4-2 ions in natural waters by titration of lead salts in the presence of dithizone

I.2. Qualitative composition of substances. Qualitative and quantitative analysis
The main task of qualitative analysis of inorganic substances is to determine the chemical composition of the test substance and its cations and anions. When a qualitative analysis is performed chemically, the identified component (atom, ion, molecule) is converted into the following compound: the various components of the solution are determined by various chemical reactions (precipitation, color formation, gas release, etc.). If we add an excess of NH4OH solution to the saline solution of Cu (II) ion, the resulting solution turns blue, forming a complex salt.
Cu⁺² + NH₄OH = │Cu(NH₃)₄│ + H₂O (blue)
It can be concluded that the cation Cu ² can be detected using a solution of NH4OH, or Cu ² can be formed using the CNS anion to form a blue complex (if the solution does not contain Fe ³ ions), a reaction specific to Cu ² ions. Chemical reactions are basically in two different directions

• 
  wet
  
• 
  carried out in a dry manner.
  

In the dry method, the test substance and reagents are obtained in a solid state and the reaction is carried out by friction (or at high temperatures) of the reagents. In the second method, the interaction of the reagents with the test substance is observed in solution. Dry reactions include, for example, reactions involving the flame dyeing of metal salts, which are also used. In the seventeenth century, R. Boyle discovered the "wet" method of reactions and introduced analytical chemistry as a separate science. In practice, qualitative analysis is mainly carried out in a "wet" way. In this case, the sample under analysis is first dissolved in solvents and then tested. Distilled water, mineral acid solutions: HCL, HNO3, H2SO4, alkalis, alcohols are used as solvents. A substance dissolved in an acid undergoes a chemical conversion into a water-soluble compound, a salt.
CuO + H₂SO₄ = CuSO₄ + H₂O;
Fe(OH)₃ + 3HCl = FeCl₃ + 3H₂O;
CaCO₃ + 2HNO₃ = Ca(NO₃)₂ + H₂O + CO₂Î
CuSO₄, FeCl₃, Ca(NO₃)₂, - Cu⁺², Ca⁺² cations can be detected in solutions with a specific reagent. Methods of analytical reactions Depending on the amount of substance that analytical reactions determine the solution, qualitative analysis is divided into macro, semi-macro, micro, ultramicro, submicro, subultromicro methods. Micro, semi-macro and microanalysis methods are mainly used in the study of analytical chemistry. When performing the reaction by microanalysis, the dry weight of the test substance should be from 0.5 g to 1 g or the volume of the solution should be from 5 ml to 10 ml. When performing the microanalysis, the weight of the test substance should be approximately 100 times less than in the microanalysis. At the time of semi-microanalysis, the dry mass of the substance should be in the range of 0.05-0.1 g or 0.5-1 ml in solution, so that its weight and volume are 1/10 (sometimes 1/20) of the microanalysis. Depending on the weight or volume of the test substance, the reactions are performed in a test tube, droplet or microcrystalloscopic method.
Test tube method. During the analysis, the reactions are carried out in glass tubes with a volume of 2-5 ml.
Drop analysis. This method is developed by N.A. Tanaev, using glass or porcelain plates under analysis, or one drop of the test solution and one drop of reagent should be placed on the surface of the filter paper. The reaction should result in the formation of a precipitate or the formation of a color on the glass plate. An example is the reaction of Chugaev in the determination of the third group of cations Ni + 2. It is possible to determine the desired ion in the presence of several ions by droplet reactions.
Drop analysis. This method is developed by N.A. Tanaev, using glass or porcelain plates under analysis, or one drop of the test solution and one drop of reagent should be placed on the surface of the filter paper. An example is the Chugaev reaction in the determination of the third group of cations Ni + 2.
2Ba⁺² + Cr₂O₇^- + H₂O = 2BaCrO₄ + 2H⁺ Ba⁺²
Only potassium dichromate is used to separate the Ba⁺² cation in solution, and the reagent is added until the cation is completely precipitated. The task of quantitative analysis is to determine the amount of individual elements or compounds that make up a substance. The data obtained from the test are expressed as a percentage. Quantitative chemical analyzes include gravimetric analysis, volumetric (titrimetric) analysis, and gas-gasometric analysis. Quantitative analysis uses ionic reactions in qualitative analysis. For example, if it is necessary to determine the amount of chlorine, or chloride - ion, it is precipitated in solution with a silver ion.
NaCl + AgNO₃ = AgCl + NaNO₃
Cl^- + Ag⁺ = AgCl
Based on this reaction, the amount of chlorine can be determined in various ways.
There are 2 different types of gravimetric analysis:

• 
  dipping;
  
• 
  driving method.
  

If we determine the amount of substance by gravity analysis, this method has long been known and gives sufficiently accurate results, but it takes a long time to perform. The analysis is performed in the following order: the sample of the test substance is weighed on an analytical balance, then the sample is transferred to solution, the required component (element to be quantified, ion) is precipitated as a low-solubility and clear compound, the precipitate is filtered, separated from the solution, centrifuged. The precipitate is heated to a constant temperature and weighed on an analytical balance. Knowing the mass of the sediment, the percentage of the required component is calculated. AgNO₃
If it is necessary to determine the amount of chlorine, then the chlorine ion is precipitated in solution using AgNO₃. Based on this reaction, chlorine can be determined by another method - titration, which is used to precipitate Cl- ions Reagent) - can also be determined by measuring the volume of AgNO3 solution - volumetric method. The advantage of the method of volumetric analysis is that it takes less time (15-20 minutes, 5-6 hours for gravimetric analysis) to perform this analysis.
Gas analysis. The method of gas analysis is widely used in the control of technological processes. The essence of this method is that when a mixture of gases is passed through a special reactive solution, the volume of the gas mixture is reduced due to the absorption of certain components into the solution. Based on this, the percentage of some gases in the mixture is determined. For example, the amount of carbon dioxide in a gas mixture is determined by mixing a certain amount of gas mixture with a solution of caustic soda and shaking it so that the alkaline solution completely absorbs the CO2 gas. The amount of gas absorbed is found by decreasing the volume of the gas mixture. The reaction proceeds according to the following equation.
2KOH + CO₂ = K₂CO₃ + H₂O
However, chemical methods do not always meet the requirements of control. Due to the low sensitivity and selectivity of chemical methods, it is impossible to identify very small amounts of elements in various substances. while turbid substances cannot be used under existing solution conditions, so much attention is now being paid to creating methods that are very sensitive and have a short analysis period. In this regard, physical and physicochemical methods are very effective.
I.3.Pollution of water basins
In 1995, the Hydro-Information Center conducted monitoring and observations on the level of groundwater pollution and re-evaluated the forecast resources and reserves of such waters from all sources. The largest decrease in fresh groundwater reserves with a mineralization of up to 1 g / l occurred in Bukhara and Navoi regions of the country. They are almost completely deprived of fresh groundwater sources. Below Kattakurgan and in the Surkhandarya valley, fresh groundwater reserves are declining. In the eastern sector of the Sokh freshwater source, water hardness has appeared, and in the hilly region - Altiyarik - Besholish, groundwater is contaminated with oil products. Chirchik, Ahangaron rivers, valleys, in the upper and middle parts of the Zarafshan river valley, in the Fergana valley of the Syrdarya river valley are polluted under the influence of industrial enterprises (Chirchik, Tashkent, Yangiyo 'l, Angren, Almalyk, as well as agro-industrial, communal and other facilities).
In Tashkent region, in the middle part of the Chirchik groundwater source, in the middle part of the Chirchik groundwater source, in the underground stream below the city of Chirchik, previously wide islands of groundwater pollution 3-8 STCHK (mine road) 'maximum allowable concentration), 1-2 STCHK for caprolactam and 14-70 STCHK for nitrates. In 1994, the length of the island of nitrogen pollution was 2.5-7.5 km, which stretched in the direction of the Kibray drinking water intake facilities. In general, as a result of the reduction of industrial effluents from Elektrokimyosanoat, UzMIC (Combustion and Refractory Metals Combine), since 1994 there has been a tendency to reduce the area of ​​nitrate contamination to the local level of 0.5 STCHK.

In 2002-2004, the Chirchik groundwater source was polluted with petroleum products, ranging from 0.4 to 0.6 million cubic meters. The level of pollution at local sites varies from 2.0 to 10.0 STCHK (Kuylik, Pakhta oil depots, railways, some oil depots, car washes, AYOQS, Salar aeration station, Tashkent residential areas - Sergeli, ring It is known that the amount of petroleum products in groundwater at the boundaries of the road) exceeds the STCHK. In some sections of the Kok-Aral groundwater sources, groundwater pollution was found to be 6 STCHK for selenium, 2 STCHK for cadmium, and 2-3 STCHK for strontium and manganese. It should be noted that the Ahangaron groundwater is a specific factor in the formation of regional and local pollution and is mainly used only for irrigation. In Isfara and Sokh, the mineralization rate increases from 1.5 g / l to 2.3 g / l. In other groundwater sources of the Fergana Valley, as well as in connection with agricultural activities, there is an increase in mineralization from 1.4 to 1.7 g / l and hardness to 17.2 mg-eq / l. In the Republic of Uzbekistan in 2002-2004, the protected areas of drinking water quality that do not meet the standards for chemical indicators in municipal water pipelines In 2002-2004, the State Committee for Nature Protection of the Republic of Uzbekistan Large-scale efforts have been made by the Committee to grant the status of protected natural areas (MTHs) to areas of fresh groundwater of national and regional importance, and to define coastal areas in the region for the protection of rivers. Granting the status of protected natural areas to a total of 19 large areas of fresh groundwater of national and regional importance, water protection zones and banks of rivers such as Kashkadarya, Zarafshan, Chirchik, Surkhandarya, Naryn and Karadarya. The work on the designation of yi areas is almost complete. The total area of ​​water protection zones of these rivers is 73116.2 hectares, including 9852.1 hectares of coastal areas. A project-search work has been launched to identify water protection zones and coastal areas of the Amudarya and Syrdarya rivers (flowing through the territory of Uzbekistan). Inventory of the condition was carried out. As a result, 214 unattended wells (not on the balance sheet of any organization) were identified. In cooperation with the State Committee for Geology and Mineral Resources, 64.0 million soums were allocated for their liquidation and installation of tap control devices. was carried out. 18.7 million soums from the nature protection funds were used to complete the work. As a result of these works, potentially environmentally hazardous sources of fresh groundwater pollution have been identified. The State Committee for Nature Protection, together with experts from the Ministry of Agriculture and Water Resources and the State Committee for Geology and Mineral Resources, has developed measures to ensure environmental safety in areas of fresh groundwater formation. the executive is overseeing the ustio. To date, 17 objects have been removed from the water protection zone out of 18 potentially dangerous objects located in the water protection zone of the Kashkadarya River.
There are 21 potentially environmentally hazardous objects on the Chirchik River in the Tashkent water protection zone on the border of the Tashkent region. 2 possible objects were removed, water supply of 1 object was transferred to circulating water supply. 14 ecologically dangerous objects were removed from the water protection zone of the Surkhandarya River. 12 potentially ecologically dangerous objects have been identified in the Karadarya River in the Andijan region. Measures are being taken to prevent the pollution of the river and to remove these facilities from the water protection zone. A plan of preventive measures to prevent water pollution and ecologically improve the Kara-Darya basin in Namangan region has been developed and approved. In Namangan region, the authorities have developed and approved measures to remove potentially environmentally hazardous facilities from the Naryn River protection zone. As a result of these measures, 5 of the 5 environmentally hazardous facilities located on the river water protection boundary, which should be removed from the area, were removed from the protection zone.