Gravimetric Analysis

Gravimetric analysis determines an analyte by converting it to a pure solid of known composition and measuring that solid's mass.

Definition

Gravimetric analysis is a classical quantitative method that determines analyte amount from the mass of a pure, stoichiometrically defined solid produced from the analyte, typically by precipitation or by volatilization.

Scope

This topic covers precipitation gravimetry, in which the analyte is precipitated, filtered, washed, dried or ignited, and weighed, and volatilization gravimetry, in which mass change accompanies driving off a volatile component. It treats precipitate formation and purity, coprecipitation and digestion, the requirements for a good gravimetric form, and the stoichiometric conversion of weighed mass into analyte amount.

Core questions

• What properties make a precipitate suitable for accurate gravimetric determination?
• How do coprecipitation and digestion affect precipitate purity and particle size?
• How is the weighed mass converted to analyte amount through the gravimetric factor?
• When is volatilization gravimetry preferable to precipitation?

Key theories

Quantitative precipitation and the gravimetric factor

The analyte is converted essentially completely into a pure solid of known formula; the ratio of analyte mass to weighed-form mass, the gravimetric factor, follows from stoichiometry and turns the measured mass directly into analyte amount without external calibration.

Mechanisms

A reagent precipitates the analyte as a sparingly soluble solid; controlled conditions promote large, pure crystals and digestion reduces impurities trapped by coprecipitation. The precipitate is filtered, washed to remove adsorbed species, then dried or ignited to a stable weighing form of definite composition and weighed on an analytical balance. The gravimetric factor converts this mass to the analyte's mass. In volatilization gravimetry, the change in mass on heating measures a volatile constituent.

Clinical relevance

Gravimetry provides accurate reference determinations of constituents such as sulfate, silica, and certain metals, supports the certification of reference materials, and remains a standard method in mineral, cement, and water analysis where high accuracy matters more than speed.

History

Gravimetric determination was central to the rise of quantitative chemistry, with Berzelius achieving remarkably accurate atomic-mass measurements through careful precipitation and weighing. Fresenius systematized gravimetric procedures in the 19th century, and the physical understanding of precipitate formation advanced with Ostwald and later workers on nucleation and crystal growth.

Key figures

• Jöns Jacob Berzelius
• Carl Remigius Fresenius
• Wilhelm Ostwald

Seminal works

• harris2020
• skoog2014fac
• vogel2000

Frequently asked questions

What makes a good gravimetric precipitate?

It should be highly insoluble so precipitation is complete, easily filtered, readily purified of contaminants, and convertible to a stable solid of exactly known composition that can be weighed accurately.

What is coprecipitation?

It is the carrying down of normally soluble impurities along with the precipitate, by adsorption, occlusion, or inclusion; it degrades accuracy and is minimized by controlled precipitation conditions, digestion, and washing.