INORGANIC CHEMISTRY

MEGA-XII

HEATING EFFECTS
INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)
HEATING EFFECTS
General Thermal decomposition reaction of metal carbonate salts
R.T.
H2CO3 (carbonic acid)  H2O + CO2(g) (Non redox reaction)

Metal carbonate   M2Ox(solid) + CO2 (g)

Except: M2CO3 (M+ = Na+, K+, Rb+, Cs+) 

  do not decompose but melt at high temperature.

Li2CO3   Li2O + CO2 (g)
D.R.

MgCO3   MgO + CO2 (g)

ZnCO3   ZnO (Philosopher’s wool) + CO2 (g)

PbCO3   PbO (Litharge) + CO2 (g)

CaCO3 
1000C
 CaO + CO2 (g)

2PbCO3.Pb(OH)2(white lead)   3PbO(Litharge) + 2CO2(g) + H2O

CuCO3.Cu(OH)2(Green Malachite)   2CuO (Black) +CO2(g) + H2O

Ag2CO3 
300C
 CO2 (g) + Ag2O 300C
  2Ag + [O] nascent oxygen / ½O2(g)
 Strong oxidising agent 

Ag2CO3 
300C
 2Ag + CO2 (g) + [O] nascent oxygen / ½O2(g)

  400C
HgCO3 
 400C
 CO2 (g) + HgO   Hg + CO2 (g) + [O] nascent oxygen / ½O2(g)

OR 
HgCO3  Hg + CO2(g) + ½O2 / nascent oxygen [O]
Important Points :
• When oxysalt of noble metals (Ag, Au, Hg, Pt) are heated, then initially noble metal oxide is formed which
being thermally less stable are further decomposed into noble metal and oxygen on moderate heating
(flame temperature). In this way, they act as strong oxidising agent.

Ag2O (Brown) 
T 300C
 2Ag + ½O2 / [O]
Strong 
oxidising HgO (Yellow) 
T  400C
 Hg + ½O2 / [O]
agent

PbO2 (Brown) 
T 500C
 PbO (Litharge)+ ½O2 / [O]

General thermal decomposition reaction of metal sulphate salts

444 º C
H2SO4 (sulphuric acid)    H2O + SO3(g) (Non redox reaction)

 
Metal sulphate 
T 800C
 M2Ox (solid) + SO3 (gas)  
T 800C
 SO2  + ½O2


Except : M2SO4 (M+ = Na+, K+, Rb+, Cs+)   do not decompose but melt at high temperature like
carbonate salts.

Li2SO4 
T 800C
 Li2O + SO3 (g)
D.R.

MgSO4 
T 800C
 MgO + SO3 (g)

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)

CaSO4 
T 800C
 CaO + SO2 (g) + ½O2 (g)


ZnSO4 
T 800C
 ZnO (Philosopher’s wool) + SO2 (g) + ½O2 (g)

PbSO4 
T 800C
 PbO (litharge) + SO2 (g) + ½O2 (g)


HgSO4 
T 800C
 Hg + O2 (g) + SO2 (g)


Ag2SO4 
T 800C
 2Ag + O2 (g) + SO2 (g)

120C 120C T 800C

CaSO4 • 2 H2O 
 3/2 H2O
 CaSO • ½H O   CaSO4 (anhydrous)   CaO+SO3(g)
4 2

(Gypsum) Plaster of paris (POP) dead burnt plaster > 800ºC

CaO + SO2(g)+ ½O2 (g)

250C 750C 1100ºC 1

CuSO 4  5H2O  5H2 O
 CuSO4   SO3 (g)  CuO   Cu2 O(more stable)
 Black  2
 blue vitriol  amorphous
 white solid 
 Non redox reaction
ZnSO4  7H2O 
7H O
 ZnSO4 
T  800C
 ZnO  SO3  g 
2
 white vitriol anhydrous; Philosopher ' s wool
amorphous
withe solid

Non redox reaction

Fe2(SO4)3  T     Fe O + 3SO (g)
800 º C 2 3 3

RA OA Intramolecular 3 4 6
300C redox reaction
FeSO 4  7H2O   FeSO 4   Fe2 O3  S O2   S O3 
7H O
 Green vitriol
 from 2 moles 
2
anhydrous; Brown solid 
T 300C Bothoxides of sulphur evolved.
amorphous
withe solid simul tan eously

RA OA

2Cr SO 4 
Intramolecular
 Cr2O3  SO 2  SO3
redox reaction  Green solid

RA OA
2 6

SnSO4 
Intramolecular
 SnO2  SO2
 Tin  sulphate  redox reaction

General thermal decomposition of metal nitrate salt

 5
T  40 º C
HNO3(Nitric acid) 
 H2O + N2O5   2NO2(g) + 1/2O2(g)
T 40 º C
+5
 T>40°C
Metal nitrate salt M2Ox(solid) + N2O5 2NO2 (g) + ½O2 (g)


Metal oxide + 2NO2 (g) + ½O2(g)
Except nitrate salt of MNO3 : (M+ : Na+, K+, Rb+, Cs+)
metal nitrite 
500C 800º 3
MNO3   ½O2  MNO2 M2O  N2  O2
Metal nitrate   from 2 mol 2
(M+ : Na+, K+, Rb+, Cs+)

4

2LiNO3   Li2O + 2NO2 (g) + ½ O2(g)
Brown gas 
D.R.
4

Mg(NO3)2   MgO + 2NO2 (g) + ½O2 (g)
Brown gas 

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)
4

Ba(NO3)2   BaO + 2NO2 (g) + ½O2 (g)
4

Zn(NO3)2   ZnO (Philosopher’s wool) + 2NO2 (g) + ½O2 (g)
4

Pb(NO3)2   PbO (litharge) + 2NO2 (g) + ½O2 (g)

2AgNO3   2Ag + O2 (g) + 2NO2

Hg(NO3)2   Hg + O2(g) + 2NO2 (g)
General thermal decomposition reaction of metal acetate salt

2CH3COOH CH3COCH3 + H2CO3(H2O + CO2)
(acetic acid) acetone
 Metal carbonate (Stable at flame temp.)
Metal acetate salt CH3COCH3 +
inflammable OR
(MO + CO2) if metal cation with high  value
+ 2+ 3+ 2+
like with Li , Mg , Al , Be cations and all
p & d-block cations.
OR
(M + 1/2 O2 + CO2) with noble metals.

Except : 
CH3COOM CH3COCH3 + M2CO3 (don't decompose)
+ + + + +
(M =Na ,K ,Rb ,Cs )


2CH 3COOK CH 3COCH3 + K2CO 3

Ca(CH3COO)2 CH3COCH3 + CaCO3

Ba(CH3COO)2 CH3COCH3 + BaCO3

Be(CH 3COO)2 CH 3COCH3 + BeO + CO 2

Mg(CH3 COO)2 CH 3COCH3 + MgO + CO 2

Pb(CH 3COO)2 CH 3COCH3 + PbO + CO 2

Zn(CH3COO)2 CH3COCH3 + ZnO + CO2

Hg(CH3COO)2 CH3COCH3 + Hg + 1/2 O2 + CO2

2CH3COOAg CH 3COCH3 + Ag + 1/2 O2 + CO 2

General thermal decomposition reaction of metal oxalate salt


H2C2O4 (oxalic acid)  CO + H2CO3 (disproportionation reaction)

 Metal carbonate (Stable at flame temp.)

Metal oxalate salt CO +
inflammable OR
(burns with (MO + CO2) if metal cation with high  value
blue flame) + 2+ 3+ 2+
like with Li , Mg , Al , Be cations and all
p & d-block cations.
OR
(M + 1/2 O2 + CO2) with noble metals.

Except : 
M2C2O4 M2CO3 + CO2 + CO+ carbon
+ + + + +
(M = Na ,K ,Rb ,Cs )

Eg. CaC2O4  CO + CaCO3 (Decomposes above 1000ºC))

BeC2O4  CO + BeO + CO2

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)

PbC2O4  CO + PbO + CO2

ZnC2O4  CO + ZnO + CO2

HgC2O4  Hg + 2CO2

Ag2C2O4  2Ag + 2CO2

FeC2O4  FeO + CO2 + CO (CO gas prevent air oxidation of FeO)
Ferrous oxalate O2(Air)

Fe2O3


SnC2O4 SnO + CO2 + CO (CO gas prevent air oxidation of FeO)
Tin oxalate O2(Air)

SnO2

General thermal decomposition of metal bicarbonate salts

Metal bicarbonate salt 
  Metal carbonate salt + CO2 + H2O

2M HCO3 (M+ : Na+, K+, Rb+, Cs+)  M2CO3 + CO2 + H2O

Only bicarbonate salts existing in solid state.

In general; remaining bicarbonate exist in solution form, where crystallisation is not possible due to
uncomparable size of bicarbonate ion & metal cation.
T 100C
2HCO3 (aq) 
Boil CO32– (aq)  CO2   H2O (This reaction is used to remove temporary hardness of water)

LiHCO3 and Mg(HCO3)2 exist in solution form. Their crystallisation is not possible due to uncomparable size
of cation and anion. (Diagonal relationship)

Thermal Decomposition of 1°, 2° and 3° phosphate salts s-block metals :

H  H  
H

H3PO 4  
 H2PO 4  
  HPO 4 2
 
 
 PO 43 
Phosphoric 1 Phosphate ion 2Phosphateion 3Phosphate ion
acid


NaH2PO 4 
H O NaPO3  H2O
2
1 Phosphate salt


2Na2HPO 4 
H O Na 4P2O7  H2 O
2
2Phosphate salt


Na3PO 4   No decomposition
3Phosphate salt (Thermally stable)

2NH 
NaH2PO 4 3
  Na(NH4 )2 PO 4   NaPO3  H2 O  2NH3
(1 Phosphate salt) (1 Phosphatesalt)


NaNH4.PO4.4H2O NaNH4.HPO4 NaPO3 + H2 O + NH3
H2O
(Microcosmic salt) (1° Phosphate salt) (Sodium meta
[It is used in detection of phosphate)
cations in qualitative analysis (used in bead test)
in phosphate bead test]

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)
Heating effect of ammonium salts
(a) If anionic part is strong oxdising agent (like Cr2O72–, NO2–, NO3–, ClO4– etc.), then N2 will be

the product (Except NH4NO3  N2O gas).

(NH4)2Cr2O7 Intra
   N  + Cr O + 4H O + Heat (volcanic Reaction)
mol. Re dox 2 2 3 2

orange green

NH4NO2 Intra
     N  + 2H O
mol. Re dox 2 2


NH4NO3 Intra
  N O  + 2H O
mol. Re dox 2 2

2NH4 ClO4 Intra
  N  + Cl  + 2O  + 4H O
mol. Re dox 2 2 2 2

2NH4 IO3  Intra
     N
mol. Re dox 2  + I2  + O2  + 4H2O

(b) If anionic part weakly or non oxidising in nature, then NH3 and coresponding acid will be
the product.

NH4Cl NH3  + HCl  (leaves no residue on heating)
non-redox

(NH4)2S 2NH3  + H2S  (leaves no residue on heating)
non-redox


(NH4)2SO4 2NH3  + H2SO4
non-redox


(NH4)2CO3 2NH3  + H2CO3
non-redox


(NH4)2C2O4  2NH3  + H2C2O4

(NH4)2HPO4  2NH3  + H3PO4

(NH4)3PO4  3NH3  + H3PO4

Heating effect of Oxide salts

Hot

2Ag2O  4Ag + O2 ; ZnO ZnO
Brown 300ºC white yellow
Act as strong Oxidizing
agent due to tendency Cold
to librate O2 on 
2HgO  2Hg + O2
yellow 400ºC
moderate Heating Hot


PbO2  PbO + 1 O2 ; PbO
litharge(Red)
PbO
massicot(yellow)
Brown 500ºC 2
(St. O.A.)
Cold

500ºC

3MnO 2 900
 C
 Mn3O4 + O2  ; Pb3O4
Black 3PbO + 1/2O2
Air
350ºC
1100 º C
2CuO (Black)   Cu2O(Red) + 1/2 O2
(Thermally more stable)

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)
127ºC

2CrO5
R.T.
 Cr2O3 +
7
O2 ; (scarlet Red) Hgl2 Hgl2(yellow sublimate)
aq. so ln .
Blue compound green 2
Unstable
in aq. solution
Rubbing

5
I2O5  I2 + O (used in estimation of CO by Iodometry titration)
2 2

Heating effect of '-ic' form of Oxy Acids

30 ºC 40 º C
conc. 2HNO3   H2O + N2O5   2NO2 + 1/2 O2 or [O]

40 ºC
conc. 2HNO3  2NO2 + H2O + 1/2 O2 or [O]

conc. H2SO4 444

 C
 H2O + SO3

conc. H2SO4 

800C
 H2O + SO2 + + 1/2 O2 or [O]

220 ºC 320 ºC 320 ºC

conc. 4H3PO4    2H4P2O7   (HPO3)4(s)   P4O10(s) + 2H2O
– 2H2O – 2H2O – 2H2O

orthophosphoric acid Pyrophosphoric acid metaphosphoric acid

150ºC Re d
conc. H3BO3 100
 C
 4HBO2  H2B4O7 
 H2O + 2B2O3
hot
orthoboric acid Metaboric acid TetraBoric acid BoricAnhyd

Heating effect of '-ous' form of Oxy Acids


3H2SO3 (conc.)  2H2SO4 + S + H2O


3HNO2 (conc.)  HNO3 + 2NO + H2O


HClO3(conc.)  HClO4 + ClO2 + H2O
Undergoes

3HOCl (conc.)  2HCl +HClO3 disproportionation
reaction

4H3PO3 (conc.)  3H3PO4 + PH3
200C


2H3PO2 (conc.)  H3PO4 + PH3 


H2C2O4 (conc.)  H2O + CO + CO2

Heating effect of Halides salts


2FeCl3  2FeCl2 + Cl2

Hg2Cl2  HgCl2 + Hg

AuCl3  AuCl + Cl2
50 ºC Warm
PbCl4     PbCl2 + Cl2 [PbBr4   PbBr2 + Br2 & PbI4 does not exists]

Pb(SCN)4  Pb(SCN)2 + (SCN)2(Thiocyanogen)

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INORGANIC CHEMISTRY V.K. JAISWAL(VKJ SIR)
spon.
CuI2   CuI + 1/2 I 
R.T. 2

white
spon.
Cu(CN)2   CuCN + 1/2 (CN) (cyanogen)
R.T. 2

white

Heating effect of hydrated chloride salts

 
6H2O + MgCl2 (Anhydrous)   MgCl2 ·6H2O    MgO + 2HCl + 5H2O
HCl gas Hydrolysis


12H2O + 2FeCl3 (Anhydrous)   2FeCl3 ·6H2O  Fe2O3 + 6HCl + 9H2O
HCl gas Hydrolysis

 
12H2O + 2AlCl3(Anhydrous)   2AlCl3 ·6H2O    Al2O3 + 6HCl + 9H2O
HCl gas Hydrolysis

58C
CoCl 2 .6H 2 O 50
C
 CoCl 2 .4H 2 O  CoCl 2 .2H 2 O 140
 C
 CoCl 2
 2 H 2O blue 2 H 2 O Red violet  2 H 2O Blue
Pink

Hydrated Co2+ salt - Pink ; Anhydrous Co2+ salt - Blue

Heating effect of dichromate & permanganate salts


2K 2Cr2O 7  2K 2 CrO 4  Cr2 O3 + 3/2 O2
500º C
Orange Yellow Green


2KMnO 4   K 2MnO 4  MnO2  O2 
Purple 200ºC Green Black

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