The document discusses gravimetric analysis, detailing its principles and essential steps including sampling, precipitation, digestion, filtration, washing, drying, weighing, and calculation. It emphasizes the importance of ensuring the purity of precipitates by managing co-precipitation and post-precipitation. Additionally, the document provides a practical example of estimating barium sulfate and outlines the applications of gravimetry in analyzing standard solutions.

1. Gravimetric Analysis
Santosh Kumar
Assistant Professor
Department of Pharmacy
Sarala Birla University, Ranchi
Email: santosh.kr@sbu.ac.in

2. Chapter 3, Unit 3 - Pharmaceutical Analysis (P.A.)
Syllabus
• Understanding the principles and steps in gravimetric analysis.
• Ensuring the purity of precipitates: managing co-precipitation and
post-precipitation.
• Estimation of barium sulfate as an example.

3. Gravimetry
• Gravimetry is a method used to measure the weight or amount of a
substance by converting it into a solid form (precipitate) through a
chemical reaction.
• The process determines the amount of the substance in its pure form as
a solid precipitate.
• Breakdown of Terms
• Gravi means mass, and metry means measurement.
• Together, gravimetry means measuring the mass of the precipitate to
determine the amount of substance.

4. Gravimetry

5. Gravimetry
Principle of Gravimetry
• Gravimetric analysis is based on converting ions or elements into a
pure, solid form through a precipitation reaction. This solid, or
precipitate, can then be easily weighed and measured to determine
the amount of the substance.

6. Steps Involved in Gravimetric Analysis
1.Sampling - Preparation of solution
2.Precipitation - Formation of solid precipitate
3.Digestion (Ostwald Ripening) - Growth and settling of precipitate
4.Filtration - Separating precipitate
5.Washing - Removing impurities
6.Drying / Ignition - Removing moisture or stabilizing precipitate
7.Weighing - Measuring mass
8.Calculation - Determining amount of original substance

7. Sampling

8. Precipitation
• To prepare a precipitate, add a precipitating reagent to the solution.
• Definition: Precipitation is the process of forming a solid from a
solution when a chemical reaction occurs.
• Importance: Precipitation is necessary to convert substances into
their pure forms.
• Example of Reagent: Dilute sulfuric acid (H₂SO₄) can be used as a
precipitating reagent.

9. Digestion (Ostwald Ripening)
Definition: Digestion is a process where smaller particles of a
precipitate are converted into larger particles by allowing the
precipitate to stand in the presence of mother liquor.
Mother Liquor: This is the solution that contains the precipitate.
Procedure:
• The precipitate is allowed to stand for 12-24 hours at room temperature.
• To increase the rate of digestion, the temperature can be raised.

10. Digestion (Ostwald Ripening)

11. Filtration
• Definition: Filtration is the process of separating the precipitate from
the mother liquor using filter paper (e.g., Whatman filter paper).
• Process:
• The filter paper retains the solid, which is called the residue.
• The liquid that passes through the filter paper is collected below and is called
the filtrate.

12. Washing
• Definition: During the washing process, precipitate may be
contaminated with impurities.
• Purpose: It is necessary to wash the precipitate to remove these
impurities.
• Method:
• Wash the precipitate using warm water or a suitable solvent.

13. Drying
• Definition: Drying (or ignition) is used to remove the water from the
precipitate that remains after washing.
• Procedure:
• Drying can be done by heating the precipitate at 110°C to 120°C for 1 to 2
hours.
• Ignition: This can be performed at much higher temperatures if the precipitate
needs to be converted into a more suitable form for weighing.

14. Weighing
• Process: After drying, allow the residue (precipitate) to reach room
temperature.
• Measurement: Weigh the residue accurately using an analytical
balance.

15. calculation

16. Purity of Precipitate
• Definition: When a precipitate is separated from the solution, it is not
always pure; it may be contaminated with some amount of impurities.
• Factors Influencing Impurities: The amount of impurities depends
on the nature and condition of the precipitate.
Types of Impurities
• Co-precipitation
• This occurs when impurities are trapped within the precipitate during its formation.
• Post-precipitation
• This refers to the formation of additional precipitate after the initial precipitation, leading
to contamination.

17. Co-Precipitation
• Definition: Co-precipitation is a condition/process during the
formation of a precipitate in which the precipitate is contaminated by
substances that are soluble in the mother liquor.
• Types of Co-Precipitation:
• Surface Adsorption:
• In this process, impurities are adsorbed on the surface of the precipitate.
• Occlusion:
• In this process, impurities get trapped inside the precipitate during the growth of the
precipitate crystals.
• Example: AgI can adsorb on BaSO₄ precipitate in alkali nitrates.

18. Co-Precipitation

19. Post-Precipitation
• Definition: Post-precipitation is a condition/process that occurs after
the formation of a precipitate, where impurities get adsorbed on the
surface of the precipitate.
• Occurrence:
• This mainly occurs when the precipitate is allowed to stand in the presence of
the mother liquor after its formation.

20. Post-Precipitation

21. Estimation of barium sulphate

22. Procedure

23. calculation

24. Applications of Gravimetry
1. Analysis of Standard Solutions: Gravimetry is used in the analysis
of standard solutions to determine concentrations accurately.
2. Accuracy in Analysis:
1. While gravimetric methods can be time-consuming, they provide better
accuracy and reliable results compared to some other methods.
3. Determination of Various Ions:
1. Chloride as silver chloride (AgCl).
2. Lead as lead chromate (PbCrO )
₄ .