Precipitation Gravimetry: Avoiding Impurities

What is a common source of impurities in precipitation gravimetry?

What is the primary requirement for the precipitate in a precipitation gravimetric analysis?

What is the minimum percentage of the analyte that should be accounted for by the isolated precipitate to ensure accuracy?

What happens to the amount of analyte that precipitates when an inclusion is formed?

What type of reaction is typically used to generate a precipitate in precipitation gravimetry?

Why is an inclusion difficult to remove from the precipitate?

What is the main advantage of precipitation gravimetry methods developed in the nineteenth century?

How can an inclusion be removed from the precipitate?

What is the goal of extending the requirement for the isolated precipitate to account for at least 99.99% of the analyte?

What is the purpose of reprecipitation in removing an inclusion?

Gravimetric Methods of Analysis

Types of gravimetric methods include volatilization gravimetry, precipitation gravimetry, electrogravimetry, and particulate gravimetry.

Precipitation Gravimetry

Precipitation gravimetry involves the formation of an insoluble compound through the addition of a precipitating reagent to a solution of the analyte.
Most precipitation gravimetric methods were developed in the 19th century for analyzing ores and remain standard methods of analysis.
A precipitation gravimetric analysis requires a precipitate with low solubility, high purity, and known composition.

Theory and Practice

The precipitate must be easily separable from the reaction mixture.
Solubility considerations indicate that the precipitate's solubility must be minimal to achieve an accuracy of ±0.1%.

Solubility Considerations

To achieve an accuracy of ±0.1%, the isolated precipitate must account for at least 99.9% of the analyte.
Extending this requirement to 99.99% ensures that accuracy is not limited by the precipitate's solubility.

Avoiding Impurities

The precipitate must be free from impurities, which can arise from chemical and physical interactions at the precipitate's surface.
Impurities can be removed through reprecipitation, involving the dissolution of the initial precipitate and its reformation.

Impurities and Inclusions

Inclusions occur when interfering ions with similar size and charge substitute into the lattice structure.
The probability of forming an inclusion increases when the concentration of the interfering ion is greater than the lattice ion's concentration.
Inclusions are difficult to remove, but can be removed through reprecipitation.

Learn about the importance of removing impurities in precipitation gravimetry, including the sources of impurities and how to avoid them. Understand the chemical and physical interactions that affect the precipitate's surface.