# 8: Gravimetric Methods

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Gravimetry includes all analytical methods in which the analytical signal is a measurement of mass or a change in mass. When you step on a scale after exercising you are, in a sense, making a gravimetric determination of your mass. Mass is the most fundamental of all analytical measurements and gravimetry unquestionably is the oldest quantitative analytical technique. Vannoccio Biringuccio’s Pirotechnia, first published in 1540, is an early example of applying gravimetry—although not yet known by this name—to the analysis of metals and ores; the first chapter of Book Three, for example, is entitled “The Method of Assaying the Ores of all Metals in General and in Particular Those That Contain Silver and Gold.” Although gravimetry no longer is the most important analytical method, it continues to find use in specialized applications.

• 8.1: Overview of Gravimetric Methods
Before we consider specific gravimetric methods, let’s take a moment to develop a broad survey of gravimetry. Later, as you read through the descriptions of specific gravimetric methods, this survey will help you focus on their similarities instead of their differences. It is easier to understand a new analytical method when you can see its relationship to other similar methods.
• 8.2: Precipitation Gravimetry
In precipitation gravimetry an insoluble compound forms when we add a precipitating reagent, or precipitant, to a solution that contains our analyte. In most cases the precipitate is the product of a simple metathesis reaction between the analyte and the precipitant; however, any reaction that generates a precipitate potentially can serve as a gravimetric method.
• 8.3: Volatilization Gravimetry
A second approach to gravimetry is to thermally or chemically decompose the sample and measure the resulting change in its mass. Alternatively, we can trap and weigh a volatile decomposition product. Because the release of a volatile species is an essential part of these methods, we classify them collectively as volatilization gravimetric methods of analysis.
• 8.4: Particulate Gravimetry
Precipitation and volatilization gravimetric methods require that the analyte, or some other species in the sample, participates in a chemical reaction. In some situations, however, the analyte already is present in a particulate form that is easy to separate from its liquid, gas, or solid matrix. When such a separation is possible, we can determine the analyte’s mass without relying on a chemical reaction.
• 8.5: Problems
End-of-chapter problems to test your understanding of topics in this chapter.