Making Crystals
1.
Dissolving a solid in water or any other
solvent and then evaporating the liquid. For example, salt, nitre, alum in
water. Sulfur in carbon disulphide or carbon tetrachloride CCl4, iodine
in petrol or benzene or spirit.
2.
By melting a solid and allowing it to cool
properly. For example, prismatic sulfur.
3.
By sublimation. For example, iodine and
ammonium crystals.
4.
By subjecting a solid to great heat and
pressure. For example, diamond and graphite. The cost is prohibitive as
artificial diamond is more costly than natural diamond.
Water of Crystallization
Some solids while crystallizing
out from solution unite with a definite quantity of H2O known as
water of crystallization/ hydration. This water of crystallization can be
driven out by heating the crystal to 100°C, and may be condensed and tested.
Such crystals lose their crystalline structure and become anhydrous.
Water of crystallization is the number of molecules of water combined it a loose chemical
combination which on heating on exposure to air is partly on fully given off by
a hydrated salt.
Hydrated Salts
A hydrated salt is a substance
which contains water of crystallization which on exposure to air or heat becomes
anhydrous by giving off partly or fully its water of crystallization.
Hydrated
Salt
|
Chemical
Formula
|
Common
Name
|
sodium carbonate
|
Na2CO3 · 10H2O
|
washing soda
|
sodium sulphate
|
Na2SO4 · 10H2O
|
Glauber’s salt
|
copper sulphate
|
CuSO4 · 5H2O
|
blue vitriol
|
ferrous sulphate
|
FeSO4 · 7H2O
|
green vitriol
|
zinc sulphate
|
ZnSO4 · 7H2O
|
white vitriol (H2SO4
is called oil of vitriol)
|
cobalt chloride
|
CoCl2 · 6H2O
|
|
barium chloride
|
BaCl2 · 2H2O
|
|
calcium chloride
|
CaCl2 · 6H2O
|
|
magnesium sulphate
|
MgSO4 · 7H2O
|
Epsom salt
|
Crystals without Water of
Crystallization – Anhydrous
Anhydrous
Salt
|
Chemical
Formula
|
sodium chloride (common salt)
|
NaCl
|
nitre
|
KNO3
|
potassium chromate
|
K2C5O7
|
potassium chloride
|
KCl
|
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