9.5 : Qualitative Analysis

Qualitative analysis is the process of identifying elements, ions, or compounds in an unknown sample. It is the first and most fundamental type of analysis based on the hierarchy of analytical goals. This hierarchy is significant as it provides a structured approach to scientific research, with qualitative analysis serving as the initial step, providing essential information before moving on to quantitative or other forms of analysis.

There are two main approaches to qualitative analysis: classical and instrumental methods. Classical methods rely on observable outcomes of specific chemical reactions, which can be identified through human senses (i.e., sight or smell). These reactions are either selective, meaning they favor the target analyte over other components, or specific, indicating they only react with the analyte. Preconditioning steps like precipitation or extraction may be used to improve the selectivity of these reactions. For instance, in a precipitation reaction, a specific reagent is added to the sample to form a precipitate, which can then be filtered and further analyzed.

Instrumental methods measure the analyte's unique physical properties. For example, in infrared (IR) spectroscopy, distinct peaks within a spectrum correspond to specific functional groups, allowing for accurate identification of compounds in the sample.

Both classical and instrumental methods form the basis of qualitative analysis, offering essential tools for identifying unknown components in various scientific samples.