7—-> N2 + 4H2O + Cr2O3

Very pure nitrogen can be obtained by the thermal decomposition
of sodium or barium azide.
Ba(N3)2—>Ba + 3N2

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18
Q

Properties of N2

A

Dinitrogen is rather inert at room temperature because of the high
bond enthalpy of N-N bond (triple bond). Reactivity, however, increases rapidly with rise in temperature.

Dinitrogen combines with dioxygen only at very high temperature to form nitric oxide, NO. Known as Birkland Eyed Process. A combination reaction which is endothermic

N2 + O2 —> 2NO

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19
Q

Uses of N2

A

1.manufacture of NH3, calcium cyanamide (CaCN2)
2.use where an inert atmosphere is required
3.used as a refrigerant to preserve biological materials, food items and in cryosurgery

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20
Q

Preparation of NH3

A

Hydrolysis of urea
NH2CONH2 + H2O—>(NH4)2CO3—>NH3+H2O+CO2

Ammonium salts with strong acids decompose when treated with base
NH4Cl + Ca(OH)2 —>NH3 + H2O + CaCl2

Haber’s process.
N2+ H2—>NH3

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21
Q

Haber’s Process

A
  1. Low temperature and high pressure (according to Le Chatlier’s principle)
  2. catalyst such as Fe2O3 with small amounts of K2O and Al2O3
  3. Earlier, iron was used as a catalyst with molybdenum as a promoter.
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22
Q

Uses of NH3

A
  1. Ammonia is used to produce various nitrogenous fertilisers
  2. manufacture of some inorganic nitrogen compounds including HNO3
  3. Liquid ammonia is also used as a refrigerant.
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23
Q

Preparation of HNO3

A

Laboratory preparation:
Nitrate salt+H2SO4

Oswald’s process
* Catalytic oxidation of NH3 (Catalyst is Pt-Rh)
NH3 +O2 —> NO +H2O
* NO formed is further oxidised to NO2
NO+ O2—>NO2
* NO2 undergoes disproportionation in acidic medium to give HNO3 and NO
NO2 +H2O —> HNO3 +NO
* NO thus formed is recycled. HNO3 can be concentrated by distillation upto ~ 68%. Further concentration to 98% can be achieved by dehydration with concentrated H2SO4.

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24
Q

Properties of HNO3

A

Reaction with Cu, Ag:
With dil HNO3:
Cu +HNO3 —> Cu(NO3)2 + NO + H2O
With Conc HNO3
Cu + HNO3—> Cu(NO3)2 + NO2 + H2O

Reaction with Zn,Fe:
With dil HNO3:
Zn +HNO3—>Zn (NO3)2 + H2O + N2O
With Conc HNO3
Zn + HNO3—>Zn (NO3)2 + H2O + NO

Some metals (e.g., Cr, Al) do not dissolve in concentrated nitric acid because of the formation of a passive film of oxide on the surface.

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25
Oxidising action of HNO3
I2--->IO3- C---> CO2+H2O S8--->H2SO4 P4--->H3PO4
26
Uses of HNO3
1. pickling of stainless steel 2. etching of metals 3. oxidiser in rocket fuels. 4. manufacture of ammonium nitrate 5. preparation of nitroglycerin, trinitrotoluene and other organic nitro compounds
27
White Phosphorous
**It is poisonous**, insoluble in water but soluble in carbon disulphide and **glows in dark** (chemiluminescence). It is more reactive than the other solid phases because of angular strain in the P4 molecule where the angles are only 60°. It consists of **discrete tetrahedral P4 molecule.** P4+ NaOH +H2O--->PH3+NaH2PO2 P4 + O2--->P4O10
28
Red phosphorous
Red phosphorus is obtained by **heating white phosphorus** at 573Kin **an inert atmosphere for several days**. It is odourless, **nonpoisonous** and insoluble in water as well as in carbon disulphide.It is much **less reactive** than white phosphorus. It **does not glow in the dark**. It is **polymeric**, consisting of chains of P4 tetrahedral linked together.
29
Black phosphorous
Black phosphorus has two forms a-black phosphorus and b-black phosphorus. a-Black phosphorus is formed when **red phosphorus is heated** in a sealed tube at **803K**. It can be sublimed in air and has opaque **monoclinic or rhombohedral crystals**. It does not oxidise in air. b-Black phosphorus is prepared by **heating white phosphorus at 473 K** under high pressure. It does not burn in air upto 673 K.
30
Preparation of PH3
Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl. Ca3P2 + H2O --->Ca(OH)2 + PH3 When pure, it is **non inflammable** but **becomes inflammable** owing to the **presence of P2H4 or P4 vapours**. To **purify it** from the impurities, **it is absorbed in HI** to form phosphonium iodide **(PH4I**) which on **treating with KOH** gives off **phosphine.** PH4I + KOH ---> KI + H2O + PH3
31
Properties of PH3
1. It is a colourless gas with **rotten fish smell** and is highly **poisonous.** 2. It **explodes** in contact with traces of **oxidising agents** like HNO3, Cl2 and Br2 vapours 3. The solution of PH3 **in water decomposes** in presence of light giving **red phosphorus and H2.**
32
Uses of PH3
1. Holme’s signals. 2. It is also used in smoke screens.
33
PCl3
**Preparation** It is obtained by **passing dry chlorine over heated white phosphorus.** P4 + Cl2--->PCl3 It is also obtained by the **action of thionyl chloride with white phosphorus.** P4 + SOCl2--->PCl + SO2 + **S2Cl2** **Properties** It is a colourless oily liquid and hydrolyses in the presence of moisture. PCl3 + H2O--->H3PO3+HCl
34
PCl5
**Preparation** Phosphorus pentachloride is prepared by the **reaction of white phosphorus with excess of dry chlorine.** P4 +Cl2--->PCl5 It can also be prepared by the action of **SO2Cl2** on phosphorus. P4 +SO2Cl2 --->PCl5 +SO2 **Properties** **PCl5 is a yellowish white powder** and in moist air, it **hydrolyses to** POCl3 and finally gets converted to **phosphoric acid.** PCl5 + H2O --->POCl3 + HCl POCl3 + H2O---> H3PO4 + HCl When heated, it sublimes but **decomposes on stronger heating.** PCl5--->PCl3 + Cl2
35
Oxoacids of P
The acids which contain P–H bond have strong reducing properties. Thus, hypophosphorous acid is a good reducing agent as it contains two P–H bonds.
36
Occurence of G16
Also known as chalcogens Sulphur: gypsum **CaSO4.2H2O** epsom salt **MgSO4.7H2O**, **baryte BaSO4** galena PbS, zinc blende ZnS, copper pyrites CuFeS2, **H2S in volcanoes**, eggs, proteins, garlic, onion, mustard, hair and wool contain sulphur. Selenium and tellurium are also found as metal selenides and tellurides in sulphide ores.
37
Atomic Radii of G16
Increases down the group
38
Ionisation Enthalpy of G16
Decreases down the group
39
Electron Gain Enthalpy of G16
S>Se>Te>O
40
Electronegativity of G16
Decreases down the group
41
Melting and Boiling points of G16
Increases down the group
42
Physical properties of G16
* Oxygen and sulphur are non-metals, selenium and tellurium metalloids * All these elements exhibit allotropy. * The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of their atomicity (O exists as O2 and S exists as S8)
43
Oxidation States of G16
Sulphur, selenium and tellurium usually show + 4 oxidation state in their compounds with oxygen and + 6 with fluorine.
44
Reactivity of G16 with H2
* Acidic character: H2O< H2SH2S>H2Se>H2Te * Boiling point/ Melting point: H2O>H2Te>H2Se>H2S
45
Reactivity of G16 Oxygen
* Ozone (O3) and sulphur dioxide (SO2) are gases while selenium dioxide (SeO2) is solid. * Reducing property of dioxide decreases from SO2 to TeO2(TeO2 is oxidising) * All oxides are acidic in nature
46
Reactivity of G16 with halogens
* hexafluorides are the only stable halides. Sulphur hexafluoride, SF6 is exceptionally stable for steric reasons. * Amongst tetrafluorides, SF4 is a gas, SeF4 a liquid and TeF4 a solid. * All elements except oxygen form dichlorides and dibromides. * S2F2, S2Cl2, S2Br2, Se2Cl2 and Se2Br2. These dimeric halides undergo disproportionation SeCl2 ---> SeCl4 +Se
47
Preparation of dioxygen
1. KClO3 ---> KCl +O2 (catalyst is MnO2) 2. Thermal decomposition of low reactive metals like Ag, Pb, Hg, etc. 3. H2O2---> H2O +O2 4. Electrolysis of H2O 5. Liquefication of air followed by fractional distillation.
48
Uses of dioxygen
1. oxygen is used in oxyacetylene welding 2. manufacture of many metals, particularly steel 3. combustion of fuels like hydrazines in liquid oxygen as thrust in rockets.
49
Preparation of Ozone
When a slow **dry stream of oxygen** is **passed through a silent electricaldischarge**, conversion of oxygen to ozone (10%) occurs. The product is known as **ozonised oxygen**. 3O2 ---> 2O3 Since the formation of ozone from oxygen is an **endothermic process**, it is necessary to use a **silent electrical discharge** in its preparation to **prevent its decomposition**.
50
Properties of O3
Ozone is thermodynamically unstable with respect to oxygen since its decomposition into oxygen results in the liberation of heat . **High concentrations of ozone can be dangerously explosive.** It acts as a **powerful oxidising agent**. Converts PbS---> PbSO4 and I- --->I2 Due to the ease with which it liberates atoms of nascent oxygen (O3 ---> O2 + O) and thus is a bleaching agent.
51
Estimation of O3
ozone reacts with an **excess of potassium iodide** solution buffered with a **borate buffer** (pH 9.2), **iodine is liberated** which can be **titrated against** a standard solution of **sodium thiosulphate**. This is a quantitative method for estimating O3 gas.
52
Uses of O3
* It is used as a germicide, disinfectant and for sterilising water * bleaching * manufacture of potassium permanganate.
53
Allotropic forms of S
Alpha-S or rhombic form: This allotrope is **yellow in colour.** Rhombic sulphur crystals are formed on **evaporating the solution of roll sulphur in CS2**. It is insoluble in water but dissolves to some extent in organic solvents. It is readily soluble in CS2. Beta-S or monoclinic form: This form of sulphur is prepared by **melting rhombic sulphur in a dish and cooling, till crust is formed**. On removing the crust, colourless needle shaped crystals of b-sulphur are formed. At **369K the two forms exist in equilibrium**. Below 369K alpha is more stabe and above 369K beta is more stable. At elevated temperatures **(~1000 K), S2 is the dominant** S2 species and is paramagnetic like O2.
54
Preparation of SO2
* sulphur is burnt in air or oxygen S +O2 ---> SO2 * treating a sulphite with dilute sulphuric acid (SO3)2- + H+ ---> SO2 +H2O * roasting of sulphide ores.
55
Properties of SO2
Sulphur dioxide is a colourless gas with pungent smell and is highly soluble in water. It liquefies at room temperature. Sulphur dioxide, when passed through water, forms a solution of **sulphurous acid.** SO2 +H2O ----> H2SO3 Sulphur dioxide reacts with chlorine in the presence of **charcoal** to give **sulphuryl chloride, SO2Cl2**. SO2 + Cl2 ---> SO2Cl2 When **moist, sulphur dioxide behaves as a reducing agent**. It converts **iron(III) ions to iron(II)** ions and decolourises acidified potassium permanganate(VII) solution
56
Uses of SO2
(i) in refining petroleum and sugar (ii) in bleaching wool and silk (bleaching action of SO2 is temporary) (iii) as an anti-chlor, disinfectant and preservative
57
Contact Process
* burning of sulphur or sulphide ores in air to **generate SO2**. * **conversion of SO2 to SO3** by the reaction with oxygen in the presence **catalyst (V2O5)**. SO2 + O2 ---> SO3 Reaction is **exothermic, reversible** and the forward reaction leads to a decrease in volume. **Low temperature and high pressure** are the favourable conditions for maximum yield. **2 bar and a temperature of 720 K.** * **absorption of SO3 in H2SO4** to give Oleum (H2S2O7). SO3 +H2SO4 --->H2S2O7 The sulphuric acid obtained by Contact process is **96-98% pure**
58
Properties of H2SO4
It dissolves in water with the evolution of a large quantity of heat. The concentrated **acid must be added slowly into water with constant stirring**. Chemical properties include (a) low volatility (b) strong acidic character (c) strong affinity for water (d) ability to act as an oxidising agent. It has evident by its charring action on carbohydrates. **Oxidising property of mineral acids HNO3>H2SO4> H3PO4**
59
Uses of H2SO4
1.manufacture of fertilisers 2.petroleum refining 3.manufacture of pigments, paints and dyestuff intermediates 4. detergent industry 5. metallurgical applications (e.g., cleansing metals before enameling, electroplating and galvanising) 6. storage batteries 7. in the manufacture of nitrocellulose products 8. as a laboratory reagent.
60
Colors of O3
Pure ozone is a pale blue gas, dark blue liquid and violet-black solid.

Inorganic Chemistry (14 decks)

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