Sulfate ions are medium s alts of sulfuric acid. Many of these compounds are highly soluble in water. Under normal conditions, substances are in a solid state of aggregation, have a light color. Many sulfate ions are of sedimentary origin, they are marine and lacustrine chemical sediments.
Building features
The crystal structure allows the content of complex anions SO42-. Divalent metal sulfates can be distinguished as common compounds. For example, sulfate ions, combining with calcium, barium, strontium cations, form insoluble s alts. These sediments are minerals that exist freely in nature.
Being in the water
In addition, the sulfate ion is formed during the dissociation of s alts, so these ions are found in surface waters. The main source of such compounds are the processes of chemical oxidation of sulfides and sulfur.
In significant quantities, sulfate ions enter water bodies during the death of living organisms, the oxidation of terrestrial and aquatic plant creatures. In addition, they are found in underground drains.
Ba significant amount of sulfate ion is formed in industrial and agricultural effluents.
Low mineralized water is characterized by the presence of SO42- ions. There are also stable forms of such compounds that have a positive effect on the mineralization of drinking water. For example, magnesium sulfate is an insoluble compound that accumulates in water.
Importance in the sulfur cycle
If we analyze the sulfate ion in water, it is necessary to note its importance for the full cycle of sulfur and its compounds in nature. Due to the action of sulfate-reducing bacteria, without access to atmospheric oxygen, it is reduced to hydrogen sulfide and sulfides. Due to the presence of oxygen in soil waters, these substances are re-converted to sulfates.
Under the action of sulfate-reducing bacteria and in the absence of oxygen, they are reduced to sulfides and hydrogen sulfide. But as soon as oxygen appears in natural water, they are again oxidized to sulfates.
In rainwater, the concentration of SO42- ions reaches 10 mg per cubic decimeter. For fresh waters, this figure is about 50 mg per dm3. In underground sources, the quantitative content of sulfates is significantly higher.
Surface waters are characterized by the relationship between the season and the percentage of sulfuric acid ions. In addition, the quantitative indicator is affected by human economic activity, reduction and oxidation processes occurring in wildlife.
Impact on water quality
Sulfates have a significant impact on the quality of drinking water. Their increased concentration adversely affects the organoleptic characteristics. Water acquires a s alty taste, its turbidity increases. The increased content of such anions adversely affects the physiological processes occurring in the human body. They are poorly absorbed into the blood from the intestines. At elevated concentrations, they give a laxative effect, disrupt the digestive processes.
It was possible to establish the negative effect of sulfates on the hair, the irritating effect on the mucous membrane of the eyes and skin. Due to the danger they pose to the human body, it is important to determine sulfate ions and take timely measures to reduce their amount in drinking water. According to the regulations, they should not exceed 500 mg per cubic decimeter.
Features of determination of anions in water
Laboratory studies are based on a qualitative reaction to sulfate ion with Trilon B. Titration is carried out in accordance with GOST 31940-12, established for SO42-. To conduct laboratory experiments related to the detection of the content of sulfate anions in drinking and waste water, barium chloride solutions are prepared with a given concentration (0.025 mol per dm3). In addition, solutions are required for analysis: magnesium s alts, ammonia buffer, Trilon B, silver nitrate, black eriochrome T indicator.
Algorithmanalysis steps
The laboratory assistant uses a conical flask, the capacity of which is about 250 ml. 10 ml of a magnesium s alt solution is added to it using a pipette. Next, 90 ml of distilled water, 5 ml of a buffered ammonia solution, a few drops of an indicator are added to the analyzed flask, titration is carried out with a solution of disodium s alt of EDTA. The process is carried out until the color changes to blue from red-violet.
Next, the amount of EDTA disodium s alt solution required for titration is determined. To obtain a reliable result, it is advisable to repeat the procedure 3-4 times. Using the correction factor, carry out a quantitative calculation of the content of sulfate anions.
Features of preparing analyzed samples for titration
Simultaneous analysis of two samples with a volume of 100 ml is carried out. It is necessary to take conical flasks designed for 250 ml. The laboratory assistant introduces 100 ml of the analyzed sample into each of them. Next, they add 2-3 drops of concentrated hydrochloric acid, 25 ml of barium chloride, put the flasks in a water bath. Heating is carried out for 10 minutes, then it is necessary to leave the analyzed samples for 60 minutes.
Then the samples are filtered so that there is no barium sulfate precipitate on the filter. The filter is washed with distilled water, the absence of chloride ions in the solution is checked. To do this, periodically conduct a qualitativereaction with silver nitrate solution. If cloudiness appears, this indicates the presence of chlorides in the solution.
Then place the filter in the flasks where the precipitation was carried out. After adding 5 ml of ammonia, stir the contents of the flask with a glass rod, unfold the filter, spread it along the bottom. Based on 5 mg of analyzed ions, 6 ml of EDTA disodium s alt are added to water. The contents are heated in a water bath, then boiled on an electric stove until the precipitate that has entered the water along with the filter is completely dissolved.
The duration of heating should not exceed five minutes. To improve the quality of the analysis, it is necessary to periodically stir the contents of the flask with a glass rod.
After the sample has cooled, add 50 ml of distilled water, 5 ml of a buffered ammonia solution, and a few drops of an alcohol solution of the indicator to it. Next, titration is carried out with an excess of disodium s alt EDTA of a solution of sulfate or magnesium chloride until a stable purple hue appears.
Conclusion
Sodium, potassium, sulfate ions are formed in wastewater not only due to various natural processes, but also as a result of human activities. In order for the water used for food not to have a negative impact on living organisms, it is necessary to monitor the quantitative content of various anions and cations in it.
For example, when carrying out titration of samples with Trilon B, it is possible to carry out quantitative calculations of the content of sulfate anions in samples,take specific measures to reduce this indicator (if necessary). In modern analytical laboratories, heavy metal cations, anions of chlorine, phosphates, pathogenic microorganisms are also detected in drinking water samples, which, when the permissible concentrations are exceeded, have a negative effect on the physical and emotional he alth of a person.
Based on the results of such laboratory experiments and numerous studies, analytical chemists conclude that water is suitable for consumption or that it needs additional purification, the use of a special filtration system based on chemical water purification.
