Analysis of drinking water quality in school laboratories. Studies of the mineral composition of water (carried out in the school laboratory). Factors affecting the quality of tap water

Introduction

Water "from the tap" is used by us everywhere. According to the laboratory of drinking water supply of the Research Institute of Human Ecology and the Environment of the Russian Academy of Medical Sciences, 90% of water supply networks supply water to homes that does not meet sanitary standards. The main reason for the presence of harmful nitrates, pesticides, oil products and salts of heavy metals in tap water is the catastrophic condition of the water and sewer systems. The combination of sewage water with emissions from enterprises gives an additional effect: bacteria - E. coli, pathogenic microorganisms, cholera vibrio, etc. are added to the above chemical components of drinking water. Therefore, the relevance of this problem is very high.

Object of study

The object of the study is ordinary tap water taken from the centralized source of water supply of the Lyceum No. 22, which was not subjected to any pre-treatment and filtration in order to be able to make an objective picture of the state of water used in everyday life.

Hypothesis

If the water is almost transparent, does not have a sufficiently pronounced taste and smell, and if the chlorine content, pH value and hardness of the water satisfy the MPC, then the water from the centralized water supply source is suitable for use.

Purpose of the study

In accordance with the hypothesis, the purpose of the study is to check whether tap water meets some of the requirements of GOST.

Literature review

A review of the literature on the impact of drinking water quality on health, drinking water quality standards and the formation of mutagens as a result of water chlorination was carried out.

Method "COMPOSITION AND QUALITY OF WATER"

The daily exchange of water in the human body is 2.5 liters, so the state of a person, his health and performance depends on its quality. Various substances present in the water give it a smell, make it either sweetish or salty or even bitter. There is a 5-point scale for assessing the intensity of the smell and taste of drinking water. If there is doubt about the quality of drinking water, special filters should be used to purify it from impurities.

The method of physical study of water includes:

Water transparency study
Determination of suspended particles in water
Smell
Taste.

These indicators are determined by special methods described in various sources of literature (for example, S.V. Druzhinin "Study of water and reservoirs in school conditions", 2008).

Chemical analysis method includes the definition:

Ions in water using qualitative reactions
pH, pH
Water hardness by titrimetric method.

Ion definition

Most of the known elements that make up relatively large amounts of water exist in the form of ions. To prove the presence of these ions in water, the technique of qualitative chemical semi-microanalysis was used. Qualitative analysis of water samples was carried out for the presence in water of: magnesium, iron(II,III), calcium, lead, copper cations; anions of bromine, iodine, chlorine, sulfate.

Hardness of water.

Water hardness is caused by the presence of calcium and magnesium salts in it. This is general hardness. It consists of carbonate (temporary, due to the presence of calcium and magnesium bicarbonates) and non-carbonate (permanent, due to the presence of calcium chlorides, Mg 2+ and Fe 2+). The salts remaining in the solution after boiling cause constant water hardness. The total hardness of water is determined as follows. Add 100 ml of test water to a 250 ml conical flask, add 5 ml of ammonia buffer solution (NH4OH + NH4Cl) to establish an alkaline reaction, and then 7-8 drops of an indicator (eriochrome black). The sample turns an intense cherry red color. The solution is stirred and slowly titrated with 0.05 normal solution of Trilon "B" until the color of the sample changes from cherry to blue. This is due to the fact that Trilon "B" in an alkaline environment interacts with calcium and magnesium ions, forming a complex uncolored compound and displacing the indicator in a free form. The calculation of the total stiffness is carried out according to the formula:

where: V is the volume of Trilon "B" solution used for titration, ml.

N - normality of Trilon "B" solution, mg equiv/l (0.05)

V 1 - the volume of the test solution taken for titration, ml. (100 ml)

Hydrogen index.

Water is tested with various indicators (litmus, universal indicator paper, methyl orange) and appropriate conclusions are drawn from the change in their color.

See the results in Table 1.

Comparative analysis of data obtained during the study.

It is given in the table "Compliance of physical and chemical indicators of water samples with the requirements of GOST".

Parameter	unit of measurement	Received value	Maximum allowable rate according to GOST 2874-82
Water transparency	5 point scale	1	1.5
Presence of suspended particles		1	2
The taste of water		1	2
The smell of water at t=20 o C The smell of water at t=60 o C		1	2
Hydrogen indicator	pH	~6.5	6.0 - 9.0
Rigidity	mol / m 3	~4.5	7.0

Conclusions.

In the course of the study, it was found:

The turbidity index is optimal
No suspended particles were found in the water
The water sample had no taste or odor
A qualitative analysis of a water sample gave a negative result for the presence in water of: magnesium, iron (II, III), lead, copper cations; anions, bromine, iodine; sulfates
Calcium cations (slight gypsum precipitation) and chloride anions (slight white curd silver chloride precipitation) were detected.
The reason for the slightly acidic environment is most likely, as established above, the presence of chloride ions in the water.
Water hardness was obtained in the range of 4-4.5 mmol/liter.

Thus, we can conclude that the water sample taken from the centralized source of water supply of Lyceum No. 22 meets the requirements of GOST according to the criteria by which the study was conducted, which means that our hypothesis was confirmed.

continue monitoring studies of the quality of drinking water from various sources;
to conduct a comparative analysis of the obtained results;
examine water samples according to quantitative analysis methods;
continue research in laboratory conditions provided with appropriate equipment and reagents.

Bibliography.

Bogolyubov A.S. Ecosystem. - M., 2001.
Newspaper "Biology". Publishing House "First of September". №23, 2008
Newspaper "Ivanovo-Press". No. 41 dated 10/11/2007
Popova T.A. Ecology at school. - M., 2005. - 64 p.
Website: www-chemistry.univer.kharkov.ua. Section: files, lecture 5 on ecology.
Website: www.ijkh.ivanovo.ru Section MUE "Vodokanal".
Website: www.prechist-ecologia.narod.ru Section "Water surface".
Fedoros E.I. Nechaeva G.A. Ecology in experiments. -M, 2006. - 384 p.

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

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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. . . 9

1.2.1. Winkler chemical method. . . . . . 9

1.2.2. Physical and chemical method. . . . . . 21

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

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

2.2. Development of the methodology. . . . . . . . 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

Appendix. . . . . . . . . 32

Introduction.

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

Oxygen is a strong oxidizing agent and reacts with many reducing substances. 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.

Often, the study of hydrochemical indicators of water bodies is carried out as part of special laboratory workshops at universities, as well as during school environmental monitoring. The amperometric method is of little use under these conditions. Conducting studies using the Winkler method requires the availability of simple and affordable methods for performing analyzes.

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

Tasks:

Conduct a literature review on methods for determining oxygen in water;
Work out the method of determination;
Prepare guidelines for conducting analyzes in a school setting.

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. About 23% of it is in the atmosphere, about 89% in water, about 65% in the human body, 53% oxygen in sand, 56% in clay, etc. If you calculate its amount in the air (atmosphere) , water (hydrosphere) and a part of the solid earth's crust accessible to direct chemical study (lithosphere), it turns out that oxygen accounts for approximately 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 immensity of this value, it does not exceed 0.0001 of the total oxygen content in the earth's crust.

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

Many life processes are associated with molecular oxygen. This substance supports the breath of most living beings living on the planet. In this regard, a vital task is to maintain the balance of molecular oxygen in the aquatic and air environment.

The binding of molecular oxygen occurs mainly due to oxidation reactions. In this case, molecular oxygen is transferred to the composition of other atmospheric gases, minerals, water, organic matter, etc.

Along with providing life 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 \u003d O 3

Ozone is an allotropic modification of oxygen and normal conditions is a gaseous substance. 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:

O 3 \u003d O 2 + O

The products of this reaction can react with each other to obtain the initial ozone. Thus, there is an equilibrium 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 is also quite large in water. 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 temperature the solubility of oxygen, like other gases, in water decreases. This distinguishes gases from most solids, which increase in solubility as the temperature of the solvent increases. 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, during the 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 the gas into a liquid solution.

At a given temperature, the number of such molecules is proportional to the gas pressure. Therefore, 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 \u003d K i + R i,

where С i is the gas concentration in the solution, P i is its partial pressure and Kі is 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 K i always the same, then the expression makes sense:

K \u003d C i1 / P i1 \u003d C i2 / P i2,

where С і1 and С і2 - concentration of dissolved gas at partial pressures, respectively Р i1 and P i2.

The partial pressure of oxygen in air will be:

P O 2 \u003d R 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 a constant temperature, 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 consumption, 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 proceeds as a result of 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 intense photosynthesis (in the photic layer), significant supersaturation is often observed sea water oxygen (sometimes up to 120-125% and above). With increasing depth, its concentration decreases due to the weakening of photosynthesis and consumption for the oxidation of organic substances and the 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 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, in violation of vertical circulation or the presence of a large amount of easily oxidized organic substances, the concentration of dissolved oxygen may drop to zero. Under such conditions, reduction processes begin to occur with the formation of hydrogen sulfide, as, for example, takes place 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 resulting oxidation reaction converts oxygen from its molecular form into other compounds, making it useless to support 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, the oxygen dissolved in water is determined by the Winkler volumetric method. Physicochemical methods are also used: electrochemical, gas chromatographic, mass spectrometric and gasometric. Also widely known is the polarographic method, which makes it possible to determine any concentration of oxygen, from full saturation to 10-6 g/l. It makes it possible to continuously, automatically and almost instantly record 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 the oxygen dissolved in water. They can be divided into physico-chemical and chemical.

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

O 2 + 4H + → 2H 2 O

Usually the Winkler method is used.

1.2.1. Winkler chemical method.

Among the methods for determining the concentration of dissolved oxygen, the oldest, but still not lost its relevance, remains the chemical method of Winkler. In this method, dissolved oxygen quantitatively reacts with freshly precipitated Mn(II) hydroxide. When acidified, a higher valency manganese compound releases iodine from the iodide solution in oxygen-equivalent amounts. 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 improved. And only in 1970, physico-chemical 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 ] . At present, the method has not lost its relevance, and now the main problem for improving the method is to increase the accuracy and the ability to determine low oxygen concentrations.

Table 1.

Chronological development of the Winkler method.

1888	Winkler's first publication of a new technique.
1920s	Inclusion of Winkler's method in Standard methods (1925). The appearance of the first chemical modifications.
1930-50s	Development of alternative instrumental methods(gasometric, photometric).
1960s	Learning the fundamental principles of the Winkler method. Attempts to develop a unified procedure for the determination of dissolved oxygen based on the work of Carrit and Carpenter.
1970s	Development of amperometric analyzers. GOST 22018-84, ST SEV 6130-87
1980s	Development of standards for the determination of dissolved oxygen based on the Carpenter variant. ISO 5813-83, ISO 5814-84.
1990s	The problem of calibration and comparison of methods for determining dissolved oxygen in the area of microconcentrations (less than 1 mgO 2 /l).

Method Essence

The method is based on the oxidation of bivalent manganese with oxygen to a water-insoluble brown hydrate of tetravalent manganese, which, interacting in an acidic environment 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 that do not contain oxidizing agents (for example, ferric salts) and reducing agents (for example, 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 with a rubber tube, a glass tube 10 cm long is inserted into the free end of the latter and lowered to the bottom of the oxygen bottle. The water is poured at a moderate rate to avoid the formation of air bubbles, and one volume of the bottle is poured down its throat after filling. Without closing the faucet of the bottle, carefully remove the tube from the bottle and only then close the faucet. The bottle should be filled to the brim and should not have air bubbles on the walls.

Immediately after filling, dissolved oxygen is fixed, for which 1 ml of manganese chloride (or sulfate) and 1 ml of an alkaline solution of potassium iodide (or sodium) are added to the flask in succession. Pipettes with injected reagents must be lowered to half the height of the bottle. After introducing the reagents, the flask is carefully closed with a stopper, avoiding the ingress of air bubbles, and the precipitate formed is vigorously stirred by turning the flask 15-20 times until it is evenly distributed in the water. Then the flasks with 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°C, and at a higher temperature no more than 4 hours.

Preparation for analysis

Reagents required for analysis

a) A solution of manganese chloride (or sulfate) 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 iodide (or sodium), iodides must first be purified from free iodine, for which they are washed with rectified alcohol cooled to about 5 ° C on a filter funnel with 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 dark glass jars (flasks). Then they prepare:

An aqueous solution of potassium iodide (or sodium iodide)dissolving in distilled water 350 g KI (or 392 g NaI 2H2 O) up to a solution volume of 300 ml;

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

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

v) A 1:4 sulfuric acid solution is prepared by pouring small portions of 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 0.5% starch solution, 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 of salt in CO-free 2 distilled water (free from CO 2 distilled water is prepared by boiling the latter for an hour. Then it is allowed to cool in the same flask (necessarily with a stopper, "an absorbent tube with potassium or sodium alkali) in a liter volumetric flask or volumetric cylinder, bringing the solution to the mark. It must be preserved by adding 3 ml of chloroform and stored in dark glass bottles with a stopper equipped with an absorption tube with granulated potassium or sodium alkali.At the same time prepare 3-5 liters of solution.

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

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

The correction factor is found by 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 potassium iodate solution with a concentration of 0.0033 mol/l is poured with a pipette, the flask is closed, gently mixed, 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 readings of the burette does not exceed 0.01 ml, the arithmetic mean is taken as the final result.

Interfering effect of redox active impurities.

Fe(II, III)

Ferrous iron compounds at the stage of oxygen fixation can act as competitors with respect to manganese. After reacting with oxygen, Fe(III) hydroxide is formed, the kinetics of interaction of which 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 results of the determinations. 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 influence of ferrous iron.

Nitrites
Usually the presence of nitrites in water is due to the microbiological conversion of ammonium to nitrate. And it is known that nitrites in an acidic environment are able to oxidize iodide ions, thereby causing an overestimation of the results in the Winkler method. However, up to 0.05-0.1 mgN/l in water, the direct Winkler method can be used. Currently, the most common way to neutralize the effect of nitrite is the use of sodium azide additives. It should not be forgotten here that an excessive increase in the azide concentration can also 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 account for the influence of nitrites: the use of urea or sulfamic acid. All these reagents destroy nitrite to molecular nitrogen.

organic substances.

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 sufficiently strong oxidizers 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 carry out a parallel iodine test, thereby finding how much iodine was consumed for iodization of organic impurities. But there are methods that are based on carrying out the Winkler method, under conditions different from classical ones (analysis time, reagent concentrations). Thus, it is possible to choose 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 oxidizing agents is stoichiometric: 1 mol of oxygen and 2 mol of sulfide. As a result of the reaction, elemental sulfur is released. Since, in addition to oxygen, iodine and manganese (III, IV) are strong oxidizing agents in the Winkler method, there are different opinions in formulating the mechanism of interaction of sulfide with an oxidizing agent. So in the work it is considered 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 in this work. 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 an earlier work, a similar scheme was used, but instead of sulfate, Zn acetate was used. In the interaction of oxygen and sulfide, the formation of thiosulfate is also possible, as an intermediate compound. The paper proposes a method for accounting for such thiosulfate using the blank sample method.

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

The blue color of the solution indicates the presence of oxidizing agents. If the solution is colorless, add 0.2 ml. iodine solution. Shake, leave for 30 seconds, if a blue color does not appear, therefore, there are reducing agents.

Methods for removing interfering substances in the analysis.

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

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

3. When the nitrogen content of nitrates is more than 0.05 mg / l, it is difficult to determine soluble oxygen by the direct Winkler method, since nitrites in an acidic environment, acting as a catalyst, contribute to the oxidation of iodide to iodine by atmospheric oxygen, which leads to an increased consumption of thiosulfate and prevents the end of the titration, since the blue color of the indicator is restored. To eliminate the interfering effect of nitrites, one of the following methods can be applied:

Before dissolving the precipitate in acid, a few drops of 5% sodium azide should be added to the flask;

Instead of sodium azide, 40% urea or sulfamic acid can be used. In this case, the order of adding 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. The definition continues.

4. If the water contains a lot of organic substances or mineral reducing agents, then it is necessary to correct for their iodine intake. To do this, the test water is taken into two flasks of the same volume, each with 3-5 ml of 0.02 m iodine in a saturated sodium chloride solution. The flasks are closed with stoppers, stirred, 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 is added to the flask "a", 1 ml of distilled water is added to the flask "b". Close with stoppers and mix. After the precipitate has settled, equal amounts of acid are added to both flasks and titrated with iodine thiosulfate. The content of dissolved oxygen is calculated by the formula:

X \u003d 8 * n (A-B) * 1000 / V 1 - V 2,

where B is the volume of 0.02 n. a solution of thiosulfate, which went to titrate the solution in the flask "b" ml; A - also for bottle "a"; n. is the normality of the thiosulfate solution, taking into account the correction; 8 is the equivalent mass of oxygen; V 1 is the volume of the oxygen bottle, ml; V 2 - the volume of all reagents added to the water to determine oxygen, ml.

The accuracy of the direct Winkler method and its possible errors.

Throughout the first half of the 20th century, a large experimental base was collected in the course of laboratory and field work based on the results of determining oxygen by the Winkler method. Discrepancies were found in the results of determinations of dissolved oxygen in the same waters according to methods that differ only in details, for example, the method of standardization of the thiosulfate solution, the concentration of reagents, the method of titration (the entire solution or an aliquot), etc. To a greater extent, this problem is the problem of standardizing the method Winkler, manifests itself in the variety of oxygen solubility tables. Differences in tabular values of oxygen solubility up to 6% contributed to research on fundamental issues 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 were formulated in clear waters:

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

Let's take a closer look at the most significant mistakes. Oxidation of iodide by oxygen accelerates with increasing acidity. The effect of this process can be reduced by adjusting the pH of the medium. The recommended value of acidity is pH=2-2.5. An increase in pH over 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 excess iodide (see the scheme of the Winkler method) allows you to bind almost all molecular iodine in solution. It is clear that by introducing a solution of a 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 different versions of the Winkler method, it was impossible to use any one correction in the calculations. For each method, it was necessary to use its own calculated or experimental values of the oxygen introduced with the reagents. Usually 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 great variety of chemical methods, the development of instrumental methods and the need for their mutual comparison. Based on the published work, Carpenter formulated the procedure for determining oxygen according to Winkler. In this version, almost all potential errors identified earlier were taken into account. In a joint work, Carritt and Carpenter supplemented this technique with a correction for oxygen dissolved in reagents (0.018 ml/l). The value experimentally measured in the work differed somewhat and amounted to 0.011 ml/L.

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

Relying on highly accurate preparation of oxygen solutions by adding a standard addition to deoxygenated water, Carpenter was able to achieve 0.1% accuracy and 0.02% reproducibility at the level of 5 mgO 2 /l for the variant of the Winkler method with photometric titration. Table 2 shows the accuracy of the classic version of the Winkler method at various levels of dissolved oxygen concentration.

Table 2.

The error of the Winkler method in pure waters.

mgO 2 /l	Error
0.05	~30%
0.2-0.3	10-20%
0.8-1.7	3-5%
3-...	~1%, but with careful work, a decrease to 0.1% is possible.

Another important parameter characterizing the possibilities of the method is the lower limit 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 limit of detection can be determined by the following criteria:

violation of the stoichiometry of the 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. Physical and chemical method.

The method is based on amperometric studies. The oxygen concentration converter works by electrochemical reduction of oxygen supplied to its cathode through a selective transmission membrane. At the same time generating electricity, is proportional to the oxygen concentration in the analyzed medium.

A sensor immersed in the analyzed water, consisting of a chamber surrounded by a selective membrane, contains an electrolyte and two metal electrodes. The membrane is impervious to water and dissolved ions, but permeable to oxygen. 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 of oxygen passing through the membrane and the electrolyte layer. And consequently - to the partial pressure of oxygen in the sample at a given temperature.

2. EXPERIMENTAL.

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 diluted to 100 ml. Filtered through a paper filter. A dilute solution in an acidic medium, when potassium iodide is added, should not release free iodine.

2. Alkaline solution of potassium iodide.

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

Dissolved 305.2 g. KOH in 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 an accurately 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 the redox reaction.

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

1 eq. - 49.03 g.

0.0003 equiv. - x g. x \u003d 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 equaled 1.4807 g, therefore the normality of potassium dichromate = 0.0302 g.

5. Sulfuric acid, diluted 2:1 solution.

2.2. Development of the methodology.

To develop the methodology for determining oxygen in water, we conducted a series of studies.

Since there are no standard solutions, we tried to obtain water that is 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. one.

Determination of oxygen in boiled water

After that, we oxygenated the remaining water. 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 water saturated with oxygen after boiling.

The results obtained by us for the analysis of water with a high oxygen content are more reproducible. This once again indicates the difficulties of applying the method in conditions of low oxygen content in water.

2.3. Sampling and sample preparation

Usually, samples in the section are taken at three points (near both banks and in the fairway). Since the reservoir on which we conducted the research had a rounded shape, we took samples along its banks, at the place where the Dubravenka River flows into it 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 journal.

To take water samples, we assembled a bathometer. This device was a liter bottle with a rubber stopper attached to a pole. The bathometer was lowered into the water to the desired depth and the cork was pulled out. Taking the bathometer out of the water, we measured the temperature. A pre-calibrated oxygen flask 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 that was in contact with the air in the flask was squeezed out. The flask should be filled to the brim with the sample and should not have air bubbles inside on the walls.

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

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

Prior to analysis, all oxygen bottles were calibrated to the nearest 0.01 ml.

The resulting precipitate of manganese hydroxide was allowed to settle for at least 10 minutes. Then 5 ml of sulfuric acid solution was added. The displacement of a part of the transparent liquid from the flask with a solution of sulfuric acid does not matter 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 continued dropwise until the blue color disappeared. The color should disappear with one drop of thiosulfate.

Processing of analysis results

C 1 \u003d V 2 * C 2 * 8 * 1000 / V 1 - V 3,

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

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

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

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

8- atomic mass oxygen.

1000 is the conversion factor for units of measurement (from g. to mg.).

V 3 - the volume of water that spilled out during the introduction of reagents for oxygen fixation (ml.).

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

3. DISCUSSION OF THE 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.

flask number	V thiosulfate, ml	V flasks, ml	C thiosulfate, equiv/l	C acid, mg/l
		106,99	0,01923
		105,88	0,01923
		108,88	0,01923
		108,78	0,01923
		105,74	0,01923
	6,18	107,52	0,01923
	6,12	106,11	0,01923
	6,05	105,23	0,01923
	5,94	102,99	0,01923
	6,18	106,69	0,01923

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

Based on the results of working out the methodology of work and on the basis of the results of studies of natural water, we developed guidelines for laboratory work on the study of the oxygen content in water. Guidelines are given in Appendix 1.

CONCLUSIONS.

As a result of our work:

a method for determining the oxygen content in water has been developed;
The water of the Dubravenka River was analyzed in the area of its intersection with Mira Avenue;
Guidelines for conducting laboratory work on this topic have been compiled.

Thus, we can conclude:

The method for determining the oxygen content in water gives reproducible results in the region of high oxygen concentrations.
1. To refine the technique, distilled water preliminarily saturated with oxygen can be analyzed.
2. The method for determining oxygen dissolved in water can be used in the workshop on analytical chemistry on the topic "iodometric titration", in the workshop on methods of analyzing environmental objects, in the 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 of a geographical specialty.

LIST OF USED LITERATURE

Nekrasov 1. volume
Ecology at chemistry lessons.
http://www.geocities.com/novedu/winkler.htm
http://www.oceanography.ru/library_archive/e_works/kaspy/methodhtml/oxygen/oxygen.htm

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Introduction

Object of study

Hypothesis

Purpose of the study

In accordance with the hypothesis, the purpose of the study is to check whether tap water meets some of the requirements of GOST.

Literature review

A review of the literature on the impact of drinking water quality on health, drinking water quality standards and the formation of mutagens as a result of water chlorination was carried out.

Method "COMPOSITION AND QUALITY OF WATER"

The method of physical study of water includes:

Water transparency study
Determination of suspended particles in water
Smell
Taste.

These indicators are determined by special methods described in various sources of literature (for example, S.V. Druzhinin "Study of water and reservoirs in school conditions", 2008).

Chemical analysis method includes the definition:

Ions in water using qualitative reactions
pH, pH
Water hardness by titrimetric method.

Ion definition

Hardness of water.

where: V is the volume of Trilon "B" solution used for titration, ml.

N - normality of Trilon "B" solution, mg equiv/l (0.05)

V 1 - the volume of the test solution taken for titration, ml. (100 ml)

Hydrogen index.

Water is tested with various indicators (litmus, universal indicator paper, methyl orange) and appropriate conclusions are drawn from the change in their color.

See the results in Table 1.

Comparative analysis of data obtained during the study.

It is given in the table "Compliance of physical and chemical indicators of water samples with the requirements of GOST".

Parameter	unit of measurement	Received value	Maximum allowable rate according to GOST 2874-82
Water transparency	5 point scale	1	1.5
Presence of suspended particles		1	2
The taste of water		1	2
The smell of water at t=20 o C The smell of water at t=60 o C		1	2
Hydrogen indicator	pH	~6.5	6.0 - 9.0
Rigidity	mol / m 3	~4.5	7.0

Conclusions.

In the course of the study, it was found:

The turbidity index is optimal
No suspended particles were found in the water
The water sample had no taste or odor
A qualitative analysis of a water sample gave a negative result for the presence in water of: magnesium, iron (II, III), lead, copper cations; anions, bromine, iodine; sulfates
Calcium cations (slight gypsum precipitation) and chloride anions (slight white curd silver chloride precipitation) were detected.
The reason for the slightly acidic environment is most likely, as established above, the presence of chloride ions in the water.
Water hardness was obtained in the range of 4-4.5 mmol/liter.

continue monitoring studies of the quality of drinking water from various sources;
to conduct a comparative analysis of the obtained results;
examine water samples according to quantitative analysis methods;
continue research in laboratory conditions provided with appropriate equipment and reagents.

Bibliography.

Bogolyubov A.S. Ecosystem. - M., 2001.
Newspaper "Biology". Publishing House "First of September". №23, 2008
Newspaper "Ivanovo-Press". No. 41 dated 10/11/2007
Popova T.A. Ecology at school. - M., 2005. - 64 p.
Website: www-chemistry.univer.kharkov.ua. Section: files, lecture 5 on ecology.
Website: www.ijkh.ivanovo.ru Section MUE "Vodokanal".
Website: www.prechist-ecologia.narod.ru Section "Water surface".
Fedoros E.I. Nechaeva G.A. Ecology in experiments. -M, 2006. - 384 p.

Living water. Assessment of the quality of spring water.

Introduction

At present, the problem of drinking water quality has become the main component of the country's security. Despite the huge number of organizations that control water quality at the departmental and state level, firms and factories involved in the development and sale of filters for water purification, pouring water into containers, man-made disasters have become more frequent, people are massively infected through water with infectious diseases, suffer from pollution of drinking water sources. water supply with either oil products or pesticides. The problem of drinking water quality is an important environmental problem, it attracts more and more attention of the population.

The problem of drinking water quality in the village of Iglino is one of the most urgent at the moment. V Lately more and more often among the villagers there is a question about the quality tap water not only in people's conversations, but also on the pages of the regional newspaper.

Is it possible to solve the problem of lack of drinking water by cleaning and restoring springs? How do people today relate to spring water and what is its quality?

In our opinion, the study of springs, their examination, certification, practical work on protection - necessary condition regulation of accumulated environmental issues our society. Groundwater, although hidden from view, but their role is great both in nature and in human life. Springs are important sources of river nutrition, participate in the formation of the relief, supply plants with moisture, are used for local water supply, and often, with sufficient power, for supplying water pipes. Groundwater, compared to surface water, contains less pathogenic bacteria, is less susceptible to pollution, and often does not require special treatment.

The purpose of our work: study the condition of a nearby spring. Determine whether this water can be used for drinking, whether it carries any health hazard.

Tasks:

analyze the spring water;

establish compliance of water quality with sanitary standards;

gain experience in determining the environmental criteria for the state of the spring, the degree of pollution;

This research will provide information on the state of the water quality of the spring, draw public attention to the problem of water pollution, shallowing and disappearance of springs.

Relevance of the topic:

Water is the most common substance on the planet. It occupies most of our planet. All living organisms are almost 90% water. In the human body, water is involved in all vital important processes. The large reserves of water on our planet give the impression of its inexhaustible abundance. But, different state and the different qualities of water, as well as the peculiarities of its circulation on Earth, lead to the fact that only an insignificant part of the water reserves is available and suitable for practical use.

Groundwater is the only type of mineral resource that can be renewed during operation, as it is a complex dynamic system that interacts with the environment.

Despite all this, there is a problem of clean water on our planet.

The water from the spring is used by the villagers for drinking.

Research methods:

selection and study of literature on the research question;

conducting a pilot study;

Location of the study: a spring and the territory adjacent to it in the Mryaevo microdistrict of the village of Iglino.

Terms of the study: September - October 2013.

Research methodology

The analysis of water from wells, springs and other surface sources differs from the analysis of water from wells or aqueducts, since pollutants such as nitrates and nitrites are of particular importance in surface waters, but practically no sulfates, for example, are found in wells. Surface water should also be tested for the presence of pathogens. Specialists of the Main Testing Center for Drinking Water recommend a scheme of 20 basic chemical indicators and three bacteriological indicators for the analysis of water from wells and springs: total iron, mg/dm3; calcium, mg/dm3; magnesium, mg/dm3; sodium, mg/dm3; potassium, mg/dm3; nitrates, mg/dm3; nitrites, mg/dm3; alkalinity, mmol/dm3; bicarbonates, mg/dm3; total hardness, ° W; pH value (pH), units; turbidity, IU/dm3; chromaticity, degrees; taste, points; smell, points; permanganate oxidizability, mg/dm3; ammonia (for nitrogen), mg/dm3; chlorides, mg/dm3; fluorides, mg/dm3; total mineralization, mg/dm3.

We used methods available for implementation in the framework of the school chemical laboratory.

Methods for determining indicators characterizing the properties of spring water.

1. Physical methods for determining indicators characterizing the organoleptic properties of water.

Organoleptic properties are normalized according to the intensity of their perception by a person. These are temperature, color, transparency, turbidity, sediment, smell, taste, impurities.

Determination of water temperature.

Equipment: water thermometer with a division value of 0.1 ° C.

Progress: Immerse a water thermometer in water just taken from a spring for five minutes. Without removing the thermometer, determine the temperature of the water.

Study of the color of water.

The color of water depends on the presence of impurities of mineral and organic origin in it - humic substances, humus, which are washed out of the soil and give the water a color from yellow to brown. Iron oxide colors water yellow-brown and brown, clay impurities yellowish. The color of the water may be due to sewage or organic matter. .

Equipment: glass vial.

Progress: Pour 8-10 ml into a transparent glass tube. test water and compare with a similar column of distilled water. Examine it in the light, determine the color.

Evaluation of results: chromaticity is expressed in degrees, using a table. (Appendix).

Determination of water transparency.

The transparency and turbidity of water is determined by its ability to transmit visible light. The degree of transparency of water depends on the presence of suspended particles of mineral and organic origin in it. Water with a significant content of organic and mineral substances becomes cloudy. Turbid water is poorly disinfected, it creates favorable conditions for the preservation and development of various microorganisms, including pathogens. A measure of transparency is the height of the water column, through which it is still possible to distinguish a font of a certain size and type on white paper. The method gives only indicative results.

Equipment: glass graduated cylinder with a flat bottom; standard font with letter height 3.5 mm.

Progress: the determination is carried out in a well-lit room, but not in direct light, at a distance of 1 m from the window. The cylinder is placed motionless above the standard font. The cylinder is filled with a well-mixed sample of the water to be studied, keeping the font clear until the letters viewed from above become poorly distinguishable. The height of the water column in centimeters through which the text can be read is considered the water transparency value.

Evaluation of results: the measurement is repeated 3 times and the final result is taken as the average value measured with an accuracy of 0.5 cm. Water is transparent, slightly transparent, opaque in terms of transparency. So, the transparency of drinking water should be at least 30 cm.

Turbidity study.

Equipment: glass vial.

Progress: shake the water and pour it into a test tube so that the height of the water is 10 cm, examine the water in the light, determine the level of turbidity.

Evaluation of results: water turbidity can be weak, noticeable, strong.

Study of water sediment.

Equipment: glass vial.

Progress: examine the water under study in the light.

Evaluation of results: water sediment is characterized: quantitatively - by the layer thickness; in relation to the volume of the water sample - negligible, insignificant, noticeable, large; qualitatively - by composition: amorphous, crystalline, flaky, silty, sandy.

Determination of the smell of water.

The smell is evaluated in points. Odorless water is considered to be water whose odor does not exceed 2 points. The smell is primarily due to sulfur- and nitrogen-containing organic compounds formed as a result of the decomposition of organic matter (usually dead plants or excrement) in anoxic and low-oxygen conditions. Water with a pronounced odor is unsuitable for the life of microorganisms, as it is either poisonous or does not contain oxygen.

Equipment: conical flask with a capacity of 150–200 ml.

Progress: 100 ml of test water at room temperature is poured into a flask. Cover with a ground cork, shake with a rotary motion, open the cork and quickly determine the nature and intensity of the odor. The flask is then heated to 60° C. in a water bath and the odor is also evaluated.

The intensity of the smell of water is determined at 20 and 60 0 C and evaluated on a five-point system according to the requirements of the table. The smell of drinking water should not exceed 2 points

Evaluation of results: the smell is determined in points, a table is used. (Appendix).

Determining the taste of water

The assessment of the taste of water is carried out for drinking natural water in the absence of suspicions of its contamination. There are 4 tastes: salty, sour, bitter, sweet. The rest of the taste sensations are considered flavors (salty, bitter, metallic, chlorine, etc.)

Progress: when determining the taste and taste, the analyzed water is taken into the mouth (after the smell is determined) and held for 3–5 seconds without swallowing. After determining the taste, the water is spit out.

Evaluation of results: the intensity of taste and taste is evaluated on a 5-point scale. For drinking water, values of indicators of taste and taste of not more than 2 points are allowed. (Appendix).

Particulate matter detection.

This indicator of water quality is determined by filtering a certain volume of water through a paper filter and then drying the filter cake in an oven to constant weight.

Equipment: flask, filter, funnel, balance, drying cabinet.

Progress: for analysis, take 500-1000 ml of water and filter it. The filter is weighed before use. After filtration, the filter cake is dried to constant weight at 105° C. and cooled.

Evaluation of results: the cooled precipitate with the filter is weighed.

2. Chemical methods for determining the quality of water.

Determination of water hardness.

Equipment: plastic bottle, soap solution.

Progress: draw 2/3 of the water from the spring into the bottle, add soapy water and shake.

Evaluation of results: if the foam is abundant - the water is soft, if the foam does not grow “curled up” - the water is hard.

Determination of the hydrogen index of water (pH).

V natural waters The pH ranges from 6.5 to 9.5. the norm is 6.5–8.5. If the pH of the water is below 6.5 or above 8.5, then this indicates that it is contaminated with sewage.

Water heavily polluted with organic matter of animal origin and decay products usually has an alkaline reaction (pH> 7), and water polluted with sewage industrial enterprises, – acidic (pH<7).

Equipment: water samples, universal indicator paper; colored pH scale.

Progress: take a water sample from a spring. Moisten the indicator paper in the test water and compare its color with a standard paper color indicator scale. The exposure time of paper in water is about 20 seconds.

Evaluation of results: pH is determined using universal indicator paper, comparing its color with a scale.

a) If the concentration of hydrogen ions H + and hydroxide ions OH - in water is the same, its pH = 7, the aqueous medium is considered neutral;

b) If there are more H+ ions than hydroxide ions, then pH<7, вода имеет кислотную реакцию;

c) If the concentration of hydroxide ions exceeds the concentration of H + ions, then pH> 7, such water has a basic or alkaline reaction.

Determination of the content of iron ions.

Equipment: water samples, concentrated nitric acid, 20% ammonium thiocyanate solution.

Progress: take a water sample from a spring. In 10 ml of water add 2 drops of concentrated nitric acid and 1 ml of 20% ammonium thiocyanate solution. Mix everything and visually determine the approximate concentration of iron according to the table.

Evaluation of results: visual determination of the approximate concentration of iron in the test solution.

Determination of the content of chlorine ions

A lot of chlorides get into water bodies with household and industrial wastewater discharges. The amount of chlorides depends on the nature of the rocks that make up the basins. Chloride ions can be detected with a 10% silver nitrate solution.

Equipment: 10% silver nitrate solution, test tube.

Progress: Pour 5 ml into a test tube. test water and add 3 drops of 10% silver nitrate solution.

Evaluation of results: the approximate content is determined by sediment or cloudiness. Turbidity will be the greater, the greater the concentration of chloride ions in the water. The MPC of chlorides in water bodies is allowed up to 350 mg / l.

Determination of the content of sulfate ions.

Equipment: 5% barium chloride solution, hydrochloric acid solution, test tube.

Progress: 10 ml of test water is added to the test tube, 2–3 drops of hydrochloric acid are added, and 0.5 ml of barium chloride solution is added.

Evaluation of results: according to the nature of the precipitate, the approximate content of sulfates is determined: in the absence of turbidity, the concentration of sulfate ions is less than 5 mg-l; with a weak turbidity that appears after a few minutes - 5-10 mg-l; with a weak turbidity that appears immediately - 10–100 mg-l; strong, rapidly settling turbidity indicates a fairly high content of sulfates (more than 100 mg-l). MPC of sulfates in reservoirs - sources of water supply is allowed up to 500 mg / l.

Research results

As a result of our studies of the quality of water from the spring, we obtained the following experimental data (Table 1, Table 2).

With the help of physical methods, indicators characterizing the organoleptic properties of water were determined.

Table 1.

Organoleptic properties of spring water

Location of the spring

Mryaevo microdistrict.

t°C water

Chroma

Turbidity

Transparency (cm)

35 cm

Amount of sediment (mm)

Sludge quality

Odor intensity

Smell quality

Weigh. particles

0.026 g

Table 2.

The results of the analysis of chemical indicators of spring water

General hardness

Presence of ions

Ca2+

Mg 2+

SO 4 2-

CO 3 2-

Fe2+

CL-

hg +

soft

less than 5mg/l

less than 0.05

Conclusion: the water from the spring is cool, transparent, odorless and tasteless, colorless in a thin layer, and pigeon-colored in a thick layer, does not contain harmful impurities - it is suitable for drinking.

conclusions

Water from a spring located in the Mryaevo microdistrict of the village of Iglino, which we studied using physical and chemical methods available in the school chemical laboratory, is cool, transparent, odorless and tasteless, colorless in a thin layer, and blue in color in a thick layer, does not contain harmful impurities in the form of chlorine ions, sulfate ions, iron ions.

Based on the work carried out, it can be concluded that the water from this source can be used in everyday life, suitable for drinking, since it does not have visible pollution. We did not conduct a study of water for the presence of pathogens in it. D Additional research is needed to answer this question.

The spring we studied is of great importance for the local
water supply, especially for residents of Yakutova Street, when the central water supply is turned off, residents of this street use the spring water for food and for other purposes.

Conclusion

Water plays a very important role in the life of plants, animals and humans. The need of the population for clean, transparent, colorless, tasteless and odorless drinking water is quite obvious. In my work, I selected and mastered experimental methods that allow to identify the organoleptic and physico-chemical properties of water, conducted a study of the water quality of one of the springs in our area. A chemical analysis of water samples was carried out: hardness, pH, and the content of iron ions, sulfate - and chloride - ions were determined. All data were compared with MPC in accordance with GOST 2874-73 and GOST 2874-82. Research work was carried out in the office - laboratory of chemistry MBOU secondary school No. 2 (Appendix).

The results obtained were analyzed. According to the results of the analysis, the spring water can be considered environmentally safe.

The more you learn about the springs, the more secrets are revealed, the more questions arise. For example, why spring water is called "living". Is it because it is very pure, and we have already lost the habit of it, or because it has a favorable composition for the body, physical structure and magnetic field? Is it because, taking water from a spring, we come into contact with nature, we hear the murmur of water? And, perhaps, due to some other, yet unknown to us reasons.

Bibliography

1. Ashikhmina T. A. "School environmental monitoring" - "Agar".

Rendezvous-AM 2000
2. Argunova M. V. “Methods of educational environmental monitoring”, scientific and methodological journal “Chemistry at School” 2’2009.

4. Edited by L. A. Korobeynikova "Environmental monitoring at school". Edition 2nd. - Vologda 2000
5. http://ru.wikipedia.org
6. http://www.vitawater.ru

Research work "Comparative chemical analysis of water in the village of Tukaevo and the city of Tarko-Sale"

Supervisor: Nasyrova Albina Galiullovna
The work was done by a 10th grade student Elza Adelmetova
Description: This work was presented at the republican scientific-practical conference "Pure Science"

The reason for writing this work was a trip to the city of Tarko-Sale. During my stay in this city, I was surprised by the fact that they do not have scale on the walls of the kettle. From the course of chemistry, I know that scale is a consequence of the use of hard water.
Water directly affects human health, and we decided to answer the questions: what kind of water flows from our tap? What substances are contained in it? What is the difference between the water of the village of Tukaevo and the water of the city of Tarko-Sale? With what it can be connected?
Based on the foregoing, it was purpose of the research work: conduct a comparative chemical analysis of water in the village of Tukaevo and the city of Tarko-Sale in a school laboratory and compare the results.
Object of study:
- water from the village of Tukaevo
- water of Tarko-Sale
Research methods:
- Literature review
- Physical and chemical analysis of water
- Comparison
Practical significance This work consists in creating a presentation, issuing a brochure, an educational newspaper.

Chemical components of water
Chemical components of natural waters are conditionally divided into 5 groups: 1) Main ions; 2) dissolved gases; 3) biogenic substances; 4) trace elements; 5) organic matter
Comparative chemical analysis of water in the village of Tukaevo and the city of Tarko-Sale
I Organoleptic indicators of water
1. Color (painting)
Color diagnostics is one of the indicators of the state of water.
To determine the color of water, we took a glass vessel and a sheet of white paper. Water was taken into the vessel and the color of the water (colorless, green, gray, yellow, brown) was determined on a white background of paper - an indicator of a certain type of pollution.
In the analysis of both samples, the water was colorless, which means that the water is suitable for drinking.
2.Transparency
To determine the transparency of water, we used a transparent measuring cylinder with a flat bottom, into which we poured water, then placed a font under the cylinder at a distance of 4 cm from its bottom, the height of the letters of which was 2 mm, the thickness of the lines of the letters was 0.5 mm, and drained the water to until this font became visible from above through a layer of water. We measured the height of the remaining water column with a ruler and expressed the degree of transparency in centimeters. When water transparency is less than 3 cm, water consumption is limited.
In the drinking water of both samples, the water transparency is 10 cm
3.Smell
The smell of water is due to the presence of odorous substances in it that enter it naturally and with sewage. The smell of water should not exceed 2 points. The odor intensity was determined according to the table:
Score Odor intensity Qualitative characteristic
0 - No perceptible odor
1 Very weak Odor not detectable by the consumer but detectable in the laboratory by pilot testing
2 Slight Odor that does not attract the attention of the consumer, but detectable if you pay attention to it
3 Perceptible Smell that is easily detectable and gives rise to disapproval of water
4 Distinctive Smell that attracts attention and makes water undrinkable
5 Very strong The smell is so strong that the water becomes undrinkable.

The smell of water was determined in a room in which there was no foreign smell. In the drinking water of both samples, there is no smell, which means that it is suitable for drinking.
II Chemical analysis of water
1.Hydrogen index (pH)
Drinking water should have a neutral reaction (pH about 7).
The pH value was determined as follows. 5 ml of the test water, 0.1 ml of a universal indicator were poured into a test tube, mixed and the pH was determined by the color of the solution: the water solution from the village of Tukaevo turned light yellow - a neutral medium, and the water from the city of Tarko-Sale turned pink-orange - alkaline environment.
Pink-orange - pH about 6;
Light yellow - 7;
Greenish-blue - 8.
2. Determination of chloride ions
The concentration of chlorides is allowed up to 350 mg/l.
5 ml of the studied water from the village of Tukaevo and the city of Tarko-Sale were poured into a test tube and 3 drops of a 10% solution of silver nitrate were added. Approximate chloride content was determined by sediment or cloudiness.
Determination of chloride content
Precipitate or turbidity Concentration of chlorides, mg/l
Weak haze 1-10
Strong haze 10-50
Flakes form, but do not settle immediately 50-100
White voluminous precipitate More than 100

In the drinking water of the village of Tukaevo, a white voluminous precipitate (more than 100 mg/l) fell out.
In the second sample of drinking water from the city of Tarko-Sale, a slight turbidity (1-10 mg/l) was observed.
3. Determination of sulfates.
10 ml of test water, 0.5 ml of hydrochloric acid (1:5) and 2 ml of 5% barium chloride solution were added to the test tube, mixed. The approximate content of sulfates was determined by the nature of the precipitate. In the absence of turbidity, the concentration of sulfate ions is less than 5 mg/l; with weak turbidity, which does not appear immediately, but after a few minutes, - 5-10 mg / l; with a weak turbidity that appears immediately after the addition of barium chloride - 10-100 mg / l; strong, rapidly settling turbidity indicates a fairly high content of sulfate ions (more than 100 mg/l).
In the first water sample from the city of Tarko-Sale, a slight turbidity was observed, which did not appear immediately (5-10 mg/l).
In the second water sample from the village of Tukaevo, there is a slight turbidity that appears immediately (10-100 mg/l).
In both water samples, the allowable rate of sulfate ions.
5. Iron detection
The maximum allowable concentration of total iron in water is 0.3 mg/l.
10 ml of the studied water samples from the city of Tarko-Sale and the village of Tukaevo were placed in a test tube, 1 drop of concentrated nitric acid, a few drops of hydrogen peroxide solution and approximately 0.5 ml of potassium thiocyanate solution were added. At a content of 0.1 mg / l, a pink color appears, and at a higher one, red.
When analyzing drinking water from the village of Tukaevo, there was no pink coloration, which means the concentration is less than 0.1 mg / l, which corresponds to the permissible norm of iron in water, and the water from Tarko-Sale turned red, which means the amount of iron in water is higher than MPC.
6. Detection of calcium ions
To determine the presence of calcium ions in the water of the city of Tarko-Sale and the village of Tukaevo, we used carbon dioxide, which was passed through the water. As a result of the experiment, the water of the city of Tarko-Sale did not change, and when passing through the water of the village of Tukaevo, a precipitate of calcium carbonate formed.
Conclusion: According to SanPiN, the calcium content in drinking water is not standardized, but by its amount we judge the hardness of water, which means that there is a small amount of calcium in the water of the city of Tarko-Sale, and a large amount in the water of the village of Tukaevo.
Conclusions and forecasts
When conducting organoleptic studies of water, the following indicators were obtained:
Water

Color (colour) colorless colorless
Transparency 10 cm 10 cm
Smell None (0) None (0)
Conclusion: Drinking water from the village of Tukaevo and the city of Tarko-Sale from the water supply system is suitable for drinking

When conducting a chemical analysis of water, the following indicators were obtained:
Water
Indicators Drinking water in the village of Tukaevo Drinking water in the city of Tarko-Sale
pH Neutral Alkaline
chlorides
White voluminous sediment (more than 100 mg/l) Slight turbidity (1-10 mg/l)

sulfates
Weak haze that appears immediately (10-100 mg/l) Weak haze that does not appear immediately (5-10 mg/l)
Iron cations No pink color, meaning less than 0.1 mg/l Red color, more than 0.3 mg/l
Calcium cations detected Not detected
According to the chemical analysis, tap water is suitable for drinking.

Literature
1. Scientific and methodological journal "Chemistry at School", No. 3, 2004
2. Gabrielyan O.S. "Chemistry grade 9", Textbook for general education. institutions. - 7th ed., Bustard, 2003.
3. Vasil'eva Z.G., Granovskaya A.A., Taperova A.A. "Laboratory work in general and inorganic chemistry", L .: Chemistry, 1986
4. Drinking water. State standards. Analysis methods. M: IPK.
Standards Publishing House, 1996. - /// p.
5. Handbook on the properties, methods of analysis and purification of H2O - part I. Ed. A.T. Pilipenko. Kiev: Naukova Dumka, 1980