About Gravimetry

2. introduction
The substance to be determined by converting in to pure
chemical compound then weighed.
For conversion of compound to pure compound to
follow various technique.
Eg: Precipitation methods by precipitating agent.
Volatilisation methods or ignition
Electro gravimetry
Thermo gravimetry.
The substance to be measured at the pure from without
chemical change by gravimetry.

3. ADVANTAGE
It is accurate and precise.
Possible source of error and readily checked.
To involve direct measurement of substance.
Need only inexpensive apparatus.

4. It is process to isolating and weighing an pure
compound from the element. The separation
of the element or the compound by following
ways:
1.Precipitation methods
2.Volatilisation - ignition or drying.
3.Electro gravimetry.

5. Weighed quality of sample dissolved in suitable solvent to
solution form.
Precipitated by precipitation agent
Filter –dried – weighed – calculate the % of content.

6. To remove the volatile substance.
It is carried out by:
1. By simple ignition in air
2. By treating with chemical agent to get
volatile substance.
3. By treating with chemical agent to get non
substance.
The volatilised substance absorbed by suitable
medium then weighed. (or) the weight of residue
after volatilisation is determined .

7. ELECTRO GRAVIMETRY
he substance is deposi ted electrolyt ical ly
to sui table electrode then f i l ter most ly i t
used to est imate.

8. THERMOGRAVIMETRY
To keep both sample and returns them apply thermal power.
The measure what are the changes occuring in both sample and
reference.
VARIOUS STEPS INVOLVED IN GRAVIMETRIC
ANALYSIS :
 To follow following steps:
Precipitation, Filteration, washing of the precipitate
Drying or ignition of the precipitated.

9. PRECIPITATION
Precipitation are usually made by using beakers.
Beakers is covered by clock glass.
To add precipitating reagent (by using pipette or burette) by
slowly with sufficient stirring.
To avoid the splashing by adding precipitating at moduate speed.
The stirring rod should not touch the surface or walls of the
beaker.
Then allow the percipitate settle overnight or by heating the
precipitate.
To reduce the coarseness of the precipitate.
Filter
Collect the precipitate

11. SURFACE ADSORPTION
By using surface adsorption process to get
the co-precipitation.
eg: coagulated colloids.
The reaction between AgNo3 in
determination chloride ion to get Agcl as
colloids and also the silver ions adsorbed with
nitrate or other anions.

12. It is type of co-precipitation. The contaminate ion
replaced by ion containing crystal.
Eg: Barium sulphate formed by adding Bacl2 to a
solution containing sulphate, lead, and acetate.
The co-precipitation is the lead ion replaces the barium
ion in Baso4 to get lead sulphate as co-precipitation.

13. When crystal is growing rapidly during precipitation
the formation is affected by mechanical entrapment or
pressure disturbance.
Digestion process is helpful to avoid the co-precipitation
process.

14. The precipitation and occurs on the
surface of the first precipitation after its
formation.
Eg: Formation of calcium as calcium
oxalate in the presence of magnesium, but
it produce presence of magnesium oxalate
gradually, but it produce error in
determine.
Eg: Mercury II sulphide in 0.3m Hcl in the
presence of zn ions but later your get zinc
sulphide precipitation.

15. Difference between co-precipitation
and post precipitation:
1. The contamination or impurities is in post
precipitate.
2. But co-precipitate
3. The contamination increases in post precipitate
by (mechanical or thermal process.) digestion
but in co-precipitate-contamination is
4. The magnitude of contamination by post
precipitate much be greater in co-precipitate.

16. To separate the precipitate by using
filteration process.
Filter paper, sintered crucible or
gooch crucible.
FILTER PAPER:
Ashless filter paper
Whatmann filter paper.

17. 1.Gooch crucible either porcelaim or silicon in
avaliable market.
2.Sintered glass or silica crucibles.
GOOCH CRUCIBLES:
Perfoated
plate
Asbestos
pad
Particular
pore
Size plate
Gooch
crucibles
flask

18. 1. Moisken the filter paper
2. Keep the precipitate in central portion of mat
3. Pour the liquid slowly with continious stirring
4. Add about 10-20ml of liquid and allow to stand for
settling of precipitate.
5. To repeat this procedure 3 or 4 times.
Drying:
After washing the precipitate containing definite
composition of compound and dried at specified as
per description. But nowdays ovens with thermo
regulator available. Eg: for formulation:
amodiaquine Phenobarbitone tablet.

19. The dilute solution of barium chloride
added slowly to sulphate ion to get Baso4 as
precipitate.
The precipitate is filtered,washed H20.
Ignite and weighed as BaSo4.

20. Procedure:
0.3g of substance
1.25 ml H2O + 0.3 -0.6 ml CON Hcl dilute to
225ml.
heat – dropwise add 10-12ml of BaCl2.
stir check the precipitate by adding 1-2 ml
of BaCl2 keep at 1hr/hot condition filter
collect dried weigh
wash

21. DETERMINATION OF CALCIUM AS
CALCIUM OXALATE:
The calcium is precipitited as calcium oxalate by
treating c hot Hcl c ammonium oxalate and slowly
neutralising c ammonia.
the precipitate is washed c dilute ammonium
oxalate then weighed.
0.2 gm of cal +10 ml H2O + 15 ml of dil Hcl
Dil to 200 ml add 2gm of ammonium oxalate
and ammonium up to making alkaline filter
collect the precipitate wash dried.

22. Now days heating crucibles also available
finally to keep the substance at dessicator.
THERMO ANALYTICAL METHODS:
To analyse the substance according to
temperature.
TGA- thermo gravimetric analysis-weight loss
DTG-derivative thermo gravimetric –analysis
DTA-differential thermal analysis-tempt
DSC-differential scanning calorimetry-enery
input

23. THERMO GRAVIMETRIC CURVE
To draw the graph b/w temperature vs % wt loss
to get thermo gravimetric curve.
Eg: CuSo4.5H2o CuSo4 (90-150 c)
CuSo4.H2O CuSo4 (200-275 c)
CuSo4 Cuo + So2 + ½ O2 (700-900 c)
2Cuo Cu2o + ½ O2 (1000-1100 c)