An overall description of all operations in gravimetric analysis

1. By
Sruthi sudhakar
Chemistry batch 2013-16
Sir syed college
Kannur
kerala

2. So let us begin
So let us
begin…

3. analysis
Qualitative: composition
Quantitative: amount

4. Quantitative analysis
Volumetric analysis
Gravimetric analysis

5. Gravimetric analysis

6. Gravimetric analysis
Analysis by weight
The process of isolating and weighing an
element or a defenite compund of the element
in as pure form as possible
Element transformed to stable form for
weighing
Weight calculated from knowledge of
formula of compound and relative atomic
masses

8. Unit operations in gravimetry
 Preparation of sample solution
 Precipitation
 Digestion
 Washing
 Filteration
 Drying
 Weighing and calculation

9. Sample preparation
• Dissolved if not in solution
• Made upto the volume we need
• Ph is adjusted

10. precipitation
Process of formation of a solid in solution
during a chemical reaction.
Precipitation reaction can be used for making
chemicals removing salts from water…etc

11. Process in precipitation
• Nucleation
Ions join
Seeding- induced nucleation
• Crystal growth
Diffusion to nucleus
Deposition on surface

12. Ions of opposite charge are attracted to the region of the solution
surrounding the particle. These ions are called counter ions.

13. • Precipitating reagent is added
• Checked if precipitation is complete

14. Conditions of precipitation
• Precipitation in dilute solution
• Slow addition of reagent
• Reagents mixed with constant stirring
• High temperature
o Solubility increased but degree of supersaturation
decreased
o Velocity of crystallisation increased
o Coagulation is assisted

15. • Crystalline precipitate digested as long as
possible
• Precipitate washed with electrolyte
• Relative supersaturation must be decreased

17. Theory of precipitation
• Ionic product and solubility product
• P<Ksp no precipitation
• P> Ksp precipitation

18. GOOD PRECIPITATE
• Non-amorphous precipitate
• Will redissolve, if given the right
conditions
NOT DESIRABLE PRECIPITATE
• Characteristic brownish tinge to the
precipitate
• Do not redissolve upon dilution

19. Organic precipitants
 The chelate compound obtained by the reaction between
metal ions and organic precipitant are generally highly
soluble
 Molecular weights of organic pecipitants are generally
high.Hence, the molecular weights of the corresponding
chelate compounds are also high.Thus, even a small amount
of metal gives relatively greater amounts of precipitates
 Many organic precipitants are quite selective-they form
chelate compounds with only a few.
 The precipitants obtained with organic precipitants are made
of coarse particle which can be easily filtered.
_

20. 1) DMG ------------------------------Ni
2) 8-hydroxy quinoline-------------Al
3) α-nitroso, β-naphthol-----------Co
4) Cupferron-------------------------Fe
5) α-benzoinoxime or Cupron----Cu

21. Purity of precipitation
• Co precipitation
Occlusion
Surface adsorption
• Post precipitation

22. Points to remember
• Precipitation must be complete
• Weighed from must be stable
• Product must be pure
• Rate of reaction fast
• Precipitate large to settle down
• Precipitate dry and stable upon ignition

23. Digestion of precipitates
Promoted Ostwald ripening
Larger crystals
Impurities reduced

25. Washing of precipitate
• Remove ions adsorbed
• Peptisation
• coagulation

26. filteration
•Ashless filter paper
•crucible

29. • A rubber policeman is a hand-held flexible
natural-rubber scraper attached to a glass rod
• To transfer residues of precipitate or solid on
glass surfaces when performing gravimtric
analysis.

31. Drying and ignition
• Remove moisture
• Precipitate to stable form
• Ashless filter paper leaves as fumes

33. Weighing and calculation
• Precipitate cooled
• Weighed
• calculated

34. CALCULATIONS
• Gravimetric calculations are based on the
fundamental stoichiometric calculations.

35. The gravimetric factor (GF) comes from a
combination of the mole ratios and the
formula weights used in the stoichiometric
calculation.

36. For example, if you were looking for SO3 and
your precipitate was BaSO4, the gravimetric
factor would be:
o The numbers, 80.064 and 233.391, are the formula
weights of SO3 andBaSO4, respectively

37. THANK YOU ALL….
Thank
you
all…..