Qualitative Analysis
Introduction
Qualitative analysis is an important part of analytical chemistry. It is initially defined as analysis in which substances are identified or classified on the basis of their chemical or physical properties, such as chemical reactivity, solubility, etc. And it can tell you whether an atom, ion, functional group, or compound is present or absent in a sample, but it doesn't provide information about its quantity. Qualitative analysis is in high demand in different fields such as food science, pharmaceutical chemistry, petroleum industry, medical and criminology fields, etc. The methods employed in qualitative analysis vary in complexity, depending on the nature and complexity of the sample. Generally, we can divide qualitative analysis methods into conventional analysis methods and instrumental analysis methods. Conventional analysis methods rely on chemical reactions and can be performed in either "dry" or "wet" mode. In contrast, instrumental analysis methods rely on instruments, that is analytical measuring instruments with detectors as the main components.
Conventional Methods Used in Qualitative Analysis
Conventional qualitative analytical methods are typically used in inorganic chemistry and may involve the following:
- Color and color change test: Color may indicate the presence of certain elements in ionic form. For example, specific ions in solution have the specific colors: Cu2+ (blue), Cr3+ (green), CrO4- (yellow), MnO4- (purple), Ni2+ (green), Co2+ (pink or blue), Mn2+ (pink). In addition, when an indicator is added, the color change can indicate the acidity or alkalinity of the solution.
- Flame test: When a solid substance is subjected to a flame, it produces colors that are specific to certain elements. The flame colors of particular elements are as follows: sodium (intensive yellow), potassium (violet), calcium (brick-red), barium (green), bismuth (light blue), zinc (green). The color is an effect of the excitation of particular atoms which, while being restored to their original state, emits a light-quantum. Therefore, it is possible to determine whether a certain element is present in the sample.
- Precipitation test: This involves the use of reagents that react with the solution. By observing characteristics such as the shape, color and solubility of the precipitate, the composition of the substance can be determined. For example, the presence of iron ions can be determined by the reaction of iron ions with sulfide fish proteins to produce black iron sulfide precipitates. If the addition of silver ions to a solution containing nitric acid produces a white precipitate, it indicates that the solution may contain chloride ions.
- Gas production test: By observing the production of bubbles in the chemical reaction, the color and odor of the gas, and the interaction between the escaped gas and certain reagents, the composition and properties of the substance can be judged. For example, by reacting dilute hydrochloric acid with sodium carbonate to produce carbon dioxide gas, it is possible to determine the presence of carbonate ions.
Instrumental Methods Used in Qualitative Analysis
Advanced qualitative chemical analytical methods are typically used in organic chemistry and biochemistry and may involve the following (to name a few):
- Nuclear magnetic resonance (NMR) spectroscopy: It provides images of magnetic nuclei (13C, 1H), which can provide how the atoms within a molecule are arranged.
- Infrared (IR) spectroscopy: It uses a narrow range of electromagnetic radiation to show the type of vibration present in the test molecule, which can provide specific information about the functional groups of the molecule.
- Mass spectrometry (MS): This involves ionizing molecules and detecting the number of ions by determining the mass-charge ratio. This allows us to know both molecular mass of a material and information relating to how atoms are joined together.
- X-ray crystallography: This method is used to analyze the composition and structure of inorganic, organic, and biochemical compounds like medicines. It involves examining how x-rays diffract as they pass through the crystalline structure of crystallized substances. The double helix structure was discovered with the help of this method.
Alfa Chemistry is a global leading supplier of analytical chemistry reagents. We provide a wide range of analytical chemicals and instruments for qualitative analysis such as titration reagents (3S reagents for volumetric titration, indicators, karl fischer reagents and standards), instrumental analytical reagents (mass spectrometry reagents, spectroscopy reagents, etc.) and benchtop pH/ISE/EC/DO meters, portable pH/ISE/EC/DO meters, titrators and many others. If you cannot find the suitable products, Alfa Chemistry also offers you with custom synthesis service. If necessary, please don't hesitate to contact us.
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