4.16 : Volatilization

Volatilization gravimetry is an analytical technique that measures the mass lost due to the volatilization of the substance. This technique is used to estimate the amount of volatile material in a sample. To perform this method, heat a known amount of the sample to a high temperature in a crucible or other suitable vessel. The volatile substance in the sample evaporates, and the vapor is completely expelled from the crucible either by heating the sample or bubbling a stream of inert gas through the vessel. The remaining non-volatile components are left in the crucible, and their mass is measured on a scale. The difference in mass before and after volatilization gives the mass of the volatile substance, which can then be used to calculate its concentration in the original sample. This approach helps determine the water of crystallization present in hydrated compounds.

Alternatively, the sample can be treated with a chemical reagent in a closed vessel to form a chemically different volatile species with a known composition. The volatilized substance is then selectively absorbed in a pre-weighed trap filled with a suitable absorbent. For example, the carbon dioxide released from carbonate-containing compounds can be selectively absorbed in soda-lime, and NaOH can be selectively absorbed in a trap with non-fibrous silicate. The traps can then be weighed to determine the amount of absorbed material.