STATE STANDARD OF THE UNION OF THE SSR

Introduction date 01.01.74

This standard applies to drinking water and establishes a complexometric method for determining the total hardness. The method is based on the formation of a strong complex compound of Trilon B with calcium and magnesium ions. The determination is carried out by titrating the sample with Trilon B at pH 10 in the presence of an indicator.

1. SAMPLING METHODS

2. EQUIPMENT, MATERIALS AND REAGENTS

3. PREPARATION FOR ANALYSIS

Where v is the amount of Trilon B solution used for titration, cm3.

4. CONDUCTING THE ANALYSIS

5. PROCESSING THE RESULTS

,

Where v is the amount of Trilon B solution used for titration, cm 3; K - correction factor to the normality of the Trilon B solution; V is the volume of water taken for determination, cm 3 . The discrepancy between repeated determinations should not exceed 2 rel. %. (Changed edition, Rev. No. 1).

INFORMATION DATA

Determination of water hardness in modern world- This required condition to ensure the performance of all equipment working with it. Nevertheless, it cannot be said that such a liquid is really harmful to humans. Everything should be in moderation, because excessively soft water causes no less damage to health than hard water.

The concept of water hardness

You should always start from the very basics, so that there is a complete understanding of the problem. In our case, before proceeding with the determination of water hardness, you first need to understand what it is. According to the results of an examination conducted in 2011 at the Department of Chemistry and Ecology of the Novgorod University named after. Yaroslav the Wise, for natural natural water, hardness is absolutely normal. Until the advent of modern technology, this question was of little interest to anyone; for thousands of years, people calmly used it in the form in which it is. Magnesium and calcium salts dissolved in water give hardness. The very concept of hardness arose as a result of the sensations of people, since when water saturated with these salts and other elements interacts with soap, foam practically does not form, making it difficult to wash or wash.

Types of stiffness

Before understanding what kind of water to drink, one should take into account the fact that hardness is not a homogeneous quantity. There are at least two:

• Temporary.
• Constant.

These types depend on the type of dissolved salts, which are always present in any hard water together, making up the total hardness. However, they can and should be separated. Temporary hardness directly depends on the presence of bicarbonate and hydrocarbonate anions. Their main feature is decomposition during boiling. As a result of the decomposition, water itself, carbon dioxide and calcium carbonate are obtained directly, which is practically insoluble. It turns out that you can get rid of temporary stiffness without any problems by simply raising the water temperature to +100 degrees. An example is any kettle. After prolonged use, a precipitate can be found inside, which is the result of the decomposition process described above. Everything that does not decompose in this way refers to permanent hardness, which is almost impossible to get rid of without special treatment.

Why you need to know the hardness of water

This is necessary in order to understand what kind of water you can drink safely, and also so that any equipment that interacts with water does not fail. For a person, excessively hard water is harmful. But even if this parameter is at an acceptable level for our body, the equipment will still not suit it. Aquariums, coffee, washing and dishwashers, kettles, multicookers and many other equipment options require water of a strictly defined hardness. Usually filters such as Geyser-3 help to cope with this, but often such a measure can even be considered unnecessary. Before spending money on them, it is recommended that you first test for water hardness, because it is quite possible that this indicator is already at a normal level.

Harm of hard and soft water

As mentioned above, first of all, it is not a certain type of water that causes damage to a person, but a complete lack of balance in the body.

Effects of hard water:

• Poor dissolution of foods (associated with Ca 2 + and Mg 2 + cations).
• Coffee, tea and any other similar drinks are brewed very poorly.
• With prolonged use, relaxation of the stomach is possible.
• Hard water can cause kidney stones to form.
• Saturates the body with the elements it needs.
• Improves the condition of the teeth, reduces the likelihood of caries.
• Hard water is the cause of the breakdown of most types of equipment.

Effects of soft water:

• Removes toxins, but along the way washes away useful elements (potassium, magnesium and calcium). As a result, the bones become more fragile. Also not in the best way affects the cardiovascular system.
• Negatively affects the pituitary-adrenal system.
• It has a bad effect on the water-salt balance of the body.

Thus, the determination of water hardness should not be done in order to get rid of it, but in order to minimize the negative impact and bring the use of such a liquid to the balance required by the body.

Sampling rules according to GOST

According to GOST, drinking water must be tested for hardness strictly in the laboratory, by means of titrimetric analysis. To do this, you first need to take samples, the volume of which must be at least 400 cubic centimeters (0.4 liters). As a container in which storage will be carried out, any container can be used if it is made of glass or polymeric material. It is very important to carry out the analysis no later than 24 hours after sampling. In special cases, when it is necessary to increase this period, the liquid is acidified by adding hydrochloric acid. In this state, it can be stored for about 1 month.

Titrimetric (laboratory) analysis

Among all water hardness, this option is deservedly considered the most reliable and complex. It is based on the process of formation of Trilon compounds together with alkaline earth ions. The minimum hardness index that can be determined using this method is 0.1 o F (7-10 o F is considered the norm). Ordinary tap water can be used as a sample. The best way out in a situation with suspected increased stiffness is to immediately visit the appropriate laboratory, since no home methods can give accurate data. But about them - below.

It makes no sense to fully describe the whole process, since it is impossible to reproduce it on your own, without the necessary skills and chemical elements and equipment. Nevertheless, there are several basic principles of reaction that remain in any situation and are inherent in absolutely all options:

• There must always be a way to fix the equivalence of the reaction, which is the basis for determining the stiffness.
• The analysis is carried out very quickly.
• The requirement of stoichiometric process must be met. Simply put, this means that no side products should form during the reaction.
• Once a reaction has begun, it cannot be reversed or stopped.

test strips

To determine the hardness of water at home, you can use special devices, which will not be difficult to buy (they are not prohibited and publicly available). They look like standard test strips. To use, it is enough to immerse one of them in the water that needs to be checked for the period of time specified in the instructions. As a result, the product will change its color. When using such strips to determine the hardness of water, the main problem is to determine what exactly the hardness indicator is. To do this, you need to compare the color on the strip and the examples with the description on the package. Unfortunately, it is far from always possible to immediately understand what exactly the device shows, and even in a clearer situation, the accuracy of the data leaves much to be desired. In general, such test strips are only suitable for a general understanding of how hard or soft water is.

home analysis

You can also check tap water for hardness using improvised means. True, this is more entertaining than really an option for testing fluid readings.

You need to take:

• A jar with a capacity of 1 liter (or any other similar capacity).
• A glass in the form of a cylinder.
• Any scales (it is most convenient to use electronic).
• Ruler.
• Laundry soap (72% or 60%).
• distilled water.

To check, you need to take 1 gram of soap, grind it and place it in a glass. After that, distilled water should be heated, but not brought to a boil. It should be poured into the glass in which the soap already lies. As a result, it must dissolve in water. The next step is to pour even more water. After that, pour into a jar of ordinary tap water and slowly pour the soapy liquid from the glass and mix (slowly). If foam is formed, then this is an indicator of stiffness. Unfortunately, it is almost impossible to say more or less clearly what exactly its level is using this method.

TDS analysis

Another option for determining the hardness of drinking water is to use a special device - a TDS meter. In principle, it is intended to determine what is affected both directly by salts (creating hardness) and many other elements, which does not give the desired level of accuracy. Moreover, the instrument readings a common person Those who do not know how to read them will not understand and are likely to get confused. Let's try to simplify the task. The vast majority of such devices use some ppm as units of measurement. We also use other options based on the equivalent of a milligram per liter of liquid. On average, 1 our unit (mg-eq / l) is equal to 50.05 foreign ppm. According to the rules, the concentration of salts (i.e. hardness) should be no more than 350 ppm or 7 mg-eq / l. These numbers are worth looking into. If the device is domestic, everything is greatly facilitated. Worst of all, when such a device is made somewhere in China or another similar country, which uses its own units of measurement. Then you will have to independently look for their equivalent and translate it into the testimony we are used to.

AKMS-1

Of the other devices capable of determining the hardness of water, the unique AKMS-1 device should be noted separately. This is a fairly large stationary unit, similar in size to the Geyser-3 filters. Just like that, at home, it is not possible to check the liquid with it. That is why such devices are used primarily in production, where water hardness can affect the operation of expensive equipment or cause other similar harm. Unlike all other analogues, AKMS-1 really quickly and accurately shows the current level of rigidity, allowing the operator to respond in a timely manner. With the help of this device, you can either let water go directly to the working units, if it does not pose a threat to them, or pre-filter it. This, of course, will result in additional costs, but it will help save on the repair of equipment, which will cost much more.

Results

Given all of the above and the requirements of GOST, drinking water should be regularly checked for hardness levels. Nevertheless, it is not worth taking radical measures to soften it, since both conditions are harmful - too hard and too soft. Only in the situation when the indicators are really higher or lower, it is worth taking some action. By the way, if hardness is regularly fought, then it is almost unheard of about too soft water, but you also need to pay no less attention to this.

All documents presented in the catalog are not their official publication and are intended for informational purposes only. Electronic copies of these documents can be distributed without any restrictions. You can post information from this site on any other site.

Foreword

Goals and principles of standardization in Russian Federation established by the Federal Law of December 27, 2002 No. 184-FZ "On Technical Regulation", and the rules for the application of national standards of the Russian Federation - GOST R 1.0-2004 "Standardization in the Russian Federation. Basic Provisions»

About the standard

1 DEVELOPED AND INTRODUCED by the Technical Committee for Standardization TC 343 "Water Quality" (SUE Center for Research and Water Control, FSUE VSEGINGEO, FSUE VNIIstandart, OOO Protector)

2 APPROVED AND INTRODUCED BY Order No. 317-st of December 20, 2005 of the Federal Agency for Technical Regulation and Metrology

3 This standard takes into account the main normative provisions of the following international ISO standards:

ISO 6059-1984 “Water quality. Determination of the total content of calcium and magnesium. Titrimetric method using EDTA" ( ISO 6059-1984 "Water quality - Determination of the sum of calcium and magnesium - EDTA titrimetric method" » (section 4 of this standard);

ISO 7980-1986 “Water quality. Determination of calcium and magnesium. Atomic absorption spectrometric method" ( ISO 7980-1986 Water quality - Determination of calcium and magnesium - Atomic absorption spectrometric method "") (clause 5.1 of this standard);

ISO 11885-1996 “Water quality. Determination of 33 elements by atomic emission with inductively coupled plasma” ( ISO 11885-1996 "Water quality - Determination of 33 elements by inductively coupled plasma atomic emission spectroscopy" "") (clause 5.2 of this standard)

4 INTRODUCED FOR THE FIRST TIME

Information about changes to this standard is published in the annually published information index "National Standards", and the text of changes and amendments - in the monthly published information indexes "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the monthly published information index "National Standards". Relevant information, notification and texts are also placed in information system general use - on the official website of the national body of the Russian Federation for standardization on the Internet

Introduction

Water hardness is one of the main indicators characterizing the use of water in various industries.

Water hardness is a set of properties determined by the content of alkaline earth elements in it, mainly calcium and magnesium ions.

Depending on the pH and alkalinity of the water, hardness above 10°H can cause sludge in the water distribution system and scale when heated. Water with a hardness of less than 5°H can be corrosive to water pipes. The hardness of water can also affect the applicability for human consumption in terms of its taste properties.

In the complexometric (titrimetric) determination of hardness, aluminum, cadmium, lead, iron, cobalt, copper, manganese, tin and zinc ions affect the establishment of the equivalent point and interfere with the determination. Orthophosphate and carbonate ions can precipitate calcium under titration conditions. The definition may also be hindered by some organic matter. If the interfering influence cannot be eliminated, it is recommended to determine the hardness using atomic spectrometry methods.

This standard provides for the use of various methods for determining water hardness, taking into account bringing the quantitative characteristics of water hardness (hardness units) in accordance with GOST R 52029.

Introduction date - 2007-01-01

1 area of ​​use

This standard applies to drinking and natural waters, including water sources of drinking water supply, and establishes the following methods for determining the hardness of water:

Complexometric method (method A);

Methods of atomic spectrometry (methods B and C).

Method B according to 5.1 is used to determine mass concentration calcium and magnesium ions.

Method B of 5.2 is an arbiter of other stiffness methods.

2 Normative references

This standard uses Normative references to the following standards:

In a conical flask with a capacity of 250 cm 3, add 10.0 cm 3 of a solution of magnesium ions (see), add 90 cm 3 of bidistilled water, 5 cm 3 of a buffer solution (see), from 5 to 7 drops of an indicator solution (see) or from 0.05 to 0.1 g of the dry mixture of the indicator (see) and immediately titrated with a solution of Trilon B (see) until the color changes at the equivalent point from wine-red (red-violet) to blue (with a greenish tint) when using indicator eriochrome black T, and when using the indicator chrome dark blue acid to blue (blue-violet).

A solution of Trilon B at the beginning of the titration is added quite quickly with constant stirring. Then, when the color of the solution begins to change, the Trilon B solution is added slowly. The equivalent point is reached when the color changes, when the color of the solution stops changing when drops of Trilon B solution are added.

Titration is carried out against the background of a titrated control sample. A slightly overtitrated test sample can be used as a control sample. The result is taken as the arithmetic mean of the results of at least two determinations.

Correction factor To to the concentration of Trilon B solution is calculated by the formula

,(1)

where V- volume of Trilon B solution used for titration, cm3;

10 - the volume of a solution of magnesium ions (see), cm 3.

Note - When preparing solutions according to 4.3, 4.4, it is allowed to use distilled water instead of bidistilled water if the determined hardness value is more than 1°L.

If the actual (reference) value of the stiffness in the reference sample is known, then the results are considered consistent provided that

|F L1- F L 2 | ≤ Rµ (5)

where F L1, F L2 - measurement results obtained in two laboratories, ° W;

R µ - reproducibility limit for the stiffness value µ ();

µ is the actual (reference) value of stiffness in the reference sample, °F.

Note - If in the GRMs used, the hardness is expressed in mmol / dm 3 (mol / m 3), then it is necessary to recalculate into degrees of hardness according toGOST R 52029 1)

1) The value of water hardness, expressed in mmol / dm 3, is numerically equal to the value expressed in ° F.

In accordance with the manual (instruction) for the operation of the spectrometer, calibration solutions are sprayed into the burner flame and the absorption of each element is recorded at the analytical wavelength. In the intervals between calibration solutions, it is recommended to introduce a hydrochloric acid solution. The calibration dependences of the absorption of calcium and magnesium on their content in the calibration solutions are established by the arithmetic mean of the results of three measurements for each calibration solution minus the arithmetic mean of the result of three measurements of the blank solution.

5.1.4.3 Control of the stability of the calibration dependencies is carried out every ten samples, repeating the measurement of one of the calibration solutions. If the measured concentration of this calibration solution differs from the actual one by more than 7%, then the calibration is repeated.

5.1.5 Sample preparation for analysis

In volumetric flasks with a capacity of 100 cm 3 add 10 cm 3 of a solution of lanthanum chloride if an air-acetylene flame is used, or 10 cm 3 of a solution of cesium chloride if a nitrous oxide-acetylene flame is used, then add an aliquot of the water sample (usually not more than 10 cm 3) and dilute to the mark with hydrochloric acid (see).

If the measured content of calcium or magnesium in the test sample is higher than the maximum values ​​established during the calibration of the spectrometer, then a reduced volume of the analyzed sample is used for determinations.

Note - When preparing solutions according to - 5.1.5, it is allowed to use volumetric flasks of smaller capacity, proportionally reducing the volumes of solutions and aliquots used.

5.1.6 Determination procedure

5.1.6.1 In accordance with the manual (instruction) for the operation of the spectrometer, the analyzed solutions are introduced into it, prepared according to , and in the intervals between them, a solution of hydrochloric acid (see ). Determine the absorption of each element at the analytical wavelength.

5.1.6.2 At the same time, conduct a blank test using the same reagents and in the same quantities as in the preparation of samples according to 5.1.5, replacing the test volume of the test sample with bidistilled water.

Note - When preparing solutions according to - 5.1.6, instead of a hydrochloric acid solution, it is allowed to use a solution of nitric acid with a molar concentration of 0.1 mol / dm 3.

5.1.7 Handling determination results

According to the calibration dependence (see), including using software spectrometer, determine the mass concentrations of calcium and magnesium in the test solutions and in the blank solution, and calculate the content of calcium and magnesium in the sample, taking into account the dilution of the sample and the value obtained in the experiment with the blank solution.

Hardness of water F, ° W, calculated by the formula

F = ∑(With i / With i e )· F· V to / V p ,(7)

where With i , - mass concentration of the element in the water sample, determined by the calibration dependence, minus the result of the analysis of the blank solution, mg/dm 3 ;

With i e - mass concentration of the element, mg / dm 3, numerically equal to its 1/2 mole;

F - dilution factor of the initial water sample during conservation (usuallyF = 1);

V to - the capacity of the flask in which the sample was prepared, by , cm 3;

V P - volume of water sample taken for analysis, cm 3 .

5.1.8 Metrological characteristics

The method ensures obtaining the results of measurements of elements (calcium and magnesium) with metrological characteristics not exceeding the values ​​given in Table 3, with a confidence level R= 0,95.

Table 3

5.1.9 Quality control of the results of determinations - according to. Instead of the GRM of the composition of water hardness, it is possible to use the GRM of the composition of aqueous solutions of magnesium and calcium ions. The repeatability and reproducibility limits are in accordance with Table 3.

5.1.10 Registration of results - according to. Meaning Δ calculated according to the formula

,(8)

where Δ e - the boundaries of the interval in which the measurement error of the element in the water sample is with a confidence probability R\u003d 0.95, mg / dm 3 (see table 3);

With i e - mass concentration of the element, mg / dm 3, numerically equal to its 1/2 mole.

Note - If it is necessary to calculate the hardness of water, taking into account the content of other alkaline earth elements, the determination of strontium ions is carried out according to GOST 23950, barium - according to GOST R 51309 , calculation and presentation of results - according to 5.2.

5.2 Determination of water hardness by measuring the concentrations of alkaline earth ions by inductively coupled plasma atomic emission spectrometry (method B)

5.2.1 Determination of the content of alkaline earth ions (magnesium, calcium, strontium, barium) in a water sample is carried out according to GOST R 51309.

Hardness of water F, ° W, calculated by the formula

F= ∑(С i /С i e ),(9)

where With i

With i e - mass concentration of the element, mg / dm 3, numerically equal to 1/2 of its mole.

5.2.2 Quality control of measurement results - according to . In this case, instead of the GRM of the composition of water hardness, it is possible to use the GRM of the composition of aqueous solutions of magnesium, calcium, barium, strontium ions; the values ​​of the limits of repeatability (convergence) and reproducibility - according to GOST R 51309 (table 4).

5.2.3 Registration of results - according to. Meaning Δ calculated according to the formula

,(10)

where δ - the boundaries of the interval in which the relative error in determining the element is with a confidence probability R\u003d 0.95 according to GOST R 51309 (table 3),%;

With i - mass concentration of the element in the water sample, determined according to GOST R 51309, mg / dm 3;

C i e - mass concentration of the element, mg / dm 3, numerically equal to its 1/2 mole.

5.2.4 If the concentration of strontium and barium ions in the water sample is less than 10% (in total) of the total content of alkaline earth elements, it is allowed not to take into account the content of strontium and barium when calculating water hardness.

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1 GOST Drinking water. Methods for determining the rigidity Group H09 Interstate standard Date of introduction Foreword The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST "Interstate standardization system. Basic provisions" and GOST "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Rules development, adoption, application, updating and cancellation" Information about the standard 1 PREPARED by the Society with limited liability Protector together with Closed joint stock company"Water Research and Control Center" 2 INTRODUCED by the Federal Agency for Technical Regulation and Metrology (Rosstandart) 3 ACCEPTED by the Interstate Council for Standardization, Metrology and Certification (by correspondence, protocol dated December 3, 2012 N 54) Voted for the adoption of the standard: Short name countries according to MK (ISO 3166) Country code according to MK (ISO 3166) Abbreviated name of the national standardization body Armenia AM Ministry of Economy of the Republic of Armenia Belarus BY Gosstandart of the Republic of Belarus Kazakhstan KZ Gosstandart of the Republic of Kazakhstan Kyrgyzstan KG Kyrgyzstandart Moldova MD Moldova-Standard Russian Federation RU Rosstandart Tajikistan TJ Tajikstandart Uzbekistan UZ Uzstandart 4 This standard takes into account the main regulatory provisions of international ISO standards 6059:1984 Water quality - Determination of the sum of calcium and magnesium - EDTA titrimetric method, ISO 7980:1986 Water quality - Determination of calcium and magnesium - Atomic absorption spectrometric method (Water quality. Determination of calcium and magnesium. Atomic absorption spectrometric

2 method). Degree of conformity - non-equivalent (NEQ) The standard was prepared on the basis of the application of GOST R By order of the Federal Agency for Technical Regulation and Metrology dated December 12, 2012 N 1899-st, the interstate standard was put into effect as the national standard of the Russian Federation from January 1, 2014. 6 INTRODUCED FOR THE FIRST TIME Information about changes to this standard is published in the annually published information index "National Standards", and the text of changes and amendments - in the monthly published information index "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the monthly published information index "National Standards". Relevant information, notification and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet Introduction Water hardness is one of the main indicators characterizing the use of water in various industries. Water hardness is a set of properties determined by the content of alkaline earth elements in it, mainly calcium and magnesium ions. Depending on the pH and alkalinity of the water, a hardness above 10 F may cause the formation of slag in the water distribution system and scale when heated. Water with a hardness of less than 5 F can be corrosive to water pipes. The hardness of water can also affect the applicability for human consumption in terms of its taste properties. In the complexometric (titrimetric) determination of hardness, aluminum, cadmium, lead, iron, cobalt, copper, manganese, tin and zinc ions affect the establishment of the equivalent point and interfere with the determination. Orthophosphate and carbonate ions can precipitate calcium under titration conditions. Certain organic substances may also interfere with the determination. If the interfering influence cannot be eliminated, it is recommended to determine the hardness using atomic spectrometry methods. This standard provides for the use of various methods for determining water hardness, taking into account the quantification of water hardness (hardness units) through degrees of hardness (H) according to GOST Scope This standard applies to natural (surface and ground) waters, including drinking water sources, as well as drinking water, including packaged in containers, and establishes the following methods for determining

3 including those packaged in containers, and establishes the following methods for determining water hardness: - complexometric method (method A); - methods of atomic spectrometry (methods B and C). Method B is used to determine the mass concentration of calcium and magnesium ions. Method B is an arbitrage in relation to other methods for determining the stiffness. 2 Normative references This standard uses normative references to the following interstate standards: GOST Nature Protection. Hydrosphere. General requirements for sampling of surface and sea waters, ice and atmospheric precipitation GOST (ISO , ISO) Measuring laboratory glassware. Cylinders, beakers, flasks, test tubes. Specifications GOST Reagents. Sodium sulphide 9-water. Specifications GOST Reagents. Hydrochloric acid. Specifications GOST Reagents. Ammonia water. Specifications GOST Reagents. Ammonium chloride. Specifications GOST Reagents. Sodium chloride. Specifications GOST Reagents. sodium hydroxide. Specifications GOST Reagents. Nitric acid. Specifications GOST Reagents. Hydroxylamine hydrochloride. Specifications GOST Technical dissolved and gaseous acetylene. Specifications GOST Distilled water. Specifications GOST Reagents. Disodium salt of ethylenediamine-n,n,n,n-tetraacetic acid 2-aqueous (trilon B). Specifications GOST ISO/IEC General requirements for the competence of testing and calibration laboratories GOST Industrial purity. Compressed air. Contamination classes GOST Rectified technical ethyl alcohol. Specifications GOST Drinking water. Method for determining the mass concentration of strontium GOST Laboratory glassware and equipment. Types, basic

4 parameters and dimensions GOST (ISO) Laboratory glassware. Pipettes with one mark GOST (ISO) Laboratory glassware. Pipettes graduated. Part 1. General requirements GOST (ISO) Laboratory glassware. Burettes. Part 1. General requirements GOST Water. General requirements for sampling GOST Drinking water. Sampling GOST Water. GOST hardness unit Drinking water. Determination of the content of elements by atomic spectrometry as of January 1 of the current year, and according to the corresponding monthly published information indexes published in the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replacing (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected. 3 Sampling General requirements for sampling - in accordance with GOST 31861, GOST and GOST polymer materials or glass. The shelf life of a water sample is no more than 24 hours. To increase the shelf life of the sample and to prevent precipitation of calcium carbonates from water (which is typical for groundwater or bottled water), the sample is acidified with acid to pH<2. При определении жесткости по методу А подкисление проводят соляной кислотой, по методу Б - соляной или азотной кислотой, при использовании метода В - азотной кислотой. Контроль рн проводят по универсальной индикаторной бумаге или с использованием рн-метра. Срок хранения подкисленной пробы воды - не более 1 мес. Для воды, расфасованной в емкости, сроки и температурные условия хранения должны соответствовать требованиям, указанным в нормативной документации* на готовую продукцию.

5 * In the Russian Federation - to the requirements of GOST R "Drinking water packaged in containers. General technical conditions" - is re-registered as an interstate standard. 4 Complexometric method (method A) 4.1 Essence of the method The method is based on the formation of complex compounds of Trilon B with ions of alkaline earth elements. The determination is carried out by titrating the sample with a solution of Trilon B at pH=10 in the presence of an indicator. The lowest determined water hardness is 0.1 W. If the test sample was acidified for preservation or the sample has an acidic environment, then sodium hydroxide solution (cm) is added to an aliquot of the sample to pH = 6-7. If the water sample has a strongly alkaline environment, then a hydrochloric acid solution (cm) is added to the sample aliquot to pH = 6-7. pH control is carried out using universal indicator paper or using a pH meter. To remove carbonate and bicarbonate ions from water (which is typical for underground or bottled waters), after adding hydrochloric acid to an aliquot of a sample of a solution of hydrochloric acid to pH = 6-7, it is boiled or blown with air or any inert gas for at least five minutes to remove carbon dioxide gas. The alkaline reaction of water can serve as a criterion for the presence of a significant amount of carbonates in water. Presence in water of more than 10 mg/dm3 of iron ions; more than 0.05 mg / dm3 of each of the ions of copper, cadmium, cobalt, lead; more than 0.1 mg / dm3 of each of the ions of manganese (II), aluminum, zinc, cobalt, nickel, tin, as well as a color of more than 200 F and increased turbidity cause a fuzzy color change at the equivalence point during titration and lead to an overestimation of the results of determining hardness . Orthophosphate and carbonate ions can precipitate calcium under titration conditions at pH=10. To reduce the effect of zinc contained in water up to 200 mg/dm, aluminum, cadmium, lead up to 20 mg/dm, iron up to 5 mg/dm, manganese, cobalt, copper, nickel up to 1 mg/dm, add to the sample aliquot before introducing the indicator 2 ml of sodium sulfide solution (cm); to reduce the effect of manganese to 1 mg/dm, iron, aluminum to 20 mg/dm, copper to 0.3 mg/dm add 5 to 10 drops of hydroxylamine hydrochloride solution (cm). Turbidity (suspended matter) of the sample is eliminated by filtration through membrane filters with a pore diameter of 0.45 µm or blue tape ashless paper filters. The influence of color and other factors is eliminated by diluting the sample during the analysis according to 4.5, if the determined value of water hardness allows this. NOTE Filtration of the sample may lead to an underestimation of the hardness of the water, especially alkaline water. If interfering influences cannot be eliminated, then the determination of stiffness is carried out

6 methods of atomic spectrometry. 4.2 Measuring instruments, auxiliary equipment, reagents, materials State (interstate) standard sample (GSO) of the composition of hardness (total hardness) of water with a relative error of the certified value at a confidence level of 0.95, not more than ±1.5%. Laboratory scales* with a maximum weighing limit of 220 g, ensuring weighing accuracy with a maximum permissible absolute error limit of ±0.75 mg. * GOST R "Non-automatic scales. Part 1. Metrological and technical requirements. Tests" is in force in the Russian Federation. pH meter of any type. Volumetric flasks according to GOST of the first accuracy class. Pipettes graduated according to GOST accuracy class or pipettes with one mark according to GOST accuracy class. Burettes according to GOST of the first accuracy class with a capacity of 25 cm and (or) 10 cm. Measuring cylinders (beakers) according to GOST Flat-bottomed or conical flasks according to GOST Dropper 2-50 XC according to GOST Laboratory funnels according to GOST Chemical heat-resistant glasses according to GOST Device for filtering samples with using membrane filters. Membrane filters with a pore diameter of 0.45 µm or deashed paper "blue tape". Cabinet drying laboratory, maintaining the temperature (80 ± 5) C. Universal indicator paper for pH control. Distilled water according to GOST 6709 and (or) bidistilled water (distilled water, re-distilled in glass containers). GSO composition of Trilon B with a mass fraction of 2-aqueous disodium salt of ethylenediamine-N,N,N,N-tetraacetic acid, not less than 99.5% or standard titer (fixanal) of Trilon B or Trilon B (ethylenediamine-n,n,n, n-tetraacetic acid disodium salt 2-aqueous) according to GOST 10652, analytical grade. or h.h. GSO of the composition of an aqueous solution of magnesium ions with a relative error

7 certified value at a confidence level standard titer (fixanal) sulfate (sulphate) magnesium. 0.95 no more than ±1.0% or Standard titer (fixanal) of hydrochloric acid or nitric acid with a molar concentration of 0.1 mol/dm. Rectified ethyl alcohol in accordance with GOST Indicator eriochrome black T (chromogenic black ET) or chromic dark blue acid (acid chromic blue T). Ammonium chloride according to GOST 3773, analytical grade Water ammonia according to GOST 3760 (25%), chemically pure Hydrochloric acid according to GOST 3118, chemically pure, or nitric acid according to GOST 4461, chemically pure. Sodium hydroxide according to GOST 4328, chemically pure Sodium chloride according to GOST 4233, chemically pure Sodium sulfide according to GOST 2053, analytical grade Hydroxylamine hydrochloride according to GOST 5456, analytical grade. or h.h. Note - It is allowed to use other measuring instruments, equipment and reagents, including imported ones, with technical and metrological characteristics not worse than those indicated. 4.3 Preparation of solutions and indicators A solution of Trilon B with a molar concentration of 25 mmol / dm Trilon B is dried at 80 C for two hours, weighed 9.31 g, placed in a volumetric flask with a capacity of 1000 ml, dissolved in warm bidistilled water from 40 C to 60 C and after cooling the solution to room temperature, dilute to the mark with bidistilled water. The adjustment factor for the concentration of the Trilon B solution (see 4.4), prepared from a sample, is set according to the magnesium sulfate solution (cm). A solution from the GSO composition of Trilon B or the standard titer (fixanal) of Trilon B is prepared in accordance with the instructions for use, diluting it to the required concentration. Trilon B solution is suitable for use within 6 months. It is recommended to check the value of the correction factor at least once a month. Magnesium ion solution with a molar concentration of 25 mmol/dm. necessary diluting to the required concentration. Note - If in the used standard titers (fixed channels) or GSO of the composition

8 aqueous solutions, the concentration of a substance is expressed in normalities (n), mg/dm, g/m, etc., it is necessary to recalculate the concentration of a substance in mol/dm Buffer solution pH=(10±0.1) 10 g of ammonium chloride is placed in a volumetric flask with a capacity of 500 cm3, 100 cm3 of bidistilled water is added to dissolve it and 50 cm3 of 25% aqueous ammonia, mixed thoroughly and brought to the mark with bidistilled water. The buffer solution is suitable for use for 2 months if stored in a tightly closed container made of polymeric material. It is recommended to periodically check the pH of the buffer solution using a pH meter before using it. If the pH value has changed by more than 0.2 pH units, then prepare a new buffer solution Indicators Indicator solution mix thoroughly and add 80 ml of ethyl alcohol. The solution is suitable for use within 10 days when stored in a dark glass container. Instead of the eriochrome black T indicator, it is allowed to use the chrome dark blue acid indicator, the solution of which is prepared in a similar way. The shelf life of this solution is not more than 3 months. Dry mixture of the indicator Dry mixture of the indicator is prepared in the following sequence: 0.25 g of black T eriochrome is mixed with 50 g of sodium chloride in a porcelain mortar and thoroughly ground. The mixture is suitable for use for one year when stored in a dark glass container Hydroxylamine hydrochloride solution To prepare 100 ml of a solution, 1 g of hydroxylamine hydrochloride () is dissolved in 100 ml of bidistilled water. The solution is suitable for use within 2 months. Sodium sulfide solution To prepare 100 ml of a solution, 5 g of sodium sulfide or 3.5 g is dissolved in 100 ml of bidistilled water. The solution is prepared on the day of the determination. A solution of hydrochloric acid with a molar concentration of 0.1 mol / dm

9 In a volumetric flask with a capacity of 1000 ml, half-filled with bidistilled water, pour 8 ml of hydrochloric acid and bring to the mark with bidistilled water. The shelf life of the solution is no more than 6 months. The preparation of an acid solution from a standard titer (fixanal) is carried out in accordance with the instructions for its preparation Sodium hydroxide solution with a molar concentration of 0.2 mol / dm To prepare 1000 ml of a solution, 8 g of sodium hydroxide is placed in a glass, dissolved in bidistilled water, after cooling the solution Transfer to a 1000 ml volumetric flask and dilute to the mark with bidistilled water. The shelf life of the solution in a container made of polymeric material is no more than 6 months. 4.4 Establishment of the correction factor for the concentration of Trilon B solution In a conical flask with a capacity of 250 ml, add 10.0 ml of magnesium ion solution (cm), add 90 ml of bidistilled water, 5 ml of buffer solution (cm), from 5 to 7 drops of indicator solution (cm ) or from 0.05 to 0.1 g of indicator dry mix (ml) and immediately titrate with Trilon B solution (ml) until the color changes at the equivalent point from wine-red (red-violet) to blue (with a greenish tinge) when using indicator eriochrome black T, and when using the indicator chrome dark blue acid to blue (blue violet). A solution of Trilon B at the beginning of the titration is added quite quickly with constant stirring. Then, when the color of the solution begins to change, the Trilon B solution is added slowly. The equivalent point is reached when the color changes, when the color of the solution ceases to change when drops of Trilon B solution are added. The titration is carried out against the background of a titrated control sample. A slightly overtitrated test sample can be used as a control sample. The result is taken as the arithmetic mean of the results of at least two determinations. The value of the correction factor should be equal to 1.00±0.03. The correction factor for the formula to the concentration of Trilon B solution is calculated by, (1) where is the volume of Trilon B solution used for titration, cm, 10 is the volume of magnesium ion solution (cm), see Note - When preparing solutions, it is allowed to use instead of bidistilled water distilled water, if the determined hardness value is more than 1 F.

10 4.5 Procedure for carrying out determinations Perform two determinations, for which the sample of the analyzed water is divided into two parts. In a flask with a capacity of 250 ml, place the first part of an aliquot of the sample of the analyzed water with a volume of 100 ml, 5 ml of a buffer solution (cm), from 5 to 7 drops of an indicator solution ( cm) or from 0.05 to 0.1 g of the indicator dry mix (cm) and titrated with a solution of Trilon B (cm) as described in the second part of the 100 ml aliquot of the sample is placed in a 250 ml flask, 5 ml of buffer solution is added, from 5 to 7 drops of indicator solution or from 0.05 to 0.1 g of dry indicator mixture, add Trilon B solution, which is taken 0.5 cm less than that used for the first titration (cm), mix quickly and thoroughly and titrate (titrate) as described in 4.4. NOTE 1 An indistinct change in color of the indicator at the equivalent point, or a change in color to gray, indicates the presence of interfering substances. Elimination of interfering influences - according to 4.1. If interfering influences cannot be eliminated, the determination of hardness is carried out by methods of atomic spectrometry (see Section 5). 2 If the consumption of Trilon B solution exceeds 20 cm3 - when using a burette with a capacity of 25 cm3 or 9 cm3 - when using a burette with a capacity of 10 cm3, then the volume of the analyzed sample is reduced by adding bidistilled water to it to a volume of 100 cm3. The sample aliquot is also reduced to eliminate the influence color of water. 3 If the consumption of Trilon B solution is less than 1 cm3 - when using a burette with a capacity of 25 cm3 or less than 0.5 cm3 - when using a burette with a capacity of 10 cm3, then it is recommended to use a Trilon B solution with a molar concentration of 5 mmol/dm3 or 2.5 mmol/dm3, respectively . Trilon B solution is diluted 5 or 10 times. 4.6 Processing the results of determination Water hardness, W, is calculated by the formula - dilution factor of the initial water sample during conservation (usually 1);

11 - correction factor to the concentration of Trilon B solution, calculated by formula (1); - volume of Trilon B solution used for titration, cm; - the volume of the water sample taken for analysis, cm The result of the measurement is the arithmetic mean of the results of two determinations. The acceptability of the results of the determinations is evaluated based on the condition: where is the repeatability limit (see Table 1);, (3) and are the results of the determinations according to and 4.5.3, G. If the discrepancy between the two results exceeds the specified value, then the determination of water hardness is repeated. In this case, the acceptance test is carried out according to . 4.7 Metrological characteristics The method provides measurement results with metrological characteristics not exceeding the values ​​given in Table 1, with a confidence level of 0.95. Table 1 Rigidity measurement range, W From 0.1 to 0.4 inclusive. Accuracy indicator (boundaries * of the interval in which the error is with a confidence probability of 0.95), F Repeatability limit, F Reproducibility limit, F 0.05 0.05 0.07 St. 0.4 0.15 0.1 0, 21 * The specified numerical values ​​of the limits of the interval for the error correspond to the numerical values ​​of the expanded uncertainty (in relative units) at a coverage factor of 2. The uncertainty assessment is carried out as indicated in . 4.8 Control of quality indicators of measurement results Control of quality indicators of measurement results in the laboratory involves monitoring the stability of measurement results taking into account the requirements or using GSO or GSO solution of the composition of water hardness, which most reflects the value of hardness of the waters analyzed in the laboratory. Note - If in the GRMs used, the hardness is expressed in mmol / dm (mol / m),

12 must be converted to degrees of hardness *. * The value of water hardness, expressed in mmol / dm, is numerically equal to the value expressed in G. 4.9 Presentation of results The measurement results are recorded in the protocol (report) in accordance with GOST ISO / IEC The protocol indicates the method used in the laboratory according to this standard. The measurement result can be presented as:, (6) where is the value of water hardness, F; - the boundaries of the interval in which the error in determining the hardness of water is with a confidence level of 0.95 (see table 1). 5 Methods of atomic spectrometry 5.1 Determination of water hardness by measuring the concentrations of calcium and magnesium ions by flame atomic absorption spectrometry (method B) in flames. To eliminate interfering influences, lanthanum chloride or cesium chloride is added to the sample aliquot Measuring instruments, auxiliary equipment, reagents, materials - according to 4.2 with the following additions: atomic absorption spectrometer, configured and installed in accordance with the operating manual (instruction), equipped for use an air-acetylene or nitrous oxide-acetylene flame, a hollow cathode lamp for the determination of calcium and magnesium. NOTE A nitrous oxide-acetylene flame is recommended if the composition of the samples is complex or unknown, and for samples with a high content of phosphates, sulfates, aluminum ions or silicon; GRM of the composition of aqueous solutions of magnesium ion and calcium ion with a relative error of certified values ​​of mass concentrations of not more than ±1% at a confidence level of 0.95; lanthanum chloride heptahydrate, or lanthanum oxide, chemically pure, if

13 use an air-acetylene flame, or cesium chloride use a nitrous oxide-acetylene flame;, h.ch., if nitrous oxide; compressed air according to GOST 17433; acetylene according to GOST Preparation of solutions Solution of lanthanum chloride, mass concentration of lanthanum 20 g / dm To prepare 1000 ml of a solution, 24 g of lanthanum oxide is slowly and carefully dissolved in 50 ml of concentrated hydrochloric acid, shaking until the lanthanum oxide is dissolved, the solution is transferred into a volumetric flask with a capacity of 1000 ml and dilute to the mark with bidistilled water or dissolve 54 g of lanthanum chloride in 500 to 600 ml of hydrochloric acid (cm), transfer to a 1000 ml volumetric flask and dilute to the mark with hydrochloric acid. Shelf life of the solution - no more than 3 months Cesium chloride solution, mass concentration of cesium 20 g / dm To prepare 1000 cm3 solution, 25 g of cesium chloride is placed in a volumetric flask with a capacity of 1000 cm3 and adjusted to the mark with a solution of hydrochloric acid (cm3). The shelf life of the solution is no more than 3 months. The main solution of calcium-magnesium To prepare the main solution of calcium-magnesium with a mass concentration of calcium 20 mg / dm3 and magnesium 4 mg / dm3, 20.0 cm3 of the composition of an aqueous solution of calcium is added with a pipette into a volumetric flask with a capacity of 1000 cm 3 mass concentration of 1 g / dm and 4.0 cm GSO of the composition of an aqueous solution of magnesium with a mass concentration of 1 g / dm and bring to the mark with a solution of hydrochloric acid (cm). It is allowed to prepare the basic solution of calcium-magnesium with other values ​​of the concentration of calcium and magnesium ions, which most reflect the composition of the analyzed waters. Shelf life of the solution - no more than 2 months Calibration solutions of calcium and magnesium In seven volumetric flasks with a capacity of 100 ml, add 10 ml of a solution of lanthanum chloride (cm) if an air-acetylene flame is used, or 10 ml of a solution of cesium chloride (cm) if a flame is used nitrous oxide-acetylene; then, the required volume of the basic solution of calcium-magnesium is added to six volumetric flasks (see table 2), it is not added to the seventh flask (blank solution). Dilute the contents of all seven flasks to the mark with hydrochloric acid (ml). The shelf life of the solution is no more than 1 month. Examples of obtained concentrations of calcium and magnesium calibration solutions

14 are given in Table 2. Table 2 Mass concentration, mg/dm Volume of the basic solution of calcium-magnesium, cm calcium ions 0 1.0 2.0 3.0 5, magnesium ions 0 0.2 0.4 0.6 1, 0 2.0 3, Preparing the spectrometer The atomic absorption spectrometer is prepared for operation in accordance with the operation manual (instruction). The values ​​of analytical wavelengths for calcium are 422.7 nm, for magnesium - 285.2 nm Calibration of the spectrometer In accordance with the manual (instruction) for the operation of the spectrometer, calibration solutions are sprayed into the burner flame and the absorption of each element is recorded at the analytical wavelength. In the intervals between calibration solutions, it is recommended to introduce a hydrochloric acid solution. The calibration dependences of the absorption of calcium and magnesium on their content in the calibration solutions are established by the arithmetic mean of the results of three measurements for each calibration solution minus the arithmetic mean of the result of three measurements of the blank solution. The stability of the calibration dependences is checked every ten samples, repeating the measurement of one of the calibration solutions. If the measured concentration of this calibration solution differs from the actual concentration by more than 7%, then the calibration is repeated Preparation of samples for analysis In volumetric flasks with a capacity of 100 ml add 10 ml of a solution of lanthanum chloride, if an air-acetylene flame is used, or 10 ml of a solution of cesium chloride, if a nitrous oxide-acetylene flame is used, then add an aliquot of the water sample (usually not more than 10 ml) and make up to the mark with hydrochloric acid (ml). If the measured content of calcium or magnesium in the test sample is higher than the maximum values ​​established during the calibration of the spectrometer, then a reduced volume of the analyzed sample is used for determinations. Notes 1 When preparing solutions according to 5.1.3, it is allowed to use volumetric flasks of smaller capacity, proportionally reducing the volumes of solutions and aliquots used. 2 When preparing solutions according to 5.1.3, 5.1.5, instead of a hydrochloric acid solution, it is allowed to use a nitric acid solution with a molar concentration of 0.1 mol/dm.

15 5.1.6 Procedure for carrying out the determination In accordance with the manual (instruction) for the operation of the spectrometer, the analyzed solutions are introduced into it, prepared according to, and in the intervals between them - a solution of hydrochloric acid (cm). Determine the absorption of each element at the analytical wavelength Simultaneously, a blank experiment is carried out using the same reagents and in the same quantities as in the preparation of samples according to 5.1.5, replacing the test volume of the analyzed sample with bidistilled water. including using the software of the spectrometer, they determine the mass concentrations of calcium and magnesium in the studied solutions and in the blank solution and calculate the content of calcium and magnesium in the sample, taking into account the dilution of the sample and the value obtained in the experiment with the blank solution. Water hardness, W, is calculated by the formula, (7) g de e - mass concentration of the element in the water sample, determined by the calibration dependence, minus the result of the analysis of the blank solution, mg / dm; - mass concentration of the element, mg/dm, numerically equal to its 1/2 mole; - dilution factor of the initial water sample during conservation (usually 1); - capacity of the flask in which the sample was prepared, according to 5.1.5, cm3; - volume of water sample taken for analysis, see Metrological characteristics The method ensures obtaining the results of measurements of elements (calcium and magnesium) with metrological characteristics not exceeding the values ​​given in Table 3, with a confidence level of 0.95. Table 3

16 Measurement range of element concentration, mg/dm From 1.0 to 50 inclusive. Accuracy indicator (boundaries* of the interval in which the measurement error is with a confidence probability of 0.95), mg/dm 0.07 0.1 * The established numerical values ​​of the limits of the interval for the error correspond to the numerical values ​​of the expanded uncertainty (in relative units) at a coverage factor of 2. The uncertainty assessment is carried out as indicated in Control of the quality indicators of the results of determinations - according to 4.8. In this case, instead of the GRM of the composition of water hardness, it is possible to use the GRM of the composition of aqueous solutions of magnesium and calcium ions. The values ​​of repeatability and reproducibility limits - in accordance with the table Formulation of results - according to 4.9. The value is calculated by the formula where, (8) - the boundaries of the interval in which the measurement error of the element in the water sample is with a confidence level of 0.95, mg/dm (see Table 3); - mass concentration of the element, mg/dm, numerically equal to its 1/2 mole. Note - If it is necessary to calculate the hardness of water, taking into account the content of other alkaline earth elements, the determination of strontium ions is carried out in accordance with GOST 23950, barium - in accordance with GOST 31870, while the hardness value is calculated according to formula (9), control of indicators - according to 5.2.2, presentation of results - according to Determination of water hardness by measuring the concentrations of alkaline earth ions by inductively coupled plasma atomic emission spectrometry (method B) Determination of the content of alkaline earth ions (magnesium, calcium, strontium, barium) in a water sample is carried out according to GOST formula, (9) where is the mass concentration of the element in the water sample, determined according to GOST 31870, mg/dm; - mass concentration of the element, mg/dm, numerically equal to 1/2 of its mole Control of quality indicators of measurement results - according to 4.8. Meanwhile, instead of

17 GSO for the composition of water hardness, you can use the GSO for the composition of aqueous solutions of magnesium, calcium, barium, strontium ions; values ​​of repeatability (convergence) and reproducibility limits - according to GOST (table 4) Presentation of results - according to 4.9. The value is calculated by the formula, (10) where - the boundaries of the interval in which the relative error in determining the element is with a confidence level of 0.95 according to GOST (see Table 3),%; ; - mass concentration of the element in the water sample, determined according to GOST 31870, mg/dm - mass concentration of the element, mg/dm, numerically equal to its 1/2 mole When the concentration of strontium and barium ions in the water sample is less than 10% (in total) of the total content alkaline earth elements, it is allowed not to take into account the content of strontium and barium when calculating the hardness of water. Bibliography Accuracy (trueness and precision) of measurement methods and results. International Part 6. Use in practice of accuracy values ​​(Accuracy (correctness and ISO standard precision) of measurement methods and results. Part: 1994* Use of accuracy values ​​in practice) and measurement results - Part 6: Use of accuracy values ​​in practice". Prior to the adoption of an interstate standard, similar national standards are used if they are identical to the international standard ISO: 1994. EUROCHEM/SITAC Manual "Quantifying Uncertainty in Analytical Measurements"*. 2nd edition, 2000, trans. from English. - St. Petersburg, VNIIM named after D.I. Mendeleev, 2002 * The document is not given. See the link for more information. - Database manufacturer's note. MI recommendation State system for ensuring the uniformity of measurements. Methods of quantitative chemical analysis. Procedures for checking the acceptability of the results of the analysis

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GOST 4151-72

STATE STANDARD OF THE UNION OF THE SSR

DRINKING WATER

Method for determining the total hardness

Method for determination

of total hardness content

Introduction date 01.01.74

This International Standard applies to drinking water and specifies a complexometric method for the determination of total hardness.

The method is based on the formation of a strong complex compound of Trilon B with calcium and magnesium ions.

The determination is carried out by titrating the sample with Trilon B at pH 10 in the presence of an indicator.

1. SAMPLING METHODS

1.1. Water samples are taken according to GOST 2874 and GOST 4979.

1.2. The volume of the water sample to determine the total hardness must be at least 250 cm 3 .

1.3. If the determination of hardness cannot be carried out on the day of sampling, then the measured volume of water, diluted 1:1 with distilled water, may be left for determination until the next day.

Water samples intended to determine the total hardness are not preserved.

2. EQUIPMENT, MATERIALS AND REAGENTS

Measured laboratory glassware according to GOST 1770 with a capacity of: pipettes 10, 25, 50 and 100 cm 3 without divisions; burette 25 cm3.

Flasks conical according to GOST 25336 with a capacity of 250-300 cm 3.

Dropper according to GOST 25336.

Trilon B (complexon III, disodium salt of ethylenediaminetetraacetic acid) according to GOST 10652.

Ammonium chloride according to GOST 3773.

Water ammonia according to GOST 3760, 25% solution.

Hydroxylamine hydrochloric acid according to GOST 5456.

Citric acid according to GOST 3118.

Sodium sulfide (sodium sulfide) according to GOST 2053.

Sodium chloride according to GOST 4233.

Rectified ethyl alcohol according to GOST 5962.

Zinc metal granulated.

Magnesium sulfate - fixanal.

Chromogen black special ET-00 (indicator).

Chrome dark blue acidic (indicator).

All reagents used for analysis must be of analytical grade (analytical grade)

3. PREPARATION FOR ANALYSIS

3.1. Distilled water, distilled twice in a glass apparatus, is used to dilute the water samples.

3.2. Preparation 0.05 n. Trilon B solution

9.31 g of Trilon B is dissolved in distilled water and adjusted to 1 dm 3 . If the solution is cloudy, then it is filtered. The solution is stable for several months.

3.3. Buffer solution preparation

10 g of ammonium chloride (NH 4 Cl) are dissolved in distilled water, 50 cm 3 of 25% ammonia solution are added and brought to 500 cm 3 with distilled water. To avoid loss of ammonia, the solution should be stored in a tightly closed bottle.

3.4. Preparation of indicators

0.5 g of the indicator is dissolved in 20 cm 3 of a buffer solution and adjusted to 100 cm 3 with ethyl alcohol. The dark blue chromium indicator solution can be stored for a long time without change. The black chromogen indicator solution is stable for 10 days. It is allowed to use a dry indicator. To do this, 0.25 g of the indicator is mixed with 50 g of dry sodium chloride, previously thoroughly ground in a mortar.

3.5. Preparation of sodium sulfide solution

5 g of sodium sulfide Na 2 SCH9H 2 O or 3.7 g of Na 2 SCH5H 2 O is dissolved in 100 cm 3 of distilled water. The solution is stored in a bottle with a rubber stopper.

3.6. Preparation of a solution of hydrochloric acid hydroxylamine

1 g of hydroxylamine hydrochloride NH 2 OHCHHCl is dissolved in distilled water and adjusted to 100 cm 3 .

3.7. Preparation of 0.1 n. zinc chloride solution

The exact weight of 3.269 g of granulated zinc is dissolved in 30 cm 3 of hydrochloric acid, diluted 1:1. Then bring the volume in a volumetric flask with distilled water to 1 dm 3 . Get the exact 0.1 N. solution. Dilution of this solution by half gives 0.05 N. solution. If the sample is inaccurate (more or less than 3.269), then calculate the number of cubic centimeters of the initial zinc solution to prepare an accurate 0.05 N. solution, which should contain 1.6345 g of zinc in 1 dm 3.

3.8. Preparation 0.05 n. magnesium sulfate solution

The solution is prepared from fixanal, attached to the set of reagents for determining the hardness of water and designed to prepare 1 dm 3 0.01 n solution. To obtain 0.05 n. solution, the contents of the ampoule are dissolved in distilled water and the volume of the solution in the volumetric flask is adjusted to 200 cm 3 .

3.9. Setting the correction factor for the normality of the Trilon B solution

In a conical flask contribute 10 cm 3 0.05 n. zinc chloride solution or 10 cm 3 0.05 n. magnesium sulfate solution and diluted with distilled water to 100 cm 3 . Add 5 cm 3 of the buffer solution, 5-7 drops of the indicator and titrate with strong shaking with a solution of Trilon B until the color changes at the equivalent point. The color should be blue with a violet tint when a dark blue chromium indicator is added and blue with a greenish tint when a black chromogen indicator is added.

Titration should be carried out against the background of a control sample, which may be a slightly overtitrated sample.

Correction factor ( To) to the normality of a solution of Trilon B is calculated by the formula

where v- the amount of Trilon B solution used for titration, cm 3 .

4. CONDUCTING THE ANALYSIS

4.1. The determination of the total hardness of water is hindered by: copper, zinc, manganese and a high content of carbonic and bicarbonate salts. The influence of interfering substances is eliminated during the analysis.

The error in titration of 100 cm 3 samples is 0.05 mol/m 3 .

Add 100 cm3 of filtered test water or a smaller volume diluted to 100 cm3 with distilled water into a conical flask. In this case, the total amount of the substance of the equivalent of calcium and magnesium ions in the taken volume should not exceed 0.5 mol. Then add 5 cm 3 of buffer solution, 5-7 drops of indicator or approximately 0.1 g of a dry mixture of black chromogen indicator with dry sodium and immediately titrate with strong shaking 0.05 N. Trilon B solution until the color changes at the equivalent point (the color should be blue with a greenish tinge).

If more than 10 cm 3 was used for titration, 0.05 n. Trilon B solution, this indicates that in a measured volume of water, the total amount of a substance equivalent to calcium and magnesium ions is more than 0.5 mol. In such cases, the determination should be repeated, taking a smaller volume of water and diluting it to 100 cm 3 with distilled water.

A fuzzy color change at the equivalent point indicates the presence of copper and zinc. To eliminate the influence of interfering substances, 1-2 cm 3 of sodium sulfide solution is added to the water sample measured for titration, after which the test is carried out as indicated above.

If, after adding a buffer solution and an indicator to a measured volume of water, the titrated solution gradually becomes discolored, acquiring a gray color, which indicates the presence of manganese, then in this case, five drops of a 1% solution should be added to the water sample taken for titration before adding reagents hydrochloric acid hydroxylamine and then determine the hardness as above.

If the titration becomes extremely protracted with an unstable and fuzzy color at the equivalent point, which is observed at high alkalinity of water, its effect is eliminated by adding water taken for titration to the sample before adding 0.1 N reagents. hydrochloric acid solution in the amount necessary to neutralize the alkalinity of water, followed by boiling or blowing the solution with air for 5 minutes. After that, a buffer solution is added, an indicator, and then the hardness is determined, as indicated above.

5. PROCESSING THE RESULTS

5.1. The total hardness of the water ( X), mol / m 3, calculated by the formula

where v- the amount of Trilon B solution used for titration, cm 3;

To- correction factor to the normality of the Trilon B solution;

V- the volume of water taken for determination, cm 3.

The discrepancy between repeated determinations should not exceed 2 rel. %.

(Revised edition, Rev. No. 1).

INFORMATION DATA

1. APPROVED AND PUT INTO EFFECT by the Decree of the State Committee of Standards of the Council of Ministers of the USSR dated 09.10.72 No. 1855

2. REPLACE GOST 4151-48

3. REFERENCE REGULATIONS AND TECHNICAL DOCUMENTS

4. The limitation of the validity period was removed by the Decree of the State Standard of the USSR of December 25, 1991 No. 2120

5. REPUBLICATION with Amendment No. 1 approved in June 1988 (IUS 11-88)