ICSE CHEMISTRY
Salt:
A compound formed by the partial or complete
replacement of replaceable Hydrogen ions of an acid by a metal ion or Ammonium
ion.
H2SO4 + NaOH -->
Acid salt
H2SO4 + 2NaOH -->
Na2SO4
+ H2O complete replacement
of Hydrogen ions
Normal salt
HCl + Ca(OH)2 -->
Ca(OH)Cl + H2O partial replacement of hydroxyl ions
Basic salt
Classification
of salts:
Normal salt
|
Acid salt
|
Basic salt
|
1.
It is formed by the complete neutralization of an
acid by a base i.e. complete replacement of Hydrogen ions of an acid by metal
ion or Ammonium ion.
2.
Normal salt is neutral in nature.
example: NaCl,
Na2SO4, MgCl2 etc.
|
1.
It is formed by the partial neutralization of an
acid by a base i.e. partial replacement of Hydrogen ions of a dibasic or tri
basic acid by metal ion or Ammonium ion.
2.
Acid salt is acidic in nature due to the presence
of Hydrogen ions.
example : NaHSO4,
NaHCO3, NaH2PO4, Na2HPO4
etc.
|
1.
It is formed by the partial replacement of
Hydroxyl ions of a di acidic or tri acidic base by an acidic radical.
2.
It is alkaline in nature because it contains hydroxyl
ions.
example :
Ca(OH)Cl, Cu(OH)Cl etc.
|
Examples of complex salts:
K2HgI4 – Nesseler’s reagent
Na[Ag(CN)2] – Sodium silver cyanide
[Cu(NH3)4]SO4 –
Tetrammine Copper[II] sulphate
Solubility
of salts in water
Soluble salts
|
Insoluble salts
|
-
All Na, K and Ammonium salts
-
All Bicarbonates
-
All sulphates
-
All chlorides
-
All nitrates and nitrites
v Sulphides,
Sulphites, carbonates, oxides, hydroxides, phosphates of Na, K and ammonium
salts are soluble
|
-
KHCO3 and NaHCO3 are
partially soluble
-
PbSO4, AgSO4, CaSO4,
BaSO4
-
AgCl, HgCl, PbCl2( soluble in hot
water)
-
All sulphides, sulphites, carbonates
-
All oxides, hydroxides, phosphates
|
Preparation
of salts:
1. Neutralization
:
An insoluble
base + a dilute acid
A soluble salt + water
CuO + H2SO4 -->
CuSO4 + H2O
Black blue
solution
PbO + 2HNO3 -->
Pb(NO3)2 + H2O
Soluble
Pb(OH)2
+ 2HNO3
---> Pb(NO3)2 + 2H2O
- Decomposition
of insoluble metal carbonates by dil. acids.
PbCO3
+ 2HNO3
--> Pb(NO3)2 + H2O + CO2
CuCO3
+ H2SO4 -->
2.
Neutralization (titration):
A soluble base +
an acid
soluble salt + water
NaOH + HCl -->
NaOH + HNO3 -->
- Decomposition
of soluble metal carbonates by dil. acids.
Na2CO3
+ H2SO4 -->
3.
Simple displacement:
Active metal +
dil.acid
metal salt + Hydrogen gas
Fe + 2HCl -->
FeCl2 + H2
Zn + H2SO4 -->
ZnSO4 + H2
4.
Direct combination:
Metal + Non
metal -->
2Fe + 3Cl2 -->
2FeCl3
(soluble salt)
Fe + S -->
Zn + S -->
5.
Double decomposition:
Pb(NO3)2
+ 2NaCl -->
Soluble insoluble
ZnSO4
+ (NH4)2CO3 -->
Soluble insoluble
CaCl2
+ Na2CO3 -->
æ The
soluble salts are separated by evaporation or distillation of the salts
solutions.
æ The
insoluble salts are filtered and dried.
Preparation of Ferric chloride or Iron (III)
chloride (FeCl3) :
æ Ferric
chloride vapours are solidified using freezing mixture. A drying agent CaCl2
is used to absorb moisture since FeCl3 is deliquescent in nature.
ü Water of crystallization:
When a water soluble salt is obtained by the crystallization of its aqueous
solution each molecule of a salt holds a definite number of water molecules
with a weak chemical bond. This amount of water is called water of
crystallization.
ü Hydrated salt:
The salt which contains a definite number of water molecules is called a
hydrated salt.
Example:
CuSO4.5H2O
MgSO4.7H2O
Na2CO3.10H2O
ü The
salt which has no water molecules is an anhydrous salt. CuSO4.
ü Deliquescent salt: It is a water soluble
crystalline salt which absorbs moisture from the atmosphere and turns into a
saturated solution.
Example: FeCl3,
CaCl2, MgCl2, ZnCl2, Fe(NO3)3,
Cu(NO3)2 etc.
When
FeCl3 is exposed to the atmosphere it absorbs water and forms its
aqueous solution.
ü Efflorescent salt:
It is a crystalline hydrated salt which loses(partly or completely) its water
of crystallization to the atmosphere and becomes a powder.
Example: CuSO4.5H2O
MgSO4.7H2O
Na2CO3.10H2O
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