Chemical analysis of water in a school laboratory. Studies of the mineral composition of water (carried out in a school laboratory). Natural sources of drinking water

Usually in hydrological laboratories to determine the quality of water, a standard sample is carried out - the determination of the biochemical oxygen demand (BOD). In this case, the determination of the content of oxygen dissolved in water is carried out either by the Winkler chemical method, or by the physicochemical method, based on an amperometric study.

If this work did not suit you at the bottom of the page there is a list of similar works. You can also use the search button

Introduction. ... ... ... ... ... ... ... ... ... 2

1. Literature review. ... ... ... ... ... ... ... 4

1.1. Oxygen in the environment. ... ... ... ... 4

1.1.1. Oxygen as a component of air. ... ... ... 4

1.1.2. Oxygen in water. ... ... ... ... ... ... ... 5

1.1.2.1. Content dependency

Oxygen in water from various factors. ... ... ... 5

1.1.2.2. Dissolved oxygen as

criterion for assessing water pollution. ... ... ... ... 7

1.2. Determination of oxygen dissolved in water. ... ... nine

1.2.1. Winkler's chemical method. ... ... ... ... ... nine

1.2.2. Physicochemical method. ... ... ... ... ... 21

2. Experimental part. ... ... ... ... ... ... 22

2.1. Preparation of solutions. ... ... ... ... ... ... 22

2.2. Working out the technique. ... ... ... ... ... ... ... 23

2.3. Water sampling and sample preparation. ... ... ... ... 26

2.4. Analysis of water for the content of dissolved oxygen. ... 26

3. Discussion of the results. ... ... ... ... ... ... 28

Conclusions. ... ... ... ... ... ... ... ... ... thirty

List of used literature. ... ... ... ... 31

Application. ... ... ... ... ... ... ... ... 32

Introduction.

Of the chemical elements found in large quantities on the planet, half are biogenic elements, one of which is oxygen. In the environment, molecular oxygen is contained in a gaseous state in air and is also dissolved in water.

Oxygen is a strong oxidizing agent and reacts with many reducing agents. Therefore, the presence of such substances in the environment reduces the concentration of oxygen available to living organisms. This property of oxygen is the basis for assessing water pollution by reducing agents, primarily organic substances.

Usually in hydrological laboratories to determine the quality of water, a standard sample is carried out - the determination of the biochemical oxygen demand (BOD). In this case, the determination of the content of oxygen dissolved in water is carried out either by the Winkler chemical method, or by the physicochemical method, based on an amperometric study.

Often, the study of hydrochemical indicators of water bodies is carried out within the framework of special laboratory workshops in universities, as well as during school environmental monitoring. The amperometric method is of little use under these conditions. Carrying out research by the Winkler method requires simple and affordable analytical techniques.

In this regard, the goal our work was to test the Winkler method in our laboratory conditions and prepare detailed recommendations for its use in school environmental monitoring and special laboratory workshops at our university.

Tasks:

1. Review the literature on methods for the determination of oxygen in water;
2. To work out the method of determination;
3. Prepare guidelines for conducting analyzes in a school environment.

1. LITERATURE REVIEW

1.1. Oxygen in the environment.

1.1.1. Oxygen as a component of air.

Oxygen is the most abundant element in the earth's crust. In the atmosphere it is about 23%, in the composition of water - about 89%, in the human body - about 65%, sand contains 53% oxygen, clay - 56%, etc. If you calculate its amount in the air (atmosphere) , water (hydrosphere) and part of the solid earth's crust (lithosphere) accessible to direct chemical investigation, it turns out that oxygen accounts for about 50% of their total mass. Free oxygen is contained almost exclusively in the atmosphere, and its amount is estimated at 1.2-10 15 tons. For all the enormity of this value, it does not exceed 0.0001 of the total oxygen content in the earth's crust.

Free oxygen is composed of diatomic molecules. Under normal pressure, it liquefies at -183 ° C and solidifies at -219 ° C. In the gaseous state, oxygen is colorless, and in the liquid and solid it has a pale blue color.

Many life processes are associated with molecular oxygen. This substance supports the respiration of most living creatures living on the planet. In this regard, it is vitally important to maintain the balance of molecular oxygen in water and air.

The binding of molecular oxygen occurs mainly through oxidation reactions. In this case, the conversion of molecular oxygen into the composition of other gases of the atmosphere, minerals, water, organic matter, etc. is carried out.

Along with providing vital processes, molecular oxygen plays an exceptional role in protecting living organisms from the harmful effects of short-wave ultraviolet radiation from the Sun.

Oxygen atoms can interact with O 2 with the formation of ozone:

O + O 2 = O 3

Ozone is an allotropic modification of oxygen and is a gaseous substance under normal conditions. The formation of ozone occurs intensively in the stratospheric layers of the atmosphere, where the so-called ozone layer is concentrated. The ozone layer absorbs UV radiation with a slightly longer wavelength than molecular oxygen - 220-320 nm. In this case, the process of dissociation of ozone into molecular and atomic oxygen occurs:

О 3 = О 2 + О

The products of this reaction can react with each other to produce the initial ozone. Thus, there is a balance between the processes of ozone formation and its destruction.

1.1.2. Oxygen in water

1.1.2.1. Oxygen solubility dependence

in water from some factors.

Despite the fact that most of the molecular oxygen is contained in atmospheric air, its amount in water is also quite large. Oxygen dissolved in water supports the vital activity of aquatic organisms and in many cases is a limiting factor for the spread of living organisms.

The solubility of this gas in water depends on many factors. So at elevated temperatures, the solubility of oxygen, like other gases, in water decreases. This distinguishes gases from most solids, the solubility of which increases with the temperature of the solvent. This unusual behavior of gases is quite natural, since an increase in the kinetic energy of particles during heating leads to the fact that gas molecules leave the solution more easily than return to it. Therefore, with prolonged boiling, the solution can be almost completely degassed - the dissolved gas can be removed from it.

The dependence of the solubility of substances on pressure is also traced. Pressure has little effect on the solubility of solids and liquids, but significantly affects the solubility of a gas. If, upon evaporation of a liquid, molecules with increased kinetic energy pass into vapor, then it is obvious that molecules with reduced kinetic energy must pass from a gas to a liquid solution.

At a given temperature, the number of such molecules is proportional to the gas pressure. Consequently, the amount of gas dissolved in a liquid must be proportional to its pressure, which is expressed by Henry's law: at a given temperature, the concentration of a dissolved gas is proportional to its partial pressure.

C i = K i + R i,

where C i - gas concentration in solution, P i - its partial pressure and Kі - Henry's constant, which depends on the nature of the gas and solvent. TOі is the equilibrium constant of the gas dissolution process.

Since at constant temperature To i is always the same, then the expression makes sense:

K = C і1 / P і1 = C і2 / P і2,

where С і1 and С і2 Is the concentration of the dissolved gas at partial pressures, respectively Рі1 and P і2.

The partial pressure of oxygen in the air will be equal to:

P O 2 = P atm. * 0.21,

where 0.21 is a coefficient indicating the amount of oxygen in the air; R atm. - Atmosphere pressure.

Then, in order to find out the concentration of dissolved oxygen in water at different pressures and constant temperatures, it is enough to know the solubility of oxygen in water at this temperature, at a pressure of 760 mm. rt. Art. and the atmospheric pressure at which the experiments were carried out.

1.1.2. Oxygen dissolved in water

as a criterion for assessing pollution.

Oxygen dissolved in water is one of the most important biohydrochemical indicators of the state of the environment. It ensures the existence of aquatic organisms and determines the intensity of oxidative processes in the seas and oceans. Despite the high flow rate, its content in the surface layer is almost always close to 100% saturation at a given temperature, salinity and pressure. This is due to the fact that its loss is constantly replenished both as a result of the photosynthetic activity of algae, mainly phytoplankton, and from the atmosphere. The latter process occurs due to the tendency of oxygen concentrations in the atmosphere and the surface layer of water to dynamic equilibrium, in violation of which oxygen is absorbed by the surface layer of the ocean.

In the zone of intensive photosynthesis (in the photic layer), a significant supersaturation of seawater with oxygen is often observed (sometimes up to 120-125% and higher). With increasing depth, its concentration decreases due to the weakening of photosynthesis and consumption for the oxidation of organic substances and respiration of aquatic organisms, and at some depths in the upper layer, its formation and consumption are approximately the same. Therefore, these depths are called compensation layers, which move vertically depending on the physicochemical, hydrobiological conditions and underwater illumination; for example, in winter they lie closer to the surface. In general, oxygen deficiency increases with depth. Dissolved oxygen penetrates into the deep layers exclusively due to vertical circulation and currents. In some cases, for example, when vertical circulation is disturbed or in the presence of a large amount of easily oxidizable organic matter, the concentration of dissolved oxygen can drop to zero. Under such conditions, reduction processes begin to take place with the formation of hydrogen sulfide, as, for example, occurs in the Black Sea at depths below 200 m.

In coastal waters, a significant oxygen deficiency is often associated with their pollution with organic substances (oil products, detergents, etc.), since these substances are reducing agents. The oxidation reaction triggered by this transfers oxygen from its molecular form to other compounds, rendering it useless for maintaining life.

Based on this, it is believed that the determination of the oxygen concentration in water is of great importance in the study of the hydrological and hydrochemical regimes of water bodies.

Usually, oxygen dissolved in water is determined by the Winkler volumetric method. Physicochemical methods are also used: electrochemical, gas chromatographic, mass spectrometric and gasometric. The polarographic method has also become widely known, which makes it possible to determine any oxygen concentration - from full saturation to 10-6 g / l. It makes it possible to continuously, automatically and almost instantly register the slightest changes in the concentration of dissolved oxygen. However, physicochemical methods are almost never used in mass analyzes due to their complexity and are usually used in scientific research.

1.2. Determination of dissolved oxygen in water.

Several methods are commonly used to determine dissolved oxygen in water. They can be divided into physicochemical and chemical.

Chemical methods for the determination of dissolved oxygen are based on the good oxidizing ability of this gas.

O 2 + 4H + → 2H 2 O

The Winkler method is commonly used.

1.2.1. Winkler's chemical method.

Among the methods for determining the concentration of dissolved oxygen, the oldest, but still relevant, remains the Winkler chemical method. In this method, dissolved oxygen quantitatively reacts with the freshly precipitated Mn (II) hydroxide. Upon acidification, a manganese compound of a higher valence releases iodine from the iodide solution in amounts equivalent to oxygen. The released iodine is further determined by titration with sodium thiosulfate with starch as an indicator.

The method has been known since 1888. Until the end of the twentieth century, the method of work was constantly being improved. It was only in 1970 that physicochemical methods of analysis began to be used to determine the content of oxygen dissolved in water. The chronology of the development of the Winkler method is presented in table 1.[ 3 ] ... Currently, the method has not lost its relevance, and now the main problem for improving the method is to improve the accuracy and the ability to determine low oxygen concentrations.

Table 1.

Chronological development of the Winkler method.

The essence of the method

The method is based on the oxidation of divalent manganese with oxygen to water-insoluble brown hydrate of tetravalent manganese, which, interacting in an acidic medium with iodine ions, oxidizes them to free iodine, quantitatively determined by a titrated solution of sodium hyposulfite (thiosulfate):

Mn 2+ + 2OH - ® Mn (OH) 2,

2Mn (OH) 2 + O 2 ® 2MnO (OH) 2,

MnO (OH) 2 + 2I - + 4H 3 O + ® Mn 2+ + I 2 + 7H 2 O,

I 2 + 2 Na 2 S 2 O 3 ® Na 2 S 4 O 6 + 2 NaI.

It can be seen from the equations that the amount of released iodine is equimolar to the amount of molecular oxygen. The minimum oxygen concentration determined by this method is 0.06 ml / l.

This method is applicable only to waters free of oxidizing agents (eg ferric salts) and reducing agents (eg hydrogen sulfide). The former overestimate, while the latter underestimate the actual amount of dissolved oxygen.

Sample selection

The oxygen sample should be the first sample taken from the bottle. To do this, after rinsing the oxygen bottle with water from the bottle, together with the rubber tube, a 10 cm long glass tube is inserted into the free end of the latter and lowered to the bottom of the oxygen bottle. Water is poured at a moderate rate to avoid the formation of air bubbles and one volume of the bottle is poured through its throat after filling. Without closing the bottle tap, carefully remove the tube from the bottle and only then close the tap. The bottle must be filled to the brim and free of air bubbles on the walls.

Immediately after filling, the dissolved oxygen is fixed, for which 1 ml of manganese chloride (or sulphate) and 1 ml of an alkaline solution of potassium iodide (or sodium) are successively introduced into the bottle. Pipettes with injected reagents must be lowered to half the height of the bottle. After the introduction of the reagents, the bottle is carefully closed with a stopper, avoiding the ingress of air bubbles, and the formed precipitate is vigorously stirred by turning the bottle 15–20 times until it is evenly distributed in the water. Then the flasks with the fixed samples are transferred to a dark place for settling. In this state, they can be stored for a maximum of a day at t< 10 ° С, and at a higher temperature no more than 4 hours.

Preparation for analysis

Reagents required for analysis

a) A solution of manganese chloride (or sulphate) is prepared by dissolving 250 g of salt in distilled water in a 0.5 liter volumetric flask.

b) To prepare an alkaline solution of potassium (or sodium) iodide, iodides must first be cleaned of free iodine, for which they are washed with rectified alcohol cooled to about 5 ° C on a filter funnel while stirring with a glass rod until an almost colorless portion of washing alcohol appears. The washed salt is dried in the dark between sheets of filter paper for a day and stored in well-closed jars (flasks) made of dark glass. Then they prepare:

Aqueous solution of potassium iodide (or sodium iodide)dissolving in distilled water 350 g KI (or 392 g NaI 2H 2 O) to a solution volume of 300 ml;

an aqueous solution of potassium hydroxide (or sodium hydroxide)dissolving 490 g of KOH (or 350 g of NaOH), respectively, in 360 and 340 ml of distilled water. The alkali should be weighed in a porcelain glass (or mug), where water is poured while stirring.

The resulting solutions of iodide and alkali are mixed with any cation and their volume is brought to one liter with distilled water in a volumetric flask. The resulting solution is stored in a bottle with a rubber stopper.

v) A solution of sulfuric acid 1: 4 is prepared by pouring in small portions one volume of concentrated sulfuric acid with a density of 1.84 to four volumes of distilled water in a porcelain glass with stirring.

G) To prepare a solution of 0.5% starch, 0.5 g of the "soluble starch" preparation is shaken in 15-20 ml of distilled water. The resulting suspension is gradually poured into 85-90 ml of boiling water and boiled for 1-3 minutes until the solution becomes clear. It is preserved by adding 1-2 drops of chloroform.

e) A 0.02 mol / L sodium thiosulfate solution is prepared by dissolving 5.0 g salt in CO-free 2 distilled water (free from CO 2 distilled water is prepared by boiling the latter for an hour. Then allow it to cool in the same flask (always with a stopper, "an absorbing tube with potassium or sodium alkali) in a liter volumetric flask or graduated cylinder, bringing the solution to the mark. It must be preserved by adding 3 ml of chloroform and stored in a dark glass bottle. with a stopper equipped with an absorbent tube filled with granular potassium or sodium alkali Prepare at the same time 3-5 liters of solution.

Determination of the correction factor for the molarity of sodium hyposulfite solution

Due to the instability of 0.02 mol / l sodium hyposulfite solution, it is necessary to periodically determine the correction factor to its normality. This should be done daily before starting the titration in continuous operation and before titrating each batch of samples with long breaks.

The correction factor is found when titrating iodate ions in an acidic solution:

IO 3 - + 5 I - + 6 H 3 O + ® 2 I 2 + 9 H 2 0,

6 S 2 O 3 2- + 2 I 2 ® 3 S 4 O 6 2- + 6 I -.

Therefore, one mole of iodate is equivalent to six moles of thiosulfate.

After dissolving 1 g of KI in 40-50 ml of distilled water, add 2 ml of sulfuric acid to a conical flask. Then, 15 ml of a solution of potassium iodate with a concentration of 0.0033 mol / L is poured in with a pipette, the flask is closed, gently stirred, and after keeping the solution for a minute, titration is started.

Until a light yellow color of the solution appears, titration is carried out without an indicator, after which 1 ml of starch solution and 50 ml of distilled water are added and titration is continued until the titrated liquid is completely discolored. The experiment is repeated 2-3 times, and if the discrepancy in the burette readings does not exceed 0.01 ml, the arithmetic mean is taken as the final result.

Interfering action of redox - active impurities.

Fe (II, III)

Ferrous iron compounds at the oxygen fixation stage can act as competitors with respect to manganese. Having reacted with oxygen, Fe (III) hydroxide is formed, the kinetics of its interaction with iodide in an acidic medium is slowed down. Thus, at an iron concentration of more than 25 mg / l, the use of the classical version of the Winkler method leads to an underestimation of the determination results. It was proposed to eliminate the effect of iron (III) by adding fluoride or using phosphoric acid when acidifying the sample. The resulting fluoride or phosphate complex prevents iron from interacting with iodide ions. But this method does not make it possible to eliminate the effect of ferrous iron.

Nitrite
Usually, the presence of nitrite in water is due to the microbiological conversion of ammonium to nitrate. And it is known that nitrites in an acidic medium are capable of oxidizing iodide ions, thereby causing overestimation of the results in the Winkler method. Nevertheless, when the content in water is up to 0.05-0.1 mgN / l, the direct Winkler method can be used. Sodium azide supplements are currently considered the most common way to neutralize the effects of nitrites. It should not be forgotten here that an excessive increase in the concentration of azide can lead to a negative error. This is due to the possibility of the reaction:

2 N 3- + 2 H + + J 2 = 2 HJ + 3 N 2

In addition to the use of azide, there are other ways to suppress or take into account the effect of nitrites: the use of urea or sulfamic acid. All of these reagents break down nitrite to molecular nitrogen.

Organic matter.

It is clear that the influence of organic substances, as pronounced reducing agents, will manifest itself at all stages of the determination of dissolved oxygen according to Winkler. Molecular oxygen, oxidized forms of manganese, molecular iodine are all strong enough oxidants to interact with organic impurities. If the water is rich in organic matter (oxidizability 15-30 mg O 2 / l and more), then it turns out to be necessary to introduce a correction for their interaction. For example, the manual proposes to conduct a parallel iodine test, thereby finding how much iodine was consumed for iodization of organic impurities. But there are methods that are based on the Winkler method, which differ from classical conditions (time of analysis, concentration of reagents). Thus, it is possible to select the conditions under which the interfering effect of the impurity can be neglected.

Sulfides and H 2 S.

It was found that the content of sulfides in the analyzed water leads to an underestimation of the results of the Winkler method. It was found that the interaction of sulfide with oxidants is stoichiometric: 1 mole of oxygen and 2 moles of sulfide. As a result of the reaction, elemental sulfur is released. Since in the Winkler method, in addition to oxygen, iodine and manganese (III, IV) are also strong oxidants, there are different opinions in the formulation of the mechanism of interaction of sulfide with an oxidizing agent. So in the work it is believed that sulfide interacts with oxidized forms of manganese. A method for the simultaneous determination of sulfides and oxygen in a water sample has been developed. The authors, using Zn salts, precipitate ZnS, which is then separated and determined spectrophotometrically, and dissolved oxygen is determined in the water remaining above the precipitate. In earlier work, a similar scheme was used, but not sulfate, but Zn acetate was used. When oxygen and sulfide react, thiosulfate can also be formed as an intermediate. The paper proposes a method for accounting for such a thiosulfate using the blank sample method.

In conclusion, it should be noted that along with modifications and techniques developed specifically for specific impurities, there are more general techniques aimed at determining the total content of reducing agents (Ross's method) and oxidizing agents.

To determine the presence of interfering substances in water, the following method is used.

Five milliliters of the sample is neutralized to pH = 7 with phenolphthalein and 0.5 ml is added. sulfuric acid. Then add a few grains, about 0.5 g, potassium iodide and starch.

A blue solution indicates the presence of oxidizing substances. If the solution is colorless, add 0.2 ml. iodine solution. Shake, leave for 30 seconds, if no blue color appears, therefore, there are reducing substances.

Methods for removing interfering substances during analysis.

1. In the presence of reducing agents, oxygen can be determined according to Ross: first, 0.5 ml is added to the oxygen bottle. sulfuric acid (1: 4), and then 0.5 ml. mixed reagent - hypochlorite and sodium sulfate, after which it is closed with a stopper, shaken and placed in a dark place for 30 minutes. To eliminate excess sodium hypochlorite, add 1 ml. potassium thiocyanate and stirred. In 10 minutes. Determine oxygen.

2. With iron content ( III ) less than 1 mg / l. Its influence is negligible. At a concentration of 1-50 mg / l. To dissolve the precipitate, orthophosphoric acid is required ρ = 1.70 g / cm 3 .

3. With a nitrate nitrogen content of more than 0.05 mg / L, it is difficult to determine soluble oxygen by the direct Winkler method, since nitrites in an acidic medium, acting as a catalyst, promote the oxidation of iodide to iodine by atmospheric oxygen, which leads to an increased consumption of thiosulfate and interferes with the end of titration, since the blue color of the indicator is restored. To eliminate the interfering effect of nitrites, you can use one of the following techniques:

Before dissolving the precipitate in acid, add a few drops of 5% sodium azide to the bottle;

Instead of sodium azide, 40% urea or sulfamic acid can be used. In this case, the order of addition of reagents changes: manganese hydroxide is precipitated with 70% potassium hydroxide or 50% sodium hydroxide, the precipitate is dissolved in acid, 0.15 ml of 40% sulfamic acid or urea is added and then 15% potassium iodide. Further, the definition is continued.

4. If the water contains many organic substances or mineral reductants, then it is necessary to introduce a correction for their iodine consumption. To do this, the test water is taken into two flasks of the same volume, each containing 3-5 ml of 0.02 m iodine in a saturated solution of sodium chloride. The flasks are closed with corks, mixed and after 5 minutes 1 ml of an alkaline solution of potassium iodide is added to both flasks, and then 1 ml of manganese salt into flask "a", 1 ml of distilled water into flask "b". Stopper and mix. After the sediment has settled, acid is added in the same amount to both flasks and titrated with iodine thiosulfate. The dissolved oxygen content is calculated by the formula:

X = 8 * n (A-B) * 1000 / V 1 - V 2,

where B is the volume of 0.02 N. thiosulfate solution used for titration of the solution in a bottle "b" ml; A - also for the bottle "a"; n. - the normality of the thiosulfate solution, taking into account the amendment; 8 - equivalent mass of oxygen; V 1 - the volume of the oxygen bottle, ml; V 2 - the volume of all reagents introduced into the water for the determination of oxygen, ml.

Accuracy of the direct Winkler method and its possible errors.

Throughout the first half of the 20th century, in the course of laboratory and field work, a large experimental base was collected based on the results of oxygen determination by the Winkler method. Discrepancies were found in the results of the determination of dissolved oxygen in the same waters by methods differing only in details, for example, the method of standardizing the thiosulfate solution, the concentration of reagents, the method of titration (the entire solution or aliquot), etc. This problem is largely the problem of standardizing the method Winkler, manifests itself in the variety of oxygen solubility tables. Differences in the tabular values ​​of oxygen solubility up to 6% contributed to research on the fundamental issues of the methodological basis and methodological errors of the Winkler method. As a result of such work, a number of potential sources of fundamental errors of the method in clean waters were formulated:

1. oxidation of iodide with atmospheric oxygen
2. volatilization of molecular iodine
3. the content of dissolved oxygen in the added reagents in the oxygen fixation procedure
4. admixture of molecular iodine in iodide
5. mismatch between the end point of titration and the equivalence point
6. low stability of sodium thiosulfate solutions and, accordingly, the need for frequent standardization
7. errors in standardization of sodium thiosulfate
8. difficulty in titrating small amounts of iodine
9. use of starch as an indicator: its instability and decrease in sensitivity with increasing temperature.

Let's dwell on the most significant errors. Oxidation of iodide with oxygen accelerates with increasing acidity. The influence of this process can be reduced by adjusting the pH of the medium. The recommended acidity value is pH = 2-2.5. Increasing the pH above 2.7 is dangerous because the process of manganese hydrate formation is already possible there. Simultaneously with the oxidation of iodide, the process of volatilization of iodine is also possible. Formation of a complex particle J 3 - under conditions of an excess of iodide (see the scheme of the Winkler method), it allows to bind almost all of the molecular iodine in the solution. It is clear that by introducing a solution of manganese salt and an alkaline reagent (alkali + iodide), we thereby introduce an unaccounted amount of oxygen dissolved in these reagents. Since reagents of different concentrations were used in various versions of the Winkler method, it was impossible to use any one correction in the calculations. It was necessary for each method to use its own calculated or experimental values ​​of oxygen introduced with the reagents. Typically, these values ​​were in the range of 0.005-0.0104 ppm.

By the mid-1960s, there was a need for a unified procedure for the determination of dissolved oxygen. This was partly due to the wide variety of chemical methods, the development of instrumental methods and the need for their intercomparison. Based on the published work, Carpenter formulated the Winkler oxygen determination procedure. In this version, almost all potential errors identified earlier were taken into account. In a joint work, Carrit and Carpenter supplemented this technique with a correction for taking into account the oxygen dissolved in the reagents (0.018 ml / l). The experimentally measured value was slightly different and amounted to 0.011 ml / l.

When determining the precision characteristics of Winkler's chemical method, researchers faced the problem of precisely setting the concentration of dissolved oxygen. To do this, we used the saturation of water with air or oxygen at a given temperature, the standard addition of an oxygen solution to deoxygenated water, the electrochemical generation of oxygen, and the use of alternative instrumental methods for the determination of oxygen. Despite the long history of this problem and numerous works, the final solution has not yet been found and the question is still open. The most popular way to set the oxygen concentration in water has been and remains to this day - the procedure for saturating water with atmospheric oxygen at a fixed temperature. However, the lack of uniformity of the procedure (solution volume, stirring conditions, method and rate of oxygen blowing) leads to significant errors, reaching 2%. This was manifested to a greater extent when working in the region of less than 5 mgO 2 / l.

Relying on the highly accurate preparation of oxygen solutions by introducing a standard additive into deoxygenated water, Carpenter managed to achieve 0.1% accuracy and 0.02% reproducibility at the 5 mgO level. 2 / L for a variant of the Winkler method with photometric titration. Table 2 shows the error of the classical version of the Winkler method at various levels of dissolved oxygen concentration.

Table 2.

The error of the Winkler method in clean waters.

Another important parameter that characterizes the capabilities of the method is the lower bound of the definition. Two values ​​of the lower limit are cited in the literature: ~ 0.05 and ~ 0.2 mgO2 / l. It is clear that the detection limit can be determined by the following criteria:

• violation of stoichiometry of reactions underlying the chemical basis of the Winkler method
• sensitivity of starch iodine reaction
• the concentration of the thiosulfate solution used and the resolution of the burette

1.2.2. Physicochemical method.

The method is based on amperometric studies. An oxygen concentration converter works by electrochemical reduction of oxygen entering its cathode through a selectively permeable membrane. The electric current generated in this case is proportional to the oxygen concentration in the analyzed environment.

A sensor submerged in the water to be analyzed, consisting of a chamber surrounded by a selective membrane, contains an electrolyte and two metal electrodes. The membrane is impermeable to water and dissolved ions, but oxygen is permeable. Due to the potential difference between the electrodes, oxygen is reduced at the cathode, and metal ions from solution at the anode.

The rate of the process is directly proportional to the rate at which oxygen passes through the membrane and electrolyte layer. And, consequently, the fractional pressure of oxygen in the sample at a given temperature.

2. EXPERIMENTAL PART.

2.1. Preparation of reagents.

We have prepared the following solutions

1. Manganese sulfate or chloride ( II ), solution. Dissolved 42.5 g. MnCl 2 * 4 H 2 O in distilled water and made up to 100 ml. Filtered through a paper filter. A diluted solution in an acidic medium with the addition of potassium iodide should not release free iodine.

2. Alkaline potassium iodide solution.

Dissolved 65.4 g of potassium iodide in 43.6 ml. distilled water. When acidified, the diluted solution should not release iodine.

Dissolved 305.2 g. KOH at 218 ml. distilled water. Both solutions were mixed and made up to 437 ml.

3. Sodium thiosulfate prepared from fixanal, 0.01923 N. solution (standardized K 2 Cr 2 O 7).

4. Potassium dichromate was prepared from a precisely known sample.

eq (K 2 Cr 2 O 7) = M (K 2 Cr 2 O 7) / 6,

where 6 is the number of electrons in a redox reaction.

10 ml. solution should contain 0.0003 eq. potassium dichromate.

1 eq. - 49.03 g.

0.0003 equiv. - x g. x = 0.0147 g.

then if 10 ml. contains 0.0147 g, then 1000 ml. - 1.47 g, which corresponds to 0.03 equiv. The sample was taken and leveled 1.4807 g, hence the normality of potassium dichromate = 0.0302 g.

5. Sulfuric acid, diluted 2: 1 solution.

2.2. Working out the technique.

To refine the method for determining oxygen in water, we carried out a number of studies.

Since there are no standard solutions, we tried to obtain water almost completely devoid of oxygen. To do this, we boiled distilled water for 3 hours. The results of determining oxygen in such water are shown in Figure 1.

Rice. 1.

Determination of oxygen in boiled water

We then oxygenated the remaining water. The saturation was carried out by bubbling air through water in a gasometer for three hours. The results of the analysis of the water obtained in this case are shown in Figure 2.

Rice. 2.

Determination of the oxygen content in oxygenated water after boiling.

The results we obtained for the analysis of water with a high oxygen content are more reproducible. This once again points to the difficulty of applying the method under conditions of low oxygen content in water.

2.3. Sampling and sample preparation

Typically, on-site samples are taken at three points (at both banks and in the fairway). Since the reservoir on which we conducted the research was rounded, we took samples along its banks, at the confluence of the Dubravenka River and at the place where the river flows out of it. Sampling was carried out from a depth of 10, 50 and 100 cm. Immediately after sampling, a corresponding entry was made in the logbook.

We assembled a bottle to take water samples. This device was a one-liter bottle with a rubber stopper attached to a pole. The batometer was lowered into the water to the required depth and the plug was pulled out. Taking the bottle out of the water, we measured the temperature. The pre-calibrated oxygen bottle was rinsed with water from a bottle and filled with a sample until approximately 200 ml of water poured out, i.e., until the water in contact with the air in the bottle was squeezed out. The bottle must be filled to the brim with the sample and free from air bubbles on the walls.

Then we add 1 ml of manganese chloride solution and 1 ml of an alkaline solution of potassium iodide to a bottle with a sample of water. In this case, you must use separate pipettes. Then quickly close the bottle so that no air bubbles remain in it, and mix the contents of the bottle thoroughly. Then the vials with the fixed samples were transferred to the laboratory in a dark place for settling.

2.4. Analysis of water for the content of dissolved oxygen.

All oxygen bottles were calibrated to the nearest 0.01 ml prior to analysis.

The resulting manganese hydroxide precipitate was allowed to settle for at least 10 minutes. Then poured in 5 ml of sulfuric acid solution. The displacement of a part of the transparent liquid from the bottle with a solution of sulfuric acid is not important for analysis. Close the bottle and mix thoroughly. The manganese hydroxide precipitate will dissolve.

After that, the entire sample was quantitatively transferred into a 250 ml conical flask and rapidly titrated with 0.01923 N. sodium thiosulfate with continuous stirring until a slightly yellow color, after which 1 ml of 0.5% starch was added and the titration was continued dropwise until the blue color disappeared. The color should disappear with one drop of thiosulfate.

Analysis results processing

C 1 = V 2 * C 2 * 8 * 1000 / V 1 - V 3,

V 1 is the total volume of the oxygen bottle (ml).

C 1 - oxygen concentration in the sample (mg / l.).

V 2 - the volume of sodium thiosulfate solution consumed for titration (ml).

C 2 - concentration of sodium thiosulfate solution (g-eq / l.).

8 is the atomic mass of oxygen.

1000 - conversion factor of units of measurement (from g. To mg.).

V 3 - the volume of water poured out during the introduction of reagents for fixing oxygen (ml).

Insignificant losses of dissolved oxygen in a bound form during the draining of excess liquid were neglected.

3. DISCUSSION OF RESULTS.

Rice. 3

Dependence of oxygen content in water on temperature.

The data we obtained are shown in Table 3.

Table 3.

The results of determining the concentration of oxygen,

dissolved in the water of the Dubravenka river.

The water in which the measurements were made had a temperature of 16.5 O C. The data show that the water is oversaturated with oxygen. In our opinion, this is due to the fact that at the point of sampling the river expands, forming a small lake, while the area of ​​contact of water with air and, accordingly, the saturation of water with oxygen increases. In addition, it should be noted that on the day of sampling it rained and, probably, this also allowed the water to be saturated with excess oxygen.

Based on the results of working out the method of work and the results of studies of natural water, we have developed guidelines for laboratory work to study the oxygen content in water. Methodological recommendations are given in Appendix 1.

CONCLUSIONS.

As a result of the work done by us:

• a method for determining the oxygen content in water has been worked out;
• The water of the Dubravenka river in the area of ​​its intersection with Mira avenue has been analyzed;
• Compiled guidelines for laboratory work on this topic.

Thus, we can draw conclusions:

1. The method for determining the oxygen content in water gives reproducible results in the region of high oxygen concentrations.
   1. Distilled water pre-saturated with oxygen can be analyzed to test the method.
   2. The method for determining oxygen dissolved in water can be used in a workshop on analytical chemistry on the topic "iodometric titration", in a workshop on methods of analyzing environmental objects, in a workshop on physical chemistry in the study of the equilibrium of dissolution of gases in liquids for the chemical specialty of our university, as well as in a workshop on hydrology, a geographic specialty.

LIST OF USED LITERATURE

1. Nekrasov 1.vol.
2. Ecology in chemistry lessons.
3. http://www.geocities.com/novedu/winkler.htm
4. http://www.oceanography.ru/library_archive/e_works/kaspy/metodhtml/oxygen/oxygen.htm

Research project on ecology for schoolchildren.

Work description: I bring to your attention a research work aimed at clarifying the quality of drinking water from various sources within the city: a well, a spring and a water supply system.

Target: Study of the quality of drinking water in the city of Kotovsk, Tambov region.
Tasks:
1. To master the method of determining the quality of drinking water.
2. Conduct a comparative analysis of water from different sources: well, spring and water supply
3. Conduct a survey among city residents about the sources of water they use.
Hypothesis: All the water we drink is drinkable.

Object of study: Well water, spring water and tap water.
Subject of study: Water quality.
During the research work passed the following stages:
1. Study of literature on this topic.
2. Choosing a topic of work, setting goals and objectives.
3. Water sampling for analysis.
4. Conducting a comparative analysis and water purification.
5. Systematization of results.
6. Registration of work.
To carry out this study, we used the following methods: study of popular science literature and Internet resources on this topic, generalization and systematization of information about water, sampling, analysis and purification of water, analysis of the work done, formulation of conclusions.

Experimental - experimental part.
Water analysis.
After conducting a survey among residents of the city, we found out what water sources they use. The main sources of water for the residents of the city are a water supply system, a spring, and a well.
We took water from these sources for comparative analysis.

Chromaticity:
water poured into a colorless glass is seen against the background of a white sheet of paper.
Spring is transparent.
Plumbing - turbid, reddish hue.
Well water is clear.

At this stage, we have put forward a hypothesis that the water from the spring, based on organoleptic characteristics, is drinkable.
During this stage of the study, we took the following steps:
- take an excursion to the Severny spring;
- to monitor the use of water from the spring for drinking purposes;
- take a water sample for analysis for research (is the water from the spring suitable for drinking purposes?);
- take the water from the spring for analysis to the laboratory of TOGBOU SPO KIT.
- to obtain analyzes of the study and compare them with the data of SanPiN 2.1.4. 1175-02 “Hygienic Requirements for Water Quality in Decentralized Water Supply. Sanitary protection of sources ".
The place of our research is located 250 meters west of the central part of our city of Kotovsk, in the forest, in the area of ​​the Boomerang cafe. It is characterized by the fact that the Tsna River in this section is 28 meters wide. The banks of the Tsna River are sandy, the left bank is gentle, the right bank is steep. Our fontanelle flows from the right bank. The spring flows into the Tsna River.
We identified the fact that within 2 hours 3 people came and filled 4 containers with water.
We provided water from this source to the laboratory for research.
Laboratory research data.

Chemical research of water.
RN 63
Total hardness - 5.0 mg eq / dm
Dry sediment - 255.0 mg / dm
Chlorides - 50.0 mg / dm
Sulfates - 57.0 mg / dm
Iron - 0.1 mg / dm
Oxidability - 5.3 mg / dm
Fluorine - 0.55 mg / dm
Ammonia - 0.19 mg / dm
Calcium - 37 mg / dm
Magnesium - 11.6 mg / dm
Nitrite - traces
Nitrates - traces
The result of the analysis showed compliance with the requirements of SanPiN 2.1.4. 1175-02 "drinking water" by chemical and organoleptic characteristics.

Sanitary and microbiological research.
OKB (common coliform bacteria) detected / norm-absence /
TMC (total microbial number) - 7 CFU
/ norm - up to 50 CFU /
TCB (thermotolerant coliform bacteria) detected / norm-absent

Based on the research data, we concluded:
bacteriological examination of water showed non-compliance with the requirements of SanPiN 2.1.4. 1175-02 "drinking water", because there is no sanitary protection zone, the spring is in close proximity to the river (spring water is mixed with river water), the spring must have a frame.
Our hypothesis was not confirmed, the water from this source is not drinkable.
Conclusion.
The research work carried out shows that not all water taken from sources in the vicinity of the city of Kotovsk is suitable for drinking. The purer, containing the least amount of impurities and foreign particles, is the water from the well. Tap water contains impurities of iron salts, and calcium salts are also in large quantities. Therefore, it is recommended to clean tap water before use. Spring water does not meet drinking water standards.
To determine the quality of drinking water from a water supply system and a well, we relied solely on organoleptic indicators, since these sources are appropriately equipped and in conditions of city water supply, the relevant utilities must monitor the state of water, and its composition is sufficiently stable. Nevertheless, we plan to carry out laboratory studies of water from these sources in the future.
The action "Live, spring!"

MCOU "Peregrebinskaya secondary school No. 1"

"Study of the chemical composition

tap water c. Crossbar

in a school laboratory "

Educational research work

Performed:Chernova Anna,

10th grade student

Supervisor:Lastaeva A.A. , chemistry teacher

with. Peregrebnoye, 2017

Study of the chemical composition of tap water in a school laboratory

Chernova Anna

with. Peregrebnoe, MCOU "Peregrebinskaya secondary school No. 1", grade 10

annotation

Water is the main chemical in the body. Human health depends on the quality of drinking water. In his work, in a school laboratory, the author analyzes the chemical composition of tap water, which includes a fractional method developed by Nikolai Aleksandrovich Tananaev, which makes it possible to detect a certain cation in a solution in the presence of a large number of other cations without resorting to their preliminary precipitation.

purpose of work : Determination of the chemical composition of tap water p. Crossroads in a school laboratory.

Tasks:

Examine the literature on the research topic

Find methods for determining the quality of tap water.

Identify factors affecting the quality of tap water

Find out the qualitative composition of tap water.

Compare the quality of tap water taken from different buildings p. Crossbar.

Subject of study : tap quality water

Object of study

Research methods:

1) empirical (observation, experiment, conversation)

2) theoretical ( analysis , generalization)

The author comes to the conclusion that the quality of tap water deteriorates as a result of movement through the water pipes, as evidenced by the difference in the results of water analysis in different buildings of the village.

This work can be used in chemistry lessons when studying the topics "Theory of electrolytic dissociation", "Salts".

RESEARCH PLAN

Everyone knows the truth from childhood thatwater is the source of life ... However, not everyone realizes and accepts the fact that water is the key to health and well-being. Everyone knows about the importance of water in our body.Water is the source of life , these are not just words. Present in all cells and tissues, playing a major role in all biological processes. Adults lose 3.5 liters of water every day. Therefore, our body constantly needs to replenish the supply of clean water.

Currently, the problems of various stages of drinking water supply are of great concern, including negative changes in the quality of drinking water in water distribution systems with centralized water supply. Consumption of poor quality drinking water leads to an increase in diseases. Most of us, despite all the threats and warnings of doctors, prefer tap water - collected in reservoirs from rivers and lakes, passed several levels of purification and fed through pipes to the tap. Some people purify it additionally at home using a filter, others buy clean drinking water in bottles. But let's see how we can be sure of what we drink? Does the quality of tap water in different areas correspond to c. Crossover to GOST requirements? Is it possible to determine the quality of water at home or in a school laboratory?

Hypothesis: 1) The quality of tap water can be determined in a school laboratory setting.

2) The quality of the water we use complies with GOST

Target: Determination of the chemical composition of tap water p. Crossover with centralized water supply in a school laboratory.

Tasks:

1. Examine the literature on the research topic

2. Find methods for determining the quality of tap water.

3. Identify factors affecting the quality of tap water

4. Find out the qualitative composition of tap water.

5. Compare the quality of tap water taken from different buildings with. Crossbar.

Subject of study : tap quality water

Object of study : chemical composition of tap water

Research methods:

1. Methods of empirical research : observation, experiment, conversation

2. Methods of theoretical research: analysis

Research tool: qualitative analysis, including the fractional method, which was developed by N.A. Tanaev. He discovered a number of new, original reactions that make it possible to detect a certain cation in a solution in the presence of a large number of other cations, without resorting to their preliminary precipitation.

Theoretical review of information on the research topic

Drinking water quality standards

The Ministry of Ecology of the Russian Federation compiles an annual rating of the best cities in Russia according to the compliance of the chemical composition of drinking water with the norm and a number of environmental indications. For example, in 2015, Kyzyl, Nizhnevartovsk, Glazov, Petrozavodsk, Khanty-Mansiysk (Annex 1) ... However, at the international level, when assessing the cleanest and highest quality water resource, Russia did not make it to the Top 10, giving way to Switzerland, Sweden and Norway. In this competition, the organoleptic, chemical, microbiological properties of water were assessed, which are taken into account when establishing regulatory parameters.

Russian regulatory documents also include quality requirements for organoleptic properties (with an assessment of odor, turbidity, taste, etc.), chemical composition (hardness, oxidizability, alkalinity, etc.), viral-bacteriological and radiological characteristics. The drinking water quality standards according to SanPiN and GOST, established for use, describe in detail the parameters of the content of chemicals(Appendix 2).

During the operation of water supply systems, responsibility for quality rests with a legal entity or an individual entrepreneur, who exercise control both at the points of water intake and at points of water intake, and at the intermediate stage of the resource entering the distribution network. Depending on the location, the rules regulate the frequency and number of checks.

At the points of water intake, microbiological and organoleptic samples from underground sources are taken at least 4 times a year (according to seasons); from surface sources - at least 12 times. Inorganic / organic samples from underground sources - once a year and from surface sources - every season. Radiological - regardless of the source - once a year.

Compliance with drinking water quality standards is determined with a high degree of certainty even at home. For this, portable analyzers are used, supplied with a ready-to-use set of reagents.

Factors affecting the quality of tap water

Sample studies before entering the water distribution network are carried out more often and depend on more factors

Operation of pumping and filtering stations

Purpose of pumping and filtering stations - cleansing (clarification) and disinfection of water.

Pumping and filtering stations(NSF) or wastewater treatment plants are complexes of treatment facilities, the composition of whichis determined by the quality of the source water, the requirements for water treatment and a number of other conditions (plant performance, features landscape, etc.).

Usually the NSF includes: pumping stations of the first and second lift, a disinfection system,sections of treatment facilities (mixers, flocculation chambers, horizontal sedimentation tanks, fast filter units ), clean water reservoirs and a block of auxiliary facilities (reagent facilities). Modern NSFs are suppliedsystems of automated control of technological process, significantly increasing the efficiency of their work.

In the village of Peregrebnoye, there are two NSFs. The water treatment plant purifies the water before it enters the water supply network of the village. Water disinfection occurs with ultraviolet light, which contributes to the growth of environmental safetywater treatment process.

The sewage treatment plant is used to purify water coming from the sewage network of the village. It was built in 2014. Productivity of each 1,000 cubic meters / day. Performance range 800 - 1200 m 3 / day ( Appendix 3)

Condition of water pipes

Sediments formed on the inner surface of pipelines are products of complex physicochemical processes occurring on it or on the applied protective coating, as well as in the water transported through the pipeline. In addition, deposits in pipelines in some cases are products of the vital activity of microorganisms that have settled and are present in water pipes due to the prevailing conditions.

The nature of deposits in pipelines is usually determined by:
- physicochemical properties of transported waters,

The operating conditions of the network,

- service life of pipelines

The smell of tap water can change for the worse for a number of reasons. Most often, the water begins to smell unpleasant due to the metal of the water pipes, excessive multiplication of microorganisms, chemicals used to fight harmful bacteria.

There are many reasons for an unpleasant odor. Most often, water changes its odor when exposed to cleaning chemicals. An equally common reason for the appearance of the problem under consideration is the poor quality of the water pipes.

The chemical composition of tap water and its effect on the human body

Half of the Russian population receives water that is hazardous to health. Contaminated water causes up to 80% of all known diseases and speeds up the aging process by 30%.Chemicals enter the human body not only through the direct consumption of water for drinking and food preparation, but also indirectly. For example, inhalation of volatile substances and skin contact while taking water treatments. The water flowing from our taps has a specific chemical composition. Chemicals contained in water can be divided into several groups: 1) substances that are most often found in tap water (fluorine, iron, copper, manganese, zinc, mercury, selenium, lead, molybdenum, nitrates, hydrogen sulfide);
2) substances remaining in water after reagent treatment: coagulants (aluminum sulfate), flocculants (polyacrylamide), reagents that protect water pipes from corrosion (residual tripolyphosphates), chlorine; 3) substances that enter water bodies with wastewater (household, industrial waste, surface runoff of agricultural land, which have been treated with chemical plant protection products: herbicides and mineral fertilizers); 4) components that can get into the water from water pipes, adapters, joints, welds, etc. (copper, iron, lead). All these substances can be both useful and hazardous to human health (Appendix 4)

WORK DESCRIPTION

Laboratory study of the chemical composition of tap water

For the study, 3 water samples were taken from different buildings in the village of Peregrebnoye.

Water samples : 1- reference water sample: still waterBonAqua, bottled in Samara, manufactured by Coca Cola

2- tap water st. Spasennikova 14aapartment 6

3- tap water st. Lesnaya 1b kV 11 (the sample was taken on February 14 after the water supply was turned off for 2 hours).

4- tap water lane. School, d 1 (chemistry room).

The following studies were carried out in the school laboratory:

within 6-9

Total mineralization (dry residue)

mg / l

1000 (1500)

1000

General hardness

meq / l

7,0 (10)

Permanganate oxidizability

mg O2 / l

5,0

Oil products, in total

mg / l

0,1

Surfactants (surfactants), anionic

mg / l

0,5

Phenolic index

mg / l

0,25

Alkalinity

mg HCO3 - / l

Aluminum (Al 3+ )

mg / l

0,5

s.-t.

0,2

Ammonia nitrogen

mg / l

2,0

s.-t.

1,5

Asbestos

million hair curls / l

Barium (VA 2+ )

mg / l

0,1

s.-t.

0,7

Beryllium (Be 2+ )

mg / l

0,0002

s.-t.

Boron (B, total)

mg / l

0,5

s.-t.

0,3

Vanadium (V)

mg / l

0,1

s.-t.

0,1

Bismuth (Bi)

mg / l

0,1

s.-t.

0,1

Iron (Fe, total)

mg / l

0,3 (1,0)

org.

0,3

Cadmium (Cd, total)

mg / l

0,001

s.-t.

0,003

Potassium (K + )

mg / l

Calcium (Ca 2+ )

mg / l

Cobalt (Co)

mg / l

0,1

s.-t.

Silicon (Si)

mg / l

10,0

s.-t.

Magnesium (Mg 2+ )

mg / l

s.-t.

Manganese (Mn, total)

mg / l

0,1 (0,5)

org.

0,5 (0,1)

Copper (Cu, in total)

mg / l

1,0

org.

2,0 (1,0)

Molybdenum (Mo, total)

mg / l

0,25

s.-t.

0,07

Arsenic (As, total)

mg / l

0,05

s.-t.

0,01

Nickel (Ni, total)

mg / l

0,1

s.-t.

Nitrates (by NO 3 - )

mg / l

s.-t.

50,0

Nitrite (by NO 2 - )

mg / l

3,0

3,0

Mercury (Hg, total)

mg / l

0,0005

s.-t.

0,001

Lead (Pb, total)

mg / l

0,03

s.-t.

0,01

Selenium (Se, total)

mg / l

0,01

s.-t.

0,01

Silver (Ag + )

mg / l

0,05

Hydrogen sulfide (H 2 S)

mg / l

0,03

org.

0,05

Strontium (Sr 2+ )

mg / l

7,0

org.

Sulfates (SO 4 2- )

mg / l

500

org.

250,0

Fluorides (F) for climatic regions I and II

mg / l

1,5 / 1,2

s.-t.s.-t.

1,5

Chlorides (Cl - )

mg / l

350

org.

250,0

Chromium (Cr 3+ )

mg / l

0,5

s.-t.

Chromium (Cr 6+ )

mg / l

0,05

s.-t.

0,05

Cyanides (CN - )

mg / l

0,035

s.-t.

0,07

Zinc (Zn 2+ )

mg / l

5,0

org.

3,0

Coliphages

Plaque-forming units (PFU) per 100 ml

Absence

Spores of sulfo-reducing clostridia

Number of spores in 20 ml

Absence

Giardia cysts

Number of cysts in 50 ml

Absence

Requirements for the organoleptic properties of water

Appendix 2

Rice.1 Sewage treatment plantFig. 2 Filtering device

Appendix 3

The effect of some chemical water pollutants on the human body .

Chlorine in tap water

Chlorine (Cl), or rather chlorine-containing compounds, is one of the main reagents used at water treatment plants for the disinfection and clarification of water entering the homes of Russians. Vchlorine forms hypochloric acid in waterandsodium hypochlorite... These chlorine-derived chemical compounds can be hazardous to health at high concentrations in water. Children are especially sensitive to the action of chlorine.
Small doses of chlorine can contribute to the development of inflammation of the mucous membrane of the mouth, pharynx, esophagus, and cause spontaneous vomiting. Water containing a large amount of chlorine has a toxic effect on the human body.

Aluminum in tap water

Aluminum (Al) present in natural water.Aluminum sulphate is widely used in water treatment processesas a coagulant, and its presence in drinking water is the result of insufficient control during these processes. When studying the effect of aluminum compounds on the human body, it was found thataluminum in large quantities can cause damage to the nervous system.
Magnesium in tap water

Magnesium (Mg) is also necessary for the human body, it is contained in every cell of the human body and is constantly introduced into the body with food and water. The negative effect of increased magnesium content on the human nervous system, magnesium ions, reversible depression of the central nervous system, the so-called magnesium anesthesia, was also revealed.

Iron in tap water

Iron (Fe)is one of the main elements of natural water. Other sources of iron in tap drinking water are iron-containing coagulants, which are used in water treatment processes. It can be iron that seeps into tap water from corroded areas of steel and cast iron water pipes. With an increased iron content in drinking water, it acquires a rusty color and a metallic taste. This water is unusable. Regular consumption of drinking water with a high iron content can lead to the development of a disease called hemochromatosis (deposition of iron compounds in human organs and tissues).

Calcium in tap water

Calcium (Ca) entering the body has a favorable human ability to densify cellular and intercellular colloids, as well as to influence the formation of the cell membrane. The ability of calcium ions to thicken the cell membrane and reduce cell permeability was revealed, which leads to a decrease in blood pressure, and with insufficient concentration of calcium ions, the intercellular adhesions dissolve, the walls of blood capillaries are loosened and the cell permeability increases, which leads to an increase in blood pressure.The positive role of calcium in the process of blood clotting is known..

Copper in tap water

Copper (Cu) levelin groundwater is quite low, but the use of copper in the components of a water supply system can lead to a significant increase in its concentration in tap water.Copper concentration over 3 mg / lcan cause acute dysfunction of the gastrointestinal tract. In people suffering from or having had liver disease (for example, viral hepatitis), the body's own exchange of copper is impaired.
Infants are most sensitive to high concentrations of copper in waterbottle-fed. Even in infancy, when drinking such water, there is a real, threat of liver cirrhosis.

Lead in tap water.

Sources of lead (Pb)drinking tap water can contain: lead dissolved in natural water; lead pollutants entering natural water through various routes (eg gasoline); lead contained in water pipes, adapters, welds, etc. Whendrinking water with a high content of leadacute or chronic poisoning of the human body can develop. Acute lead poisoning is dangerous and can be fatal. Chronic lead poisoning develops with the constant use of low concentrations of lead. Lead is deposited in almost all organs and tissues of the human body.

Zinc in tap water

Zinc (Zn)contained in almost all products, including water. It is present in it in the form of salts and organic compounds. Its contentin natural water does not exceed 0.05 mg / l, but its concentration in tap drinking water may be higher due to additional intake from water pipes.
The high content of zinc salts in drinking water can cause serious poisoning of the human body. Determined thatthe level of zinc salts in tap drinking water more than 3 mg / l makes it unusable

Consumption of poor-quality drinking water leads to an increase in diseases of both infectious and non-infectious nature associated with the chemical composition of the water. Violation of the above qualities of drinking water is observed with an unfavorable condition of surface water sources, low efficiency of water treatment, as well as an unsatisfactory condition of the inner surface of pipes of water distribution systems

Appendix 4

Odor character determination table