Gravimetry

Introduction

Gravimetry is the quantitative measurement of an analyte by weighing a pure, solid form of the analyte. Obtaining pure solids from solutions containing an unknown amount of a metal ion is done by precipitation.

Since gravimetric analysis is an absolute measurement, it is a principal method for analyzing and preparing primary standards. A typical experimental procedure to determine an unknown concentration of an analyte in solution is as follows:

• quantitatively precipitate the analyte from solution
• collect the precipitate by filtering and wash it to remove impurities
• dry the solid in an oven to remove solvent
• weigh the solid on an analytical balance
• calculate the analyte concentration in the original solution based on the weight of the precipitate

Examples of Gravimetric Lab Procedures

Gravimetric Determination of Iron

1. Determine constant weight of the crucibles
2. Oxidation of iron sample
3. Precipitation of iron hydroxide
4. Ignition of iron hydroxide to iron oxide
5. Determine constant weight of the crucibles plus iron oxide
6. Calculation of iron in the sample