GRAVIMETRIC METHOD Flashcards
consists of isolating
from the sample the constituent to be
determined in its pure state and weighing it
accurately
Gravimetric analysis
Isolation may be done by:
❖ precipitating the sought substance in an
insoluble form
❖ electrolysis
❖ converting the substance to a gas which is
absorbed in a suitable reagent.
MANIFESTATIONS OF PRECIPITATION
- Of low solubility
- Large in particle
- Easily filtered
- Pure and stable
The ionic product exceeds the solubility product
constant, precipitation will occur
Solubility Product principle
The ionic product exceeds the solubility product
constant, ______ will occur
precipitation
If there is an excess of one ion over the other, the
solubility of the precipitate will decrease
The common ion effect
If there is an excess of one ion over the other, the
solubility of the precipitate will _____
decrease
The rate of the reaction is directly proportional to
the product of the molecular concentrations of the
reacting substance
Law of mass action
The rate of the reaction is directly proportional to
the product of the ____ of the
reacting substance
molecular concentrations
Gravimetric method by
precipitation
❖ Dissolve sample
❖ Add ppt’ing reagent
❖ Filter
❖ Dry
❖ Weigh
ASSAY OF SODIUM SULFATE
- 500 mg sample dissolved in 150 mL dw
- Add 12 mL conc HCl
- Pour 20 mL BaCl 2
- Stand
- The supernatant liquid is decanted and the precipitate is washed three
times with warm water. The residue is white. It is then cooled and
weighed
Compute for the gravimetric
factor
GF = MW sought/MW ppt
Compute for the weight of
pure substance
% = Wt ppt X GF x 100/Wt sample
The residue weighed
must have a ______
DEFINITE
CHEMICAL
COMPOSITION
And bears a _____ with the
constituent to be
determined
DEFINITE
RELATION
