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Session- 2018 - 19

Module- 1

Theory of Volumetric and

Gravimetric Analysis

Presented by:

Dr. Pankaj Kumar Rastogi

Assistant Professor

Objective

Gravimetric Analysis

What is gravimetric analysis?

Gravimetry is among the most

accurate analytical techniques (but it

is tedious!).

T. W. Richards used it to determine

atomic weights.

He received the Nobel Prize in

for his work.

Theodore W. Richards

The separated precipitate is dried or ignited, possibly to

another form, and is accurately weighed.

From the weight of the precipitate and a knowledge of its chemical composition, we can calculate the weight of analyte in the desired form.

Types of Gravimetric Analysis

Gravimetric

analysis

Precipitation

method

Volatilization

method

Volatilization method

• In this method the analyte or its decomposition products are volatilised (dried) and then collected and weighed.
• or alternatively, the mass of the volatilise product is determined indirectly by the loss of mass of the sample.

Example for Precipitation

• Calcium can be determined gravimetrically by precipitation of calcium oxalate and ignition of the oxalate ion to calcium oxide.
• (^) Ca2+ + C 2 O 4 2 - → CaC 2 O 4 CaC 2 O 4 → CaO + CO 2 + CO
• The precipitate thus obtained are weighed and

Example for Volatilisation

• The analyte or its decomposition products are volatilised at a

suitable temperature.

• The volatile product is then collected and weighed, i.e. the mass of the product is indirectly determined from the loss in mass of the sample.
• Example, Water can be separated from most inorganic

compounds by ignition.

Advantages of Gravimetric Analysis

• Accurate and precise: Gravimetric analysis is

potentially

more accurate and more precise than volumetric analysis.

• (^) Gravimetric analysis avoids problems with

temperature

fluctuations, calibration errors, and other problems associated with

volumetric analysis.

• It is an ABSOLUTE method. i.e. it involves direct measurements without ant form of calibration.

• Relatively inexpensive

Steps in a gravimetric analysis

Preparation of the solution Precipitation Digestion Filtration Washing Drying or ignition Weighing Calculation

1.Preparation of analyte solution

• Gravimetric analysis usually involves precipitation of analyte from solution. To prepare the analyte solution, which may need:

1. – Preliminary separation to separate potential interferences before precipitating analyte