Qualitative Analysis (Encyclopedia of Science)
Qualitative analysis is the process by which a chemist determines what chemical elements are present in a given sample of material. For instance, many people are now concerned about the presence of lead in our environment. Lead is a highly toxic element that can cause both mental and physical problems and, in high doses, even death. Suppose that a parent wants to know if the paint used on his or her house contains lead. That parent can take a sample of the paint to a chemist for qualitative analysis. That analysis will tell whether or not lead is present in the paint.
The science of qualitative analysis is based on the fact that every element and compound has distinctive properties such as melting point, boiling point, color, texture, density, and so on. Every element also reacts with other chemicals in very distinctive ways. For example, the lead used in house paints reacts with a compound known as hydrogen sulfide to form a distinctive black precipitate.
Identification of elements
In many instances, the question facing a chemist is similar to the lead problem described above: what element or elements are present in some unknown mixture. Chemists have developed a systematic method for answering that question. The method divides the most common chemical elements into about six groups. The elements are grouped in each case according to the way...
(The entire section is 633 words.)
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