Qualitative chemical tests collect data on a sample’s observable but non-measurable properties. They can be used to test unknown chemical compounds, inspect products for quality control, and conduct research into the applications of different chemicals. In most cases, a lab setting is required to provide access to equipment as well as a clean working environment in which to record observations. Students in chemistry typically learn some qualitative techniques in addition to quantitative techniques, which involve measuring a property.
The goal of these tests is to gather data that can be used to rule out or confirm possibilities. If a sample’s identity is unknown, certain characteristics will quickly rule out possible candidates. It can assist with purity assessments and checks to ensure that a compound performs as intended and as advertised in the case of quality control. Technicians can perform quantitative testing to detect measurable properties while performing qualitative chemical tests.
An observation on the appearance of a sample is a simple example. Whether it’s a gas, liquid, or solid, the way it looks can reveal a lot about what it is. The color can be noted by the observer performing qualitative chemical tests, as well as whether the color changes in different environments or in response to specific chemical agents. Spectroscopy evaluations can add to the body of knowledge about what’s inside by providing more information about the sample’s performance.
Another aspect of qualitative chemical tests is solubility testing. Determining whether a compound is soluble, as well as the behavior of the compound when mixed with a solvent, can provide important information about what it contains. Melting and boiling points can also provide additional information, complementing the technician’s observations. These tests are more quantitative in nature because they produce absolute measurements, but they can be classified as qualitative when used to evaluate an unknown sample. Compounds that melt at lower temperatures, for example, are ruled out by a high melting point.
The technician takes careful notes on the equipment used and the behavior of the sample while performing these tests. If the technician’s work on qualitative chemical tests is called into question later, he or she will want to be able to point to the records to show that they were done correctly. Unknown samples, which may be toxic or dangerous, are also treated with caution by technicians, who must wear appropriate skin and face protection until the chemicals in the sample are identified.