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Qualitative analysis involves determining metals and non metals (or metallic and non-metallic elements) present in a given sample. It is a process used to determine what elements (or radicals) are present in the sample.Whereas quantitative analysis involves determining how much (quantity) of a substance is present in a sample, qualitative analysis involves identifying what (quality) substances are present in a sample. Qualitative analysis has numerous applications. The following are some applications (importance) of qualitative analysis in real life;-

(a) Detection of poisonous substances in the environment: Sometimes it may be necessary to find out the chemical composition of contaminants in the environment. This may require the application of qualitative analysis procedures to identify the chemical composition of a given contaminant. Qualitative analysis methods are highly employed by environmental scientists to detect and identify different contaminants in the environment.

(b) Determination of ions present in a chemical substance: This is achieved through dissolution of a substance in distilled water. Then the characteristics of the solution formed serve as a clue to establish the type of elements present in a tested sample. The mixture formed following dissolution of a solid sample may be a clear solution, an emulsion or a precipitate. The solution or emulsion is further analysed to detect the ions present in it. The precipitate is then separated from the filtrate and both are subjected to further tests to identify the kind of elements present.

(c) Determination of the type of gases produced in a chemical reaction: Many chemical reactions are accompanied with evolution of gases, as one of the products of the reaction. In some cases, the smell of the gas may not suffice to detect the gas, especially if the gas is colourless and odourless. In such cases, the gas is subjected to various qualitative analysis tests in order to establish its identify.

(d) Finding the nature and identity of chemical substances: The nature of a chemical substance such as its solubility in water, characteristic smell, flame colour, and the characteristics of its reaction products can be used to identify the chemical substance under test. In this way, the nature and identity of unknown substance can ultimately be known.

(e) Determination of soil pH: Soils of given pH give specific colours when their solutions are added to certain types of indicators. This procedure is purely qualitative because it involves observation of the change in colour of indicators to determine the pH of the soil. For further details on the measurement of soil pH.

(f) Determination of soil composition: Qualitative tests are performed to determine the type of minerals contained in a particular soil. Such tests include test for nitrate, sulphate, chloride and phosphate ions. Determination of soil composition gives soil scientists information necessary for conservation.

(g) Application in medical and criminology fields: Qualitative analysis techniques are applied in medical field, for example in carrying out various tests such as testing blood and urine samples, determining the level of blood sugar, pregnancy diagnose and blood grouping. Most of these analytical tests are done to diagnose a wide range of diseases and medical conditions. For example:

  • in detecting the causative agents for typhoid (salmonella typhi), the blood is left to clot, or it is centrifuged in order to separate blood corpuscles from plasma. The plasma is then subjected to various qualitative tests to detect the presence of salmonella typhi.
  • in pregnancy diagnosis, a certain chemical is added to urine, where a specific change in colour of the urine confirms whether one is pregnant or not.

Qualitative analysis is also applied in blood grouping, whereby antibodies are added to the blood to determine the blood group. Agglutination of the blood corpuscles when antibodies are added help detect the group of the blood. Forensic scientists may use qualitative chemical analysis to identify substances left at crime scenes, which can be vital in convicting criminals. (h) Application in industries: Many industries use qualitative analysis in their efforts to perform better and make quality products.In chemical industries, the products often get contaminated by unknown contaminants. Qualitative tests are done to detect the contaminants. This may be followed by quantitative analysis aiming at finding out the quantity (amount) of the contaminant present.

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