This branch of science as analytical chemistry, studying the composition and structure of chemical compounds.It is used for the investigation of the unknown compound, or mixtures thereof.Qualitative analysis to determine the presence or absence of elements or radicals in the chemical compound, and the quantitative analysis includes the determination of chemical substances in the sample, i.e., the number of components constituting the mixture.For qualitative analysis is used for certain elements characteristic chemical reactions that are easy to perform.Qualitative reactions possible to observe the expected effects or lack of them.
Analytical chemistry is developing new and improving existing methods of analysis and their practical application, as well as the study of the theoretical foundations of analytical processes.Specialists in this field possess chemical, physical and physical-chemical methods of analysis.At the heart of many of them are qualitative reactions, which are used for the detection of radicals and components, as well as compounds which are a part of the samples.To study the qualitative and quantitative composition used:
- elemental analysis (determined by elemental composition);
- molecular analysis (set structure of chemical compounds at the molecular level);
- structural analysis (a type of molecular analysis, explores the spatial structure of atoms and molecules, their molecular weight and empirical formula);
- functional analysis (organic compounds studied by functional groups).
thus can be recognized, both inorganic and organic compounds.In the presence of specific elements can appear or disappear paint, stand, or to dissolve the precipitate, effervescence observed and so on.If the quality of the reaction are chosen correctly, i.e. selective (selective) for a particular cation or anion, as well as highly sensitive (i.e., threshold detection allows the small amount), the result is a valid result - the conclusion of the presence or absence in a sample cell or substance.The basis of this analysis of aqueous solutions are known ion qualitative reactions.
For inorganic compounds, they often occur in aqueous solutions, but in the case of alkali metal cations detection is performed when making dry salts in the middle (the hottest) of the flame of a spirit lamp.Lithium cation (Li +) will color the flame in a dark pink color.Potassium cations (K +) - a violet, sodium (Na +) - yellow, rubidium (Rb +) - red, cesium (Cs +) - in blue.Qualitative tests cations may be carried out for barium salts: the presence of barium cations (Ba2 +) is set by adding a reagent to sulfate ions (SO42-), since the resulting barium sulfate precipitated white color, which does not dissolve in acids: Ba2 + + SO42- →BaSO4 ↓.The presence of lead cation (Pb2 +) found when exposed to aqueous salt sulfide (S2-), as a result of lead sulfide is formed, which precipitates as a black precipitate: Pb2 + + S2- → PbS ↓.Such qualitative reactions known as cations and anions at very much, and they are described in analytical chemistry.
choosing qualitative reactions for the test sample, it is useful to know the general rules of the solubility of chemical compounds:
- All nitrates are soluble.
- Virtually all salts of potassium, sodium and ammonium salts are soluble.
- All chlorides, bromides and iodides are soluble, except for silver halide, mercury (I) and Pb (II).
- all soluble sulfates, except barium sulfate, strontium and lead (II), which are insoluble, and sulphates of calcium and silver, which are moderately soluble.All
- carbonates, sulfites and phosphates are insoluble except carbonates, sulfites and phosphates of potassium, sodium and ammonium.
- All insoluble sulfides except sulfides of alkali metals, alkaline earth metals and ammonium.
- All hydroxides are insoluble except alkali metal hydroxides.Hydroxides of strontium, calcium and barium are sparingly soluble.
Such organic substances such as alkane (saturated hydrocarbons) or alkenes (unsaturated hydrocarbons) can be detected using a solution of potassium permanganate, which in the first case will not change their color as paraffinic hydrocarbons with permanganate not react in the cold.In the second case, the solution becomes colorless due to reaction Wagner (e.g. ethylene): 2KMnO4 + 3C2H4 + 4H2O - → 2KOH + 3CH2OH-CH2OH + 2MnO2 ↓.The resulting precipitate of manganese dioxide having a brown color.Proteins are complex organic compounds, which provide vital activity of any living organism.Their huge set, the determination of their of great practical importance.For these purposes the qualitative reactions to proteins, they are divided into color and name.With their help, they are not determined by the proteins themselves, and amino acids, their constituent.
