This article incorporates, in modified form, material from Illustrated Guide to Home Chemistry Experiments: All Lab, No Lecture.
Qualitative analysis is a structured set of methods used to determine the identities (but not the amounts) of the components that make up a mixture. Qualitative inorganic analysis is used to establish the presence or absence of particular elements or inorganic ions or compounds in an unknown sample. For example, an environmental technician might test a water sample to determine if arsenic, barium, or mercury is present. Qualitative organic analysis is used to establish the presence or absence of particular organic compounds or functional groups in an unknown sample. For example, a medical technician might test a urine sample to determine if glucose is present.
In modern university and corporate laboratories, many qualitative analyses are done instrumentally, using methods such as infrared and mass spectroscopy, nuclear magnetic resonance, neutron activation analysis, x-ray diffraction, spectrophotometry, chromatography, electrophoresis, and others. Before such instruments were introduced, chemists did qualitative analyses using wet-chemistry procedures, reacting the unknown substance with various reagents and observing the results. Such wet-chemistry procedures remain important today, both for field tests or initial screening preliminary to instrumental analysis and as a learning tool.
In this chapter, we’ll use various wet-chemistry procedures to do qualitative analyses of inorganic and organic compounds.
Everyday Qualitative Analysis
- Police and drug-enforcement agents use qualitative analysis field tests to do “pass-fail” preliminary analyses of suspect materials.
- Employers use qualitative analysis to test employees and prospective hires for drug use.
- Sports teams and sanctioning committees use qualitative analysis to test players for steroid use.
- Airports and public buildings use instrumental qualitative analysis to “sniff” for explosives.
- Environmental scientists use qualitative analysis to test soil, water, and air samples for the presence of toxic chemicals.