This document provides an overview of gravimetric analysis. It describes gravimetric analysis as a quantitative method that involves separating a substance into an insoluble compound and weighing it to determine the amount of the original constituent. The key steps are precipitation, filtration, washing, drying, ignition, weighing, and calculation. Gravimetric analysis is accurate and precise but also time-consuming and requires careful technique.

1. GRAVIMETRIC ANALYSIS
G. Nikitha, M.Pharmacy
Assistant Professor
Department of Pharmaceutical Chemistry
Sree Dattha Institute of Pharmacy
Hyderabad

2. CONTENTS
 Introduction
 Advantages
 Disadvantages
 Experimental Technique of Gravimetric Analysis
 Reference

3. INTRODUCTION
 Similar to the volumetric method, gravimetric analysis is used in the
quantitative determination of substances.
 Gravimetric analysis involves the separation of the constituents to be estimated
in the form of an insoluble compound of known composition.
 The insoluble compound is washed to free it from all impurities dried and
weighed either as such or ignited to leave a residue of some other comound
which is then weighed.
 Now from its weight and known composition, the amount of the constituent in
the given sample is calculated.
 From this the purity of the original compound is found out.
 Depending upon the nature of the sample, the results are expressed as
percentage weight (w/w) or weight in volume (w/v)

4. ADVANTAGES
 Accurate and precise: Gravimetric analysis is potentially more accurate and
more precise than volumetric analysis.
 Possible sources of errors can be checked: Gravimetric analysis avoids
problems with temperature fluctuations, calibration errors, and other problems
associated with volumetric analysis.
 It is an ABSOLUTE method.
 Relatively inexpensive

5. DISADVANTAGES
 But there are potential problems with gravimetric analysis that must be avoided
to get good results.
 Proper lab technique is critical.
 Careful and time consuming.
 Scrupulously clean glassware.
 Very accurate weighing.
 Coprecipitation.

6. EXPERIMENTAL TECHNIQUE OF GRAVIMETRIC
ANALYSIS
The technique of gravimetric involves the following steps
1. Precipitation
2. Filtration
3. Washing
4. Drying
5.Ignition
6. Weighing
7. Calculation

7. PRECIPITATION
In the gravimetric analysis the anion or Cation to be determined from a solution of
the substance is in a form that is having a definite itself or which leaves a
residue of a definite composition on ignitation
NaCl+ AgNO3 AgCl + NaNO3
ppt

8. FILTRATION
 The separation of the precipitate from the solution by filtration is carried out
either filter paper, sintered crucible.
 Different grades of filter paper have to be used for different precipitates. Ash-
less filter papers are used routinely. The size of the filter is selected according to
the bulk of the precipitate. The filter paper must be selected in such a way that
the pores of filter paper must be smaller than the size of the particles of the
precipitate.
 The precipitate is separated by filtration either through Whatman’s filter papers
because they are having very small ash valves. The diameter of filter paper may
vary according to the bulkiness of precipitate. The bulky precipitate like
aluminum hydroxide needs a large filter paper than dense precipitate ie barium
sulphate. The Folded filter paper is kept in a funnel moistened with the water
and pressed to expel the air. Then precipitate is transferred in a usual way and is
separated.

9. WASHING AND DRYING
Washing:
The precipitate must be washed free of all soluble matter otherwise impurities will
remain sticking to the precipitate. An important consideration in this connection
is the choice of the washing liquid.
Drying:
After washing precipitates which are collected in filtering crucibles may be dried
directly in a drying oven at 110-120C. The adsorbed water or solvent can be
easily removed from the crystalline ppt by heating.
Precipitates which are collected on filter papers are dried by placing the funnel on a
metallic chimney kept on tripos stand.

10. IGNITION
The air dried precipitates are then made to ignite in crucibles of platinum, silica,
nickel, in a muffle furnace at a desired temperature. The temperature of ignition
and period of ignition have been found to depend upon the nature of the
precipitate. During ignition the filter paper is first of all carbonized and the
temperature is slowly raised. If there exists risk of reduction of the precipitate
by carbon a low temperature for incineration would be used. For Instance for
barium sulphate, after ignition of precipitate it gets cooled and a drop of
sulphuric acid is added. The residue is again ignited to a high temperature. This
is called ash treatment.

11. WEIGHING
The ignited samples in the crucible are cooled for a few minutes and then they are
kept in a desicator, so that the moisture in atmosphere does not get absorbed by
the residue. Then it is accurately weighed on balance.

12. CALCULATIONS
In gravimetric determinations the result is generally calculated in terms of
constituent in the sample. If the constituent is weighed in the form in which
percentage is estimated the result is calculated by applying the following
relation:
P= Percentage of the constituent required
w= weight of the constituent
W= weight of the sample taken

13. REFERENCE
 Pharmaceutical Chemistry -Inorganic Volume-1 by G. R. Chatwal.
 Essentials of Inorganic Chemistry by Katja A. Strohfeldt.
 Indian Pharmacopoeia.
 M.L Schroff, Inorganic Pharmaceutical Chemistry.
 P. GunduRao, Inorganic Pharmaceutical Chemistry, 3rd Edition
 A.I. Vogel, Text Book of Quantitative Inorganic analysis.
 Bentley and Driver's Textbook of Pharmaceutical Chemistry.

14. THANK YOU