Save
Gravimetric
cont.
Save
Share
Learn
Content
Leaderboard
Learn
Created by
jade
Visit profile
Cards (17)
Mass spectrometer
Used to separate
gases
formed from the
elements
making up a complex matter
Precipitates
Large particles are more suitable for
gravimetric
work because they are easier to
filter
and give a purer product than fine particles
Factors that determine the particle size of precipitates
Colloidal
dispersion
Crystalline
suspension
Colloidal dispersion
Particles visible to the naked eye (10 to 10^-6 cm in diameter), difficult to
filter
, show no
tendency
to settle from solution
Crystalline
suspension
Tend to settle
spontaneously
, easily
filtered
Relative supersaturation
Q/S, where Q is the
concentration
of the solute at any instant and S is the
equilibrium solubility
Mechanism of precipitate formation
1.
Nucleation
2.
Particle growth
Colloidal precipitates
Too small to be retained by
filters
Peptization
of
colloids
The process by which a coagulated colloid
reverts
to its original
dispersed
state
Crystalline
precipitates are generally more easily
filtered
and purified than pre-coagulated colloids
Types of
coprecipitation
Surface adsorption
Mixed crystal formation
Occlusion
Mechanical entrapment
Surface adsorption
A process in which normally
soluble
compounds are carried out of solution by a
precipitate
Mixed crystal formation
One of the
ions
in the crystal
lattice
of a solid is replaced by an ion of another element
Occlusion
A type of coprecipitation in which a compound is trapped within a
pocket
formed during
rapid crystal growth
Mechanical entrapment
Occurs when crystals lie close together during
growth
Coprecipitation
effects are at a minimum when the rate of precipitate formation is
low
, that is, under conditions of low supersaturation
Homogeneous precipitation
A process in which a
precipitate
is formed by
slow
generation of a precipitating reagent