EAMCET QR Chemistry Sr Chem 10.VA Group Elements 171-175

8/8/2019 EAMCET QR Chemistry Sr Chem 10.VA Group Elements 171-175

1/12

1

10 . GROUP 15 ELEMENTS (V A GROUP ELEMENT S)

Synopsis :

VA group elements are Nitrogen (N) (7), Phosphorus (P) (15), Arsenic (As) (33), Antimony (Sb)

(51), Bismuth (Bi) (83). These elements are called as pnicogens. Their compounds are called pnictides. 78% of Atmosphere posses Nitrogen. It is also available in the form of nitrate salts in earths crust.

Eg : Salt petre KNO3, Chile salt petre NaNO3 etc,.

Most abundant element of this group in earths crust is P. The important minerals of phosphorus are phosphate rocks, fluorapatite [3Ca3(PO4)2, CaF2],

phosphorite [Ca3(PO4)2] etc,.

These are pBlock elements with ns2 np3 configuration.

As the P orbitals in the outermost shells are half-filled these elements are stable. Nitrogen is a gas, P, As, Sb and Bi are solids. Nitrogen and Phosphorus are non metals, Arsenic and antimony are metalloids and Bismuth is a

metal.

Nitrogen exists as triple bonded diatomic gaseous molecule. Bismuth is a metal (monoatomic). P, As and Sb exists as tetratomic, tetrahedral molecules. The existence of Nitrogen as diatomic molecule is due to existence of p - P multiple bonds. The bond dissociation energy of Nitrogen is 945.4kJ. (225 kcal/mole) p - P multiple bonds are not possible in other elements due to repulsion between non bonded

electrons of the inner core.

Phosphorus form layered structures with a co-ordination number of3.

P4 has a regular tetrahedral structure having one P atom at eachvertex of the tetrahedron. The bond angle PPP is 60.

Atomic size increases from Nitrogen to Bismuth, less increase fromAs to Bi is because of less shielding effect of (n-1) d electrons.

Due to smaller size of nitrogen its electronegative value is high. Electronegativity decreases from nitrogen to Bismuth. B.P. increases from Nitrogen to Bismuth. M.P. increases from Nitrogen to Arsenic and then decreases.

Low M.P of nitrogen is due to its diatomic discrete gaseous molecules. Due to large size and metallic character the M.P. of antimony and Bismuth decreases. Nitrogen in solid state exists in cubic crystalline structure ( - nitrogen) and hexagonal crystalline

structure ( - nitrogen). Phosphorous exists in white, red, scarlet, violet, - black, - black etc. forms. Nitrogen can form a chain of two atoms (NH2NH2) and a chain of three atom (N3

(-)).

Less catenation capacity for Nitrogen is due to less dissociation energy of N N bond. Phosphorus forms (P2H4). The general oxidation states of these elements are +3 and +5 and 3 (except Bi). Stability of + 3 form increases from nitrogen to bismuth and + 5 decreases due to inert pair effect.

PP

P

P

60


2/12

V A Group Elements

2

Nitrogen show various oxidation states because of small size and high electronegativity. It shows 3 in Li3 N, Mg3 N2, Ca3 N2 etc.

2 in N2H

4 1 in NH2OH

3

1in N3H

0 in N2

+ 1 in N2O

+ 2 in NO

+ 3 in N2O3

+ 4 in NO2+ 5 in N2O5

Phosphorous show 3 in Zn3 P2, Ca3 P2.

Nitrogen can show maximum covalency of 4 (NH4+). Remaining elements shows covalency of 5 and a maximum of 6 as in AsF6

(), PCl6().

Phosphorous is reactive due to the presence of single P P covalent bonds.HYDRIDES :

These elements form hydrides of the type MH3NH3(Ammonia) PH3(Phosphine)

AsH3(Arsine) SbH3(Stibine)

BiH3 (Bismuthine)

NH3 to BiH3 the stability decreases. The size of the central atom increase and there by the metal hydrogen bond becomes weaker due

to decreased overlap between the large central atom and the small H atom. Reducing character of these hydrides gradually increases. Stibine and bismuthine are strong

reducing agents.

All the hydrides can be prepared in similar methods. On hydrolysis of binary compounds of these metalswith water or dilute acids gives these hydrides.

Mg3N2 + 6H2O 3Mg (OH)2 + 2NH3Ca3P2+ 6HCl 3CaCl2 + 2PH3

NH3 and PH3 are volatile , colourless gases. The thermal stability of this hydrides decreases from NH3to BiH3 due to decrease in M H bond

energy.

These hydrides have a pyramidal shape with a lone pair of electron on the central atom. In NH3 N is sp

3 hybridised in other hydrides central atom uses pure p-orbitals.

In NH3 the bond angle is 107. In PH3 the bond angle is 94. Due to presence of lone pair of electrons on the central atom these hydrides acts as lewis bases. The basic nature decreases as follows

NH3> PH3> AsH3> SbH3> BiH3

Due to decrease in the electron density of the lone pair on the central atom.

When Hydrogens are methylated basic nature increases PH3 < P(CH3)3.

Because of donation of lone pair of electron by NH3 to H+

ion NH4+

ion forms.

Phosphonium (PH4+) ion is less stable.


3/12

V A Group Elements

3

Due to high electronegative difference between Nitrogen and Hydrogen NH3 is capable of forminghydrogen bonding.

HH|NH...........

H

H

|

|NH.......

H

H

|

|NH.......

H

H

|

|NH

MH bond energies NH3>PH3> AsH3 > SbH3> BiH3From NH3 to BH3 :

1) Thermal stability decreases

2) Reducing character increases

3) Basic nature decreases4) Complex forming ability decreases

5) Ease of formation of hydrides decreases

HALIDES :

All trihalides of these elements are possible except NBr3 and NI3 due to large size difference. Trihalides are covalent and have a tetrahedral structure. Trichlorides act as Lewis acids by utilizing the vacant d- orbitals. On hydrolysis of NCl3 the products are NH3 and HOCl. On hydrolysis of PCl3 the main product is H3PO3 (Phosphorous acid). On hydrolysis of ASCl3 the main product is H3ASO3 (Arsenious acid). On hydrolysis of SbCl3 the main product is SbOCl (Antimony chloride). On hydrolysis of BiCl3 the main product is BiOCl (Bismuthyl chloride).

In SbOCl and BiOCl the radicals are SbO+ and BiO+ are present.

With the increasing metallic character of the elements the halides become more ionic and theirtendency towards hydrolysis decreases.

PF3 and PF5are not hydrolysed because PF bonds are stronger bonds than P O bonds.

With the increase in the metallic character of the elements the halides become more ionic and theirtendency towards hydrolysis decreases.

All these elements except N and Bi doesnt form pentahalides. N because of non available vacantd orbitals and Bi due to inert pair effect.

PCI5 and SbCl5 exists in triagonal bipyramid structures. But as some bond angles are 90 and some are of 120 they are not stable.

PCl5 PCl3 + Cl2(chlorinating agent) Hydrolysis of PCl5 gives orthophosphoric acid.

PCl5 + 4H2O H3PO4+ 5HCl Solid PCl5 is ionic compound consisting of [PCl4]

+, [PCl6()] cation is tetrahedral anion is

octahedral.

PBr5 exists as [PBr2] Br3().

OXIDES :

Oxides of Nitrogen :

Oxides of N2 are endothermic (except N2O5) and acts as better oxidants. Except N2O5 all are gases. N2O (Laughing gas): First prepared by priestly. Berthelot prepared it from Ammonium nitrate or ammonium sulphate and sodium nitrate.

OH2ONNONH 22C250

34

0

+


4/12

V A Group Elements

4

( ) 42223424 SONaOHONNaNO2SONH +++

It is colourless neutral gas. Fairly soluble in cold water.

It is incombustible but supports combustion of Mg and P.Mg + N2O MgO + N2P4 + 10 N2O P4O10 + 10N2

Oxidising property : - It oxidises metals.Cu(hot)+ N2O CuO + N2

Mixture of O2 and N2O is used as anaestheic in surgery and dentistry. In the presence of acidified potassium permanganate it undergoes oxidation to give nitric oxide.

NO10OH3MnSO2SOKON5SOH3KMnO2 24422424 +++++

Structure : N2O is hybrid of following structures. It is a linear molecule.

( ) ( ) ( )

+=+= ONNONN

Nitric oxide (NO) Nitrogen monoxide : (Priestley)

1) ( ) OH4NO2NOCu3HNO8Cu3 2233 +++

2) Catalytic oxidation of Ammonia gives Nitric oxide. ( Ostwards method) .

OH6NO4O5NH4 2m600C900

gauzept23

0+ +

3) By passing electric arc through N2 and O2

N2 + O2 2NOProperties :

NO is colourless gas and heavier than air.

At 12 K it freezes to Blue solid & its M.P is 1232 K. On reaction with oxygen it gives reddish brown fumes.

2NO + O2 2NO2 NO is most thermally stable oxide of N2.

22C900

ONNO20

+

Oxidising properties :H2S + 2NO H2O + N2O + S2Cu + 2NO 2CuO + N2

In the manufacture of H2SO4 by lead chamber process NO is used as catalyst.Structure : NO has 11 valence electrons

(N 5, O 6). Presence of odd, electron makes it as paramagnetic. It doesnt dimerises due to delocalised odd electron.

+

==

+ONONON

)(

In liquid and solid states it dimerises hence it is diamagnetic.Nitrogen sesquioxide or dinitrogen trioxide (N2O3) :

N2O3 is a hydride of nitrous acid.N2O3 + H2O 2HNO2


5/12

V A Group Elements

5

By cooling a mixture of NO and NO2 in equimolar ratio to 20C N2O3 is obtained.NO + NO2 N2O3

On action of Cu on HNO3 N2O3 is obtained.

2Cu + 6HNO3 N2O3 + 2Cu (NO3)2 + 3H2O It is blue liquid and a pale blue solid. M.P is 102 C. It is acidic oxide. Its salts are called as nitrites.

2NO + 2KOH KNO2 + H2OStructure :

i) ii)

Nitrogen Dioxide : It is reddish brown gas. It dimerises to dinitrogen tetraoxide which is colourless solid.

cdiamagnetisolidColourless42

C11

icParamagnetBrown2 ONNO2

0

Reduction of conc nitric acid with metals like Cu, Ag gives NO2.Cu + 4HNO3 2CuO + 4NO2 + O2

Lead nitrate on heating gives NO2( ) 2223 ONO4PbO2NOPb ++

NO2 dissolves in water to give nitrous and nitric acids hence it is called as mixed anhydride of

HNO2 and HNO3.2NO2 + H2O HNO2+ HNO3

Structure : NO2 has angular structure with a bond angle of 132 . It posses a three electron bond

and hence it is coloured and paramagnetic.

The structure of N2O4 :

O

N

O

N

O O

N

O

O

N

O

O

N

O

O

O

O

N

O

N

O

O

N

O

N NO

O

O N N O

O

O


6/12

V A Group Elements

6

It turns ferrous sulphate solution black. NO2 gives nascent oxygen hence it acts as oxidizing agent NO2 NO + (O)

SO2 + NO2 + H2O H2SO4 + NO

H2S + NO2 S + NO + H2O When reacts with alkalis it form nitrates and nitrites.2NO2 + 2KOH KNO2 + KNO3 + H2O

Nitrogen pentaoxide :

On dehydration of Nitric acid with the help of phosphorous pentoxide N2O5 is obtained.

OHONHNO2 252OP

3104 +

4AgNO3 + 2Cl24AgCl + 2N2O5 + O2 N2O5 is white solid. M.P. 35C. Above its melting point it decomposes to N2O4 and O2 .

2N2O5 + H2O 2HNO3 It is anhydride of nitric acid.

N2O5 + H2O 2HNO3 It reacts with bases to give nitrate salts.

N2O5 + 2NaOH 2NaNO3 + H2O As it decomposes easily it acts as powerful oxidizing agent.

Structure :

It is an ionic solid i.e, Nitronium nitrate (NO2+,NO3

)

O

O

O

O

NON

O

O

O

O

NON

As the size of the central atom increases the basic property increases. Phosphorous forms the following oxides.

+3 +4 +5

P2O3 P2O4 P2O5

P2O3 and P2O5 exist as dimmers P4O6 and P4O10.P4O6 P4O10

Phosphorus is linked Phosphorus is linked to

to 3 oxygens 4 oxygens

P

P

P

P

P

P

P

P


7/12


8/12

V A Group Elements

8

A mixture of 1 : 1 conc HNO3 and Conc H2SO4 is known as nitration mixture

It is used in nitration reaction of organic compounds like Benzene, Toluene and phenol

C6H6 + HNO32 4H SOC6H5NO2 + H2O

It is a very strong oxidising agent. It oxides non-metals to their corresponding oxides or oxoacidsP4 + 20HNO3 4H3PO4 + 20NO2 + 4H2O

C + 4HNO3 CO2 + 4NO2 + 2H2O

The structure of nitric acid is

H O N O

O

=| |

HO N O

O

This is a monobasic acid

It is a strong oxidising agent

Pernitric acid : HNO4 is called as per nitric acid.

O

O||NOHO

Oxyacids of phosphorous :

Hypophosphorous acid : (H3 PO2) Salts are called as hypophosphates.

It decomposes on heating to give PH3. The acid and its salts are powerful reducing agents. Basicity of H3PO2 is one.

Structure :

H

O

H

||

|POH (or)

Ortho Phosphorous acid : (H3PO3) Forms two series of salts phosphite (Normal) and hydrogen phosphite (Acidic).

Decomposes on heating to give PH3 and H3PO4. It gives two series of salts primary phosphites (H2PO3) and secondary phosphites (HPO3

2).

H3PO4 and its salts are good reducing agents. Structure :

OH

H

O

|

||PHO (or)

Orthophosphoric acid (H3PO4) :

H

P

O

HOH

O

P

H

HOO


9/12

V A Group Elements

9

Ca3(PO4) with H2SO4 gives H3PO4. P2O5 on hydrolysis gives H3PO4. Forms three types of salts (basicity is three).

Dihydrogen phosphate )42POH .Hydrogen phosphate )24HPO .Phosphate )34PO .

It is syrupy liquid due to hydrogen bonding. The acid looses water steadily on heating.

H3PO4 heatinggently

H4P2O7 heatingstrong

HPO3(orthophosphoric acid) (pyrophosphoric acid) (meta phosphoric acid)

Structure :

H

HO

HO

O

PO

=

Used in the preparation of HBr and HI.Pyrophosphoric acid : (H4P2O7) :

It forms salts of type M4P2O7 and M2H2P2O7. Ca2P2O7 is used in fluoride tooth pastes.

Na2H2P2O7 is used in making bread. It is a Tetrabasic acid.Structure :

O

OH

OH

|

|PO

OH

OH

|

|PO ==

Metaphosphoric acid (HPO3) :

By heating H3PO4 or H4P2O7 it is obtained.

As it is transparent, glassy solid it is known as glacial phosphoric acid. Its salts are known as metaphosphates . Free monophosphate (PO3

) ions doesnt exist where as it forms a ring compounds like

triphosphates, tetraphosphates or polyphosphates.

Its polymeric sodium metaphosphates are called as Grahams salt , Kurrols salt and madrells salt(NaPO3)n.

It is a monobasic acid.Structure :

O

O||PHO =

O

P

O

OO

H

H

O

P

O

O

H

H

O


10/12

V A Group Elements

10

Hypophosphoric acid (H4P2O6) :

It is a tetrabasic acid.

Structure :

OH

OH

O

|

||P

OH

O

|

||PHO

Peroxy phosphoric acid( H3PO5) :

It is a Tribasic acid.

Structure :

OHO

OH

O

|

||PHO

PREPARATION AND USES OF NITRIC ACID : (HNO3)

3HNO is the most important oxy acid of Nitrogen

HNO3 is prepared on large scale by

1) Birkland-Eydes process (Arc process)

2) Ostwalds process (from ammonia)

BIRK LAND-EYDES PROCESS used at places where electric power is cheap.PRINCIPLE:-

2 2 2 ; 180.7Electric arc

N O NO H kJ + = +

2 22 2NO O NO+

2 2 2 3

4 2 4NO O H O HNO+ +

OSTWALDS PROCESS (FROM AMMONIA) :NH3 mixed with air in 1 : 7 or 1 : 8 when passed over a hot platinum gauze catalyst is oxidised

(95%) to NO

4NH3 + 5O2 1155pt gauze

K 4NO+6H2O+1275 K.J

The liberated heat keeps the catalyst hotThe NO gas is cooled and mixed with oxygen to get NO2 in oxidation chamber.

Then it is passed into warm water under pressure in presence of excess air where HNO3 is

formed.

4NO2+O2+2H2O 4HNO3The acid formed is about 61% concentrated.

Concentration of HNO3 :

The crude HNO3 is concentrated in three stages

Stage-1 61% HNO3 is distilled until 68% HNO3 is obtained

Stage-2 68% HNO3 is mixed with Conc H2SO4 and distilled again where 98% acid is obtained.

Stage-3 98% HNO3 is cooled in a freezing mixture then crystals of pure HNO3 seperates out.

Uses of HNO3 :

In the manufacture of fertilisers like basic calcium nitrate [CaO.Ca(NO3)2]

In the preparation of explosives like TNT, nitroglycerine etc.

POO

HO

P

HO O

OOH

H


11/12

V A Group Elements

11

as nitration mixture along with H2SO4

In the preparation of perfumes, dyes and medicines HNO3 is a very strong oxidising agent used in the oxidation of cyclohexanol or Cyclohexanone

to adipic acid, p-xylene to terepthalic acid In the preparation of artificial silk i.e cellulose nitrate

Ammonia : Distillation of NH4

+salt with a base gives ammonia.

NH4Cl + NaOH NaCl + NH3+ H2OCyanamide process :

Calcium carbide on reaction with nitrogen gas at 1273k in the presence of CaCl2 or CaF2 ascatalyst gives calcium cyanamide and graphite mixture. This is called as nitrolim.

CCaCNNCaC 2

K13781273

22 + +

Hydrolysis of cyanamide with steam gives NH3.

33K453

22 NH2CaCOOH3CaCN + +

Haber Bosch process :

H2 and N2 gives in 3 : 1 ratio with iron as catalyst and Mo or small amounts of mixture ofpotassium and aluminium oxides (K2O and Al2O3) as promoter and at a pressure of 200 atm, 725

775 k. gives ammonia.

N2+ 3H2 2NH3 ; H = - 93.63 kJ In serpecks process by product is NH3. Quick lime is used to dry NH3.

CaCl2, P2O5 and H2SO4 are acidic hence they cant be used as drying agents for NH 3. At 20C 1 litre H2O dissolves 700 litres of NH3. Saturated sol of NH3 at room temperature contains 35% (w/w) NH3. NH3 in the presence of catalyst gives NO. NH3 with hot CuO gives N2 gas. With lesser Cl2 on oxidation NH3 gives N2 and with excess Cl2 gives NCl3. NH3 is Lewis base. NH3 acts as ligand and forms complexes like

[Ag (NH3)2]+, [Cu(NH3)4]

2+etc.

Uses of Ammonia : NH3 is used in refrigeration due to high latent heat of evaporation. For nitrogenous fertilizers like ammonium sulphate, urea, calcium ammonium nitrate etc.

Preparation, ammonia is the starting material.

In the manufacture of sodium carbonate by Solvay process ammonia is used. In the preparation of rayon and artificial silks, explosive like ammonium nitrate, ammonia is

required.

Nitric acid manufacture (by Ostwarlds process), explosive like ammonium nitrate, ammonia isrequired.

Liquior ammonia is useful as a good solvent for both ionic as well as covalent compounds.

Structure : Pyramidal in shape, Hybridisation sp3

.


12/12

V A Group Elements

12

A mixture of CaC2 + Ca3 P2 is used as Holmes signals. Superphosphate of lime (calcium superphosphate) Ca(H2PO4)2 + 2(CaSO4 .2H2O) Mixture of calcium dihydrogen phosphoate [Ca(H2PO4)2] and gypsum (CaSO4.2H2O) is known as

super phosphate of lime.

Powdered phosphate rock (calcium phosphate) on treating with concentrated sulphuric acid

(chamber acid)Ca3(PO4)2+2H2SO4+4H2O

Ca(H2PO4)2+ 2(CaSO4. 2H2O) + heat

The reaction between phosphate rock and conc. H2SO4 is allowed to take place for 24 36 hours. In the above reaction the temperature rises to about 373 383 K. The carbonate and the fluoride impurities in the phosphate rock react with H2SO4 and liberate CO2

and HF gases.

Uses: Superphosphate of lime is a good phosphate fertilizer. CaSO4 present in superphosphate of lime is insoluble waste product. To avoid it superphosphate is

changed into triple phosphate which is completely dissolves in water.

N

H H H

H

H

H

EAMCET QR Chemistry Sr Chem 10.VA Group Elements 171-175

Documents

Transcript of EAMCET QR Chemistry Sr Chem 10.VA Group Elements 171-175