group 15 - nitrogen

8/6/2019 Group 15 - Nitrogen

http://slidepdf.com/reader/full/group-15-nitrogen 1/39

Group 15 : Nitrogen &Group 15 : Nitrogen &

Its CompoundsIts Compounds4.1 Nitrogen : Its Inert4.1 Nitrogen : Its Inert

Nature & its ExtractionNature & its Extractionfrom Airfrom Air



The Inert Nature of NitrogenThe Inert Nature of Nitrogen

N atom :1sN atom :1s22 2s2s22 2p2p33 -- achievesachievesstable octet electron arrangementstable octet electron arrangement

through formation of covalent bondsthrough formation of covalent bondsin the nitrogen molecule.in the nitrogen molecule.

Consists of simple diatomicConsists of simple diatomicmoleculesmolecules ±± covalent triple bond.covalent triple bond.



N molecule is very stable & relatively inert.N molecule is very stable & relatively inert. ReasonsReasons ::a) The two N atomsa) The two N atoms ±± held by a very strong triple bondheld by a very strong triple bond

±±very short bond length & very high bond energy.very short bond length & very high bond energy.

NN22 (g) 2N(g) H = + 945 kJmol(g) 2N(g) H = + 945 kJmol--11

Since a large amount of energy is needed toSince a large amount of energy is needed to

dissociate thedissociate themolecule, nitrogen is relatively chemically inert.molecule, nitrogen is relatively chemically inert.b) Nitrogen molecule is linear & nonb) Nitrogen molecule is linear & non--polar. N moleculepolar. N molecule

hashas symmetrical distribution of electrons. Nsymmetrical distribution of electrons. Nmolecule is notmolecule is not reactive due to absence of polarity.reactive due to absence of polarity.

* At high temperature & pressure, nitrogen can react with hydrogen to form ammonia,* At high temperature & pressure, nitrogen can react with hydrogen to form ammonia,oxygen to form nitric oxides & metals to form metal nitrides.oxygen to form nitric oxides & metals to form metal nitrides.



Extraction of Nitrogen from Air Extraction of Nitrogen from Air AirAir ±± main source of nitrogen. Reason : airmain source of nitrogen. Reason : air

consists of up to 78% nitrogen by volume.consists of up to 78% nitrogen by volume. Nitrogen is extracted from air by fractionalNitrogen is extracted from air by fractional

distillation of liquid air.distillation of liquid air.

Consists of 2 stagesConsists of 2 stages :: *refer ace ahead vol.2 (chap.4) pg. 57/ Longman*refer ace ahead vol.2 (chap.4) pg. 57/ Longmanchap.5 pg. 83chap.5 pg. 83

a)a) Liquefaction of airLiquefaction of air Clean air (after removal of dust particles andClean air (after removal of dust particles and carbon dioxide) is fed into a compressorcarbon dioxide) is fed into a compressor --

compressedcompressedunder high pressure about 250 atm and lowunder high pressure about 250 atm and lowtemperaturetemperature until liquefieduntil liquefied -- Left onlyLeft onlyNitrogen and Oxygen gas inNitrogen and Oxygen gas in

the liquid air.the liquid air.



b)b) Fractional distillationFractional distillation

Nitrogen gas collected beforeNitrogen gas collected beforeoxygenoxygen

because nitrogen has lower boilingbecause nitrogen has lower boiling

pointpointthan oxygen :than oxygen :

-- nitrogen (nitrogen (--196196 °°C)C)

-- oxygen (oxygen (--183183 °°C)C)



QuestionsQuestions::

Nitrogen dioxide and dinitrogen tetroxide exists inNitrogen dioxide and dinitrogen tetroxide exists inequilibrium in the gas phase. Which of the followingequilibrium in the gas phase. Which of the followingstatements is true?statements is true?

A. NA. N22OO44 molecule has two dative bond.molecule has two dative bond.

B. NOB. NO22 molecule has one sigma and one pi bonds.molecule has one sigma and one pi bonds.C. The bond angle in NOC. The bond angle in NO22 molecule is 120molecule is 12000..

D. The hybridisation of nitrogen atom in ND. The hybridisation of nitrogen atom in N22OO44

molecule ismolecule is spsp33..

SolutionSolution:: NN22OO44 has two dative bonds and undergoeshas two dative bonds and undergoes spsp22

hybridisationhybridisation..

NONO22 has two sigma bonds and one pi bondhas two sigma bonds and one pi bondand the bondand the bond angle is less than 120angle is less than 12000 because of because of the repulsion from the oddthe repulsion from the odd

electron.electron.



A catalytic converter reduces air pollution byA catalytic converter reduces air pollution by1 oxidising lead to lead (II) oxide1 oxidising lead to lead (II) oxide

2 reduces oxides of nitrogen to nitrogen and oxygen2 reduces oxides of nitrogen to nitrogen and oxygen

3 oxidising carbon monoxide and hydrocarbons to3 oxidising carbon monoxide and hydrocarbons tocarbon dioxidecarbon dioxide

and water.and water.

Solution : A catalytic converter reduces NO and NOSolution : A catalytic converter reduces NO and NO22 totoNN22 and Oand O22 inin one chamber and oxidises CO andone chamber and oxidises CO andunburnt hydrocarbons tounburnt hydrocarbons to

COCO22 in the other.in the other.

Answer : C (2 & 3)Answer : C (2 & 3)



The photochemical smog is a type of air pollution.The photochemical smog is a type of air pollution.The gas which causes the pollution isThe gas which causes the pollution is

A. OA. O33

B. NOB. NO

C. NOC. NO22

D. SOD. SO22

Solution : NOSolution : NO22 combines with the hydrocarbon fromcombines with the hydrocarbon fromautomobileautomobile exhausts to produceexhausts to producephotochemical smog. First, ultravioletphotochemical smog. First, ultraviolet lightlightcauses the formation of oxygen radicals from NOcauses the formation of oxygen radicals from NO22..

TheThe oxygen radical subsequently reacts withoxygen radical subsequently reacts withOO22 to form Oto form O33. The. The ozone combines withozone combines withunsaturated hydrocarbon to formunsaturated hydrocarbon to form organicorganicradical which then combines with NO to form theradical which then combines with NO to form the

component of smog.component of smog.

Answer : CAnswer : C



Which of the following reactions occur(s) in a catalyticWhich of the following reactions occur(s) in a catalytic

converter?converter?1 2CO(g) + O1 2CO(g) + O22 2CO2CO22(g)(g)

2 2NO(g) + 2CO(g) N2 2NO(g) + 2CO(g) N22(g) + 2CO(g) + 2CO22(g)(g)

3 2C3 2C88HH1818(g) + 25O(g) + 25O22(g) 16CO(g) 16CO22(g) +(g) +18HO18HO22(g)(g)

Solution : In a catalytic converter, CO is oxidised to COSolution : In a catalytic converter, CO is oxidised to CO22

whereas NOwhereas NO is reduced to Nis reduced to N22. Hydrocarbons. Hydrocarbonsare oxidised to COare oxidised to CO22..

Answer : D (1,2 & 3)Answer : D (1,2 & 3)



4.2 AMMONIA: ITS4.2 AMMONIA: ITS

FORMATION,FORMATION,

PROPERTIES ANDPROPERTIES AND

ITSITS



WHAT IS AMMONIA???WHAT IS AMMONIA???



FORMATION OF AMMONIA FROMFORMATION OF AMMONIA FROM

AMMONIUM SALTSAMMONIUM SALTS

Ammonia gas is prepared by heating a mixture of Ammonia gas is prepared by heating a mixture of

ammonium salt and a base (Examples: NaOH, KOH,ammonium salt and a base (Examples: NaOH, KOH,

CaO)CaO)

Ammonium salt + base Ammonia gasAmmonium salt + base Ammonia gas

NH NH44++ + OH NH+ OH NH33 +H2O+H2O

Ammonia gas is dried by passing through anhydrousAmmonia gas is dried by passing through anhydrous

Calcium Oxide and it is collected by upward deliveryCalcium Oxide and it is collected by upward delivery

Concentrated HConcentrated H22SOSO44 and anhydrous CaCland anhydrous CaCl22 areare

common dehydrating agents that cannot be usedcommon dehydrating agents that cannot be used



PROPERTIESPROPERTIES

Ammonia is:Ammonia is:

1.1. -- Colourless, PungentColourless, Pungent--smelling gassmelling gas

-- Only common in alkaline gasOnly common in alkaline gas

-- The molecule is pyramidal in shape due to itsThe molecule is pyramidal in shape due to its

lone pair lone pair



2. In terms of Lewis theory,2. In terms of Lewis theory,

-- Ammonia is a Lewis base because it acts anAmmonia is a Lewis base because it acts an

electronelectron--pair donor pair donor

-- It can form dative bond by donating its lone pair It can form dative bond by donating its lone pair

on the nitrogenon the nitrogen

atom to any Lewis acidatom to any Lewis acid



3. In terms of Bronsted3. In terms of Bronsted--Lowry theory,Lowry theory,

-- Ammonia is a base because it is a protonAmmonia is a base because it is a proton

acceptor.acceptor.

-- It accepts a proton to form an ammonium ionIt accepts a proton to form an ammonium ion

NH NH33 (g) + H(g) + H220 (l) NH0 (l) NH44 (aq) +(aq) +OH (aq)OH (aq)

(Base) (Acid)(Base) (Acid)

(Conjugate (Conjugate(Conjugate (Conjugate

Acid)Acid)



4.4. Ammonia is highly soluble in water producingAmmonia is highly soluble in water producing

a weak base solution with a low basea weak base solution with a low base

dissociation constant (Kb = 1.81dissociation constant (Kb = 1.81 ×× 10 ̂10 ^--5 mol5 moldm^dm^--3).3).

-- Its high solubility is due to hydrogen bondingIts high solubility is due to hydrogen bonding

between ammonia molecules and water between ammonia molecules and water

moleculesmolecules

NH NH33 (g) + H(g) + H22O (l)O (l)

HH33 N.H N.H2200

5. It can react with aqueous acid to form5. It can react with aqueous acid to form

ammonium salts. The unpaired electrons on theammonium salts. The unpaired electrons on the

nitrogen atom can bond with a proton to formnitrogen atom can bond with a proton to form



6. Gaseous ammonia can react as a base towards acidic6. Gaseous ammonia can react as a base towards acidic

gases.gases.

-- when it is reacted with gaseous HCl, white fumeswhen it is reacted with gaseous HCl, white fumes

of ammonium chloride are formed.of ammonium chloride are formed.

-- This is also used a test for the presence of ammoniaThis is also used a test for the presence of ammoniagas.gas.

NH NH33 (g) + HCl (g) NH(g) + HCl (g) NH44Cl (g)Cl (g)

--A dative bond is formed between nitrogen inA dative bond is formed between nitrogen in

ammonia with hydrogen in hydrogen chlorideammonia with hydrogen in hydrogen chloride



7. Ammonia is used as a reagant to identify7. Ammonia is used as a reagant to identify

cations in qualitative analysis. All cationscations in qualitative analysis. All cations

produce metal hydroxides as precipitates except produce metal hydroxides as precipitates except Na+, K+ and NH Na+, K+ and NH44+.+.

8. Some metal hydroxides dissolve in excess8. Some metal hydroxides dissolve in excess

ammonia to produce complexes that are solubleammonia to produce complexes that are soluble

in water. Ammonia acta as ligands in thein water. Ammonia acta as ligands in the

formation of complexes by donating the loneformation of complexes by donating the lone

pair of electrons to the empty orbitals of metal pair of electrons to the empty orbitals of metal

ions.ions.

9. Ammonia can act as a reducing agent in9. Ammonia can act as a reducing agent in

redox reactions. In the process, ammonia willredox reactions. In the process, ammonia will



USES OF AMMONIAUSES OF AMMONIA

1. Manufacture of nitrogen fertilizers (Example:1. Manufacture of nitrogen fertilizers (Example:

Ammonium Sulphate, Ammonium Nitrate, Urea)Ammonium Sulphate, Ammonium Nitrate, Urea)

NH NH33 + HNO+ HNO33 NH NH44 NO NO33 (ammonium(ammonium

nitrate)nitrate)

2NH2NH33 + H+ H22SOSO44 (NH(NH44))22SOSO44 ((

ammonium sulphate)ammonium sulphate)2NH2NH33 + C0+ C022 (NH(NH2)22)2CO (Urea) + HCO (Urea) + H22OO

2. Manufacture nitric acid in the Ostwald rocess2. Manufacture nitric acid in the Ostwald rocess



Ostwald ProcessOstwald Process

* Is the process for producing nitric acid* Is the process for producing nitric acid

Stage 1: Catalytic oxidation of ammoniaStage 1: Catalytic oxidation of ammonia

Ammonia is oxidised by air to nitrogenAmmonia is oxidised by air to nitrogen

monoxide at 850monoxide at 850--900ÛC in the presence of 900ÛC in the presence of

platinum as a catalyst. platinum as a catalyst.

4NH4NH33 (g) + 5O(g) + 5O22 (g) 4NO (g) +(g) 4NO (g) +

6H6H22O (g)O (g)

Stage 2: Oxidation of nitrogen monoxide toStage 2: Oxidation of nitrogen monoxide to

nitrogen dioxidenitrogen dioxide

Nitrogen monoxide, NO is further oxidised by Nitrogen monoxide, NO is further oxidised by



Stage 3: Formation of nitric acid from nitrogenStage 3: Formation of nitric acid from nitrogen

dioxidedioxide

1. Nitrogen dioxide gas dissolves in water to1. Nitrogen dioxide gas dissolves in water toform nitric acidform nitric acid

( 50( 50--60%) and nitrous acid.60%) and nitrous acid.

2NO2NO22 (g) + H(g) + H22O (l) HNOO (l) HNO33 (l)(l)

+ HNO+ HNO22 (l)(l)

2. Nitrous acid, HNO2. Nitrous acid, HNO22 is converted to HNOis converted to HNO33 andand NO on heating. NO on heating.

3HNO3HNO22

(l) HNO (l) + H(l) HNO (l) + H22

O (l) +O (l) +2NO2NO



Overall equation: 4NOOverall equation: 4NO22 + 2H+ 2H22O + OO + O22

4HNO4HNO33

3. Liquid ammonia is used as a cooling agent or 3. Liquid ammonia is used as a cooling agent or refrigerant becauserefrigerant because

of its low boiling point and high latent heat of of its low boiling point and high latent heat of

vaporisation.vaporisation.

4. Liquid ammonia is used as a domestic4. Liquid ammonia is used as a domesticcleaning agent. It is volatilecleaning agent. It is volatile

and does not leave any residue after cleaning.and does not leave any residue after cleaning.

5. Ammonia is used in agriculture industries for 5. Ammonia is used in agriculture industries for essential plant growth.essential plant growth.



QUESTIONS«QUESTIONS«

Ammonia gas can be prepared in a laboratory byAmmonia gas can be prepared in a laboratory by

heating an ammonium salt withheating an ammonium salt with

A. Devarda¶s alloyA. Devarda¶s alloy

B. Hydrochloric acidB. Hydrochloric acid

C. Calcium hydroxide solutionC. Calcium hydroxide solution

D. Acidified solution of potassium manganate (VII)D. Acidified solution of potassium manganate (VII)

Answer:Answer:

C. Calcium hydroxide solution.C. Calcium hydroxide solution.

When an NHWhen an NH4 +4 + compound is heated with acompound is heated with a



Which of the following is true about ammonia?Which of the following is true about ammonia?

A. Ammonia dissolves in water to form NHA. Ammonia dissolves in water to form NH44OHOH

B. Ammonia gas is liberated when ammonium nitrateB. Ammonia gas is liberated when ammonium nitrate

is heated with calcium oxideis heated with calcium oxide

C. Ammonia forms nitrogen dioxide when it reactsC. Ammonia forms nitrogen dioxide when it reacts

with oxygenwith oxygen

D. Ammonia reacts as a Lewis acid in the reactionD. Ammonia reacts as a Lewis acid in the reactionwith copper(II) ion to form a dark blue complex ion.with copper(II) ion to form a dark blue complex ion.

Answer:Answer:

BB



Gases given off from vehicle exhausts affect theGases given off from vehicle exhausts affect the

environment and living things. Which is not the effectenvironment and living things. Which is not the effect

of the gases?of the gases?

A. Acid rainA. Acid rain

B. Chemical corrosionB. Chemical corrosion

C. Toxicity of the bloodC. Toxicity of the blood

D. Thinning of the ozone layer D. Thinning of the ozone layer

Answer:Answer:

DD



4.3 OXIDES OF NITROGEN

NO

NO2

N2O4



NITROGEN MONOXIDE

Is prepared by the action of copper on hot,50% nitric (v) acid.

3Cu(s) + 8HNO3(aq)3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)

Is a colourless gas, but forms brown fumes of nitrogen oxides if contacted with air.

2NO(g) + O2(g) 2NO2(g)



Is only very slightly soluble in water.

The structure of nitrogen monoxide is a resonancestructure of two forms.

Is purified by absorption into aqueous iron(ll) sulphate where abrown solid is formed.

FeSO4(aq) + NO(g) FeSO4NO(s)



Heating the solid in the absence of air regenerates the

nitrogen monoxide.

FeSO4NO(s) FeSO4(s) + NO(g)



NITROGEN DIOXIDE

Is produced by the action of heat on thenitrate(v) of heavy metals.

2Pb(NO3)2(s) 2PbO(s) + 4NO2(g) + O2(g)

eg.

Can also be produced by the reaction of copper on hotconcentrated nitric(v) acid.

Cu(s) + 4HNO3(aq) Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)



DINITROGEN TETR AOXIDE

It is formed when a sample of nitrogen dioxide iscooled.It dimerises to form a colourless dimer,N2O4

2NO2(g) cooling N2O4(g)

Exists as a colourless solid at temperature below -11C .

The solid melts to a pale yellow liquid when heated.When the temperature increases, the colour of thesolution gets deeper and turns into a reddish-brownvapour.



POLLUTION CAUSED BY NITRIC OXIDE

Considered as a primary air pollutant.

The environmental sources of nitric oxide are:

Burning of fossil fuels containing nitrogencompounds. Reaction between nitrogen and oxygen in internalcombustion engines at high temperatures. Lightning which combines the atmosphericnitrogen and oxygen.

Causes pollution:

It dissolves in rainwater to form nitrous acid and nitric acid wherethese are considered as a secondary pollutant. It will tend to combine with gaseous hydrocarbons in the atmosphereto form smog.



QUESTIONS....

1.Nitrogen oxides have high positive standard enthalpies of formation . Which of the following is the major for the high positive value of ?

A. The tendency of oxygen to form oxides.B. The high electron affinity of the oxygen atom.

C. The nitrogen and oxygen atoms have similar electronegativities.D. The high bond energy of the N2 molecule.

Ans : D

A lot of energy must be supplied to break the N bonds to form N atoms.Energy is liberated when N-O bonds are formed.Energy absorbed on bond breaking > energy liberated on bond formation.Hence,

of nitrogen oxides are highly endothermic.



2.Nitrogen is an unreactive element becausei.its enthalpy of atomisation is highii.its bond energy is highiii.it is a non-polar molecule

Ans: all correct.

3.Oxides of nitrogen are produced by the reaction betweeni.nitrogen and oxygen in internal combustion engines.ii.nitrogen and oxygen during lightning.iii.ammonia and oxygen in the presence of heated platinum metal

Ans: all correct



THE END... THANK YOU FOR LISTENINGTHE END... THANK YOU FOR LISTENING

group 15 - nitrogen

Documents