Determination of water hardness. Determination of water hardness: GOST, instruments, methods Equipment, materials and reagents

Determining water hardness in the modern world is a prerequisite for ensuring the performance of all equipment working with it. However, it cannot be said that such a liquid is truly harmful to humans. Everything should be in moderation, because excessively soft water causes no less damage to health than hard water.

Concept of water hardness

You should always start from the very basics so that you have a complete understanding of the problem. In our case, before we begin to determine the hardness of water, we first need to understand what it is. According to the results of an examination carried out in 2011 at the Department of Chemistry and Ecology of Novgorod University. Yaroslav the Wise, for natural natural water, hardness is an absolutely normal phenomenon. Until the advent of modern technology, few people were interested in this issue; for thousands of years people calmly used it in the form in which it is. Magnesium and calcium salts dissolved in it give water hardness. The very concept of hardness arose as a result of people’s sensations, since when water saturated with these salts and other elements interacts with soap, virtually no foam is formed, making washing or washing difficult.

Types of hardness

Before you understand what kind of water to drink, you should take into account the fact that hardness is not a uniform value. There are at least two:

• Temporary.
• Constant.

These types depend on the type of dissolved salts, which are always present together in any hard water, making up the total hardness. Nevertheless, 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 decomposition, water itself, carbon dioxide and calcium carbonate, which is practically insoluble, are obtained directly. It turns out that you can get rid of temporary hardness without any problems by simply raising the water temperature to +100 degrees. Any teapot can be used as an example. After prolonged use, you can find sediment inside, which is the result of the decomposition process described above. However, everything that does not decompose in this way belongs to permanent hardness, which is almost impossible to get rid of without special treatment.

Why do you need to know water hardness?

This is necessary in order to understand what kind of water you can drink without danger, and also to ensure that any equipment that interacts with water does not break down. Excessively hard water is harmful to humans. But even if this parameter is at a level acceptable for our body, the equipment will still not be satisfied with it. Aquariums, coffee machines, washing machines, dishwashers, kettles, multicookers and many other types of equipment require water of a strictly defined hardness. Usually filters like “Geyser-3” help cope with this, but often such a measure may even be considered unnecessary. Before spending money on them, it is recommended to first test for water hardness, because it is quite possible that this indicator is already at a normal level.

Harm from hard and soft water

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

Effects of hard water:

• Poor dissolution of food products (associated with Ca 2 + and Mg 2 + cations).
• Coffee, tea and any other similar drinks brew very poorly.
• Long-term use may cause stomach relaxation.
• Hard water can cause kidney stones.
• Saturates the body with the elements it requires.
• Improves the condition of teeth and reduces the likelihood of caries.
• Hard water is the cause of failure of most types of equipment.

Effects of soft water:

• It removes toxins, but at the same time washes out useful elements (potassium, magnesium and calcium). As a result, bones become more fragile. It also does not have the best effect on the cardiovascular system.
• Negatively affects the pituitary-adrenal system.
• Has a bad effect on the water-salt balance of the body.

Thus, determining the hardness of water should not be done with the goal of getting rid of it, but in order to reduce the negative impact to a minimum and bring the consumption of such 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, using 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). Any container can be used as a container in which storage will be carried out, as long as it is made of glass or polymer 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 options, this option is deservedly considered the most reliable and comprehensive. It is based on the process of formation of trilon compounds together with alkaline earth element ions. The minimum stiffness indicator 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 hardness is to immediately visit the appropriate laboratory, since no home methods can provide accurate data. But more about them below.

There is no point in fully describing the entire process, since it is impossible to reproduce it yourself, without the necessary skills and chemical elements and equipment. Nevertheless, several basic principles of reaction can be identified that remain the same 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 rigidity.
• The analysis is carried out very quickly.
• The requirement that the process be stoichiometric must be met. Simply put, this means that no by-products should be formed during the reaction.
• Once a reaction begins, it cannot be reversed or stopped.

Test strips

To determine water hardness at home, you can use special devices, which are not difficult to buy (they are not prohibited and are publicly available). They look like standard test strips. To use, simply immerse one of them in water that requires testing for the period of time specified in the instructions. As a result, the product will change its color. When using such strips to determine water hardness, the main problem is determining exactly what the hardness value is. To do this, you need to compare the color on the strip and the examples with the description on the packaging. Unfortunately, it is not 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 your water is.

Home analysis

You can also check tap water for hardness using available means. True, this is more of an entertaining option than a real option for testing fluid readings.

You need to take:

• 1 liter jar (or any other similar container).
• A glass in the shape of a cylinder.
• Any scales (it is most convenient to use electronic ones).
• 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 this, distilled water should be heated, but not brought to a boil. It should be poured into the glass that already contains soap. As a result, it must dissolve in water. The next step is to add even more water. After this, you should pour regular tap water into the jar and slowly pour the soapy liquid from the glass and mix (slowly). If foam forms, then this is an indicator of hardness. 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 designed to determine what is affected both directly by salts (creating hardness) and by many other elements, which does not provide the required level of accuracy. Moreover, an ordinary person who does not know how to read them will not understand the readings of the device and will most likely get confused. Let's try to simplify the problem. The vast majority of such devices use some kind of ppm as units of measurement. We 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 mEq/l. These numbers are worth focusing on. If the device is domestic, everything becomes much easier. The worst thing is when such a device is made somewhere in China or another similar country that uses its own units of measurement. Then you will have to independently look for their equivalent and translate it into the readings we are familiar with.

AKMS-1

Among other devices capable of determining water hardness, the unique AKMS-1 device should be especially noted. This is a fairly large stationary unit, similar in size to the Geyser-3 filters. It is simply not possible to check the liquid at home using 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 react in a timely manner. Using this device, you can either release water 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 you save on equipment repairs, which will cost much more.

Results

Taking into account all of the above and the requirements of GOST, drinking water should be regularly checked for its hardness level. Nevertheless, it is not worth taking radical measures to soften it, since both conditions are harmful - too hard and too soft. Only in a situation where the indicators are really higher or lower is it worth taking some action. By the way, if you regularly struggle with hardness, then you almost never hear about too soft water, but you also need to pay no less attention to this.

STATE STANDARD OF THE USSR UNION

Date of introduction 01.01.74

This standard applies to drinking water and establishes a complexometric method for determining 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

Rectified ethyl alcohol according to GOST 5962.

Metal granulated zinc.

Magnesium sulfate - fixanal.

Chromogen black special ET-00 (indicator).

Chrome dark blue acidic (indicator).

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

3. PREPARATION FOR ANALYSIS

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

3.2. Preparation 0.05 n. Trilon B solution

9.31 g of Trilon B are dissolved in distilled water and adjusted to 1 dm3. If the solution is cloudy, then it is filtered. The solution is stable for several months.

3.3. Preparation of buffer solution

10 g of ammonium chloride (NH4Cl) is dissolved in distilled water, 50 cm3 of a 25% ammonia solution is added and adjusted to 500 cm3 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 indicator is dissolved in 20 cm3 of buffer solution and adjusted to 100 cm3 with ethyl alcohol. The dark blue chromium indicator solution can be stored for a long time without changing. 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 Na2S×9H2O or 3.7 g of Na2S×5H2O are dissolved in 100 cm3 of distilled water. The solution is stored in a bottle with a rubber stopper.

3.6. Preparation of hydroxylamine hydrochloride solution

1 g of hydroxylamine hydrochloride NH2OH×HCl is dissolved in distilled water and brought to 100 cm3.

3.7. Preparation 0.1 n. zinc chloride solution

An exact weighed portion of granulated zinc, 3.269 g, is dissolved in 30 cm3 of hydrochloric acid, diluted 1:1. Then adjust the volume in the volumetric flask to 1 dm3 with distilled water. Get exact 0.1 N. solution. By diluting this solution by half, 0.05 N is obtained. solution. If the sample is inaccurate (more or less than 3.269), then calculate the number of cubic centimeters of the original zinc solution to prepare an accurate 0.05 N. solution, which should contain 1.6345 g of zinc per 1 dm3.

3.8. Preparation 0.05 n. magnesium sulfate solution

The solution is prepared from the fixanal supplied with the set of reagents for determining water hardness and designed to prepare 1 dm3 of 0.01 N solution. To receive 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 cm3.

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

Add 10 cm3 of 0.05 N to a conical flask. zinc chloride solution or 10 cm3 0.05 N. solution of magnesium sulfate and diluted with distilled water to 100 cm3. Add 5 cm3 of buffer solution, 5-7 drops of indicator and titrate with strong shaking with Trilon B solution until the color changes at the equivalent point. The color should be blue with a violet tint when adding a dark blue chromium indicator and blue with a greenish tint when adding a black chromogen indicator.

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

The correction factor (K) to the normality of the Trilon B solution is calculated using the formula

where v is the amount of Trilon B solution consumed for titration, cm3.

4. ANALYSIS

4.1. The following factors interfere with the determination of total water hardness: copper, zinc, manganese and a high content of carbon dioxide and bicarbonate salts. The influence of interfering substances is eliminated during the analysis.

The error when titrating 100 cm3 of sample is 0.05 mol/m3.

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 substance equivalent to calcium and magnesium ions in the taken volume should not exceed 0.5 mol. Then add 5 cm3 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 with 0.05 N. Trilon B solution until the color changes at the equivalent point (the color should be blue with a greenish tint).

If more than 10 cm3 of 0.05 N was spent on titration. solution of Trilon B, this indicates that in the measured volume of water the total amount of 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 cm3 with distilled water.

A vague color change at the equivalent point indicates the presence of copper and zinc. To eliminate the influence of interfering substances, 1-2 cm3 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, indicating 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 the reagents hydroxylamine hydrochloride and then determine the hardness as indicated above.

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

(Changed edition, Amendment No. 1).

5. PROCESSING RESULTS

5.1. The total hardness of water (X), mol/m3, is calculated using the formula

,

where v is the amount of Trilon B solution consumed for titration, cm3;

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

V is the volume of water taken for determination, cm3.

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Preface

The goals and principles of standardization in the Russian Federation are established by Federal Law No. 184-FZ of December 27, 2002 “On Technical Regulation”, and the rules for applying national standards of the Russian Federation are GOST R 1.0-2004 “Standardization in the Russian Federation. Basic provisions"

Standard information

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

2 APPROVED AND ENTERED INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated December 20, 2005 No. 317-st

3 This standard takes into account the main normative provisions of the following ISO international 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 is published in the monthly published information index “National Standards”. In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the monthly published information index “National Standards”. Relevant information, notices and texts are also posted in the public information system - 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°F can cause the formation of sludge 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 its suitability for human consumption in terms of its taste properties.

In the complexometric (titrimetric) determination of hardness, ions of aluminum, cadmium, lead, iron, cobalt, copper, manganese, tin and zinc 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 determination. If the interfering influence cannot be eliminated, it is recommended to determine 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 (unit of hardness) in accordance with GOST R 52029.

Date of introduction - 2007-01-01

1 area of ​​use

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

Complexometric method (method A);

Atomic spectrometry methods (methods B and C).

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

Method B according to 5.2 is arbitrary in relation to other methods for determining rigidity.

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), 5 to 7 drops of an indicator solution (see) or from 0.05 to 0.1 g of a dry indicator mixture (see) and immediately titrate 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 used indicator eriochrome black T, and when using the indicator chrome dark blue acidic to blue (blue-violet).

The Trilon B solution is added quite quickly at the beginning of the titration 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 adding drops of Trilon B solution.

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 arithmetic mean of the results of at least two determinations is taken as the result.

Correction factor TO to the concentration of Trilon B solution is calculated using the formula

,(1)

Where V- volume of Trilon B solution consumed for titration, cm 3;

10 - volume of solution of magnesium ions (cm), 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°F.

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

|AND L 1 - AND L 2 | ≤ Rµ (5)

Where AND L 1, AND L 2 - measurement results obtained in two laboratories, °W;

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

µ - actual (reference) value of stiffness in the comparison sample, °Zh.

Note - If the hardness in the GSO used is expressed in mmol/dm 3 (mol/m 3), then it is necessary to convert it 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 °W.

In accordance with the manual (instructions) for operating 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 solution of hydrochloric acid. Calibration dependences of the absorption of calcium and magnesium on their content in calibration solutions are established using the arithmetic mean values ​​of the results of three measurements for each calibration solution minus the arithmetic mean value of the results of three measurements of the blank solution.

5.1.4.3 The stability of calibration dependencies is monitored 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.

5.1.5 Preparation of samples for analysis

In volumetric flasks with a capacity of 100 cm 3 add 10 cm 3 of lanthanum chloride solution if using an air-acetylene flame, or 10 cm 3 of cesium chloride solution if using a nitrous oxide-acetylene flame, then add an aliquot of a water sample (usually no more than 10 cm 3) and bring to the mark with a solution of hydrochloric acid (see).

If the measured calcium or magnesium content in the test sample is higher than the maximum values ​​​​set during 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 (instructions) for operating the spectrometer, analyzed solutions prepared according to are introduced into it, and in the intervals between them - a solution of hydrochloric acid (see). The absorbance of each element at the analytical wavelength is determined.

5.1.6.2 At the same time, conduct a blank experiment using the same reagents and in the same quantities as when preparing samples according to 5.1.5, replacing the test volume of the analyzed sample with double-distilled water.

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

5.1.7 Processing determination results

Using the calibration dependence (see), including using the spectrometer software, determine the mass concentrations of calcium and magnesium in the solutions under study and in the blank solution and calculate the calcium and magnesium content 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 AND, °Zh, calculated by the formula

AND = ∑(WITH i/ WITH i e )· F· V To / V p ,(7)

Where WITH i , is the mass concentration of the element in the water sample, determined from 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 canning (usuallyF = 1);

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

V P - volume of water sample taken for analysis, cm3.

5.1.8 Metrological characteristics

The method provides measurement results for 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 determination results - according to. Instead of the GSO composition of water hardness, you can use the GSO composition of aqueous solutions of magnesium and calcium ions. The values ​​of repeatability and reproducibility limits are in accordance with Table 3.

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

,(8)

Where Δ e - boundaries of the interval in which the error in measuring an element in a water sample lies with a confidence probability R= 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 water hardness taking into account the content of other alkaline earth elements, the determination of strontium ions is carried out using 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 element ions by inductively coupled plasma atomic emission spectrometry (method B)

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

Hardness of water AND, °Zh, calculated by the formula

AND= ∑(C i /C 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 GSO composition of water hardness, you can use the GSO composition of aqueous solutions of magnesium, calcium, barium, strontium ions; values ​​of repeatability (convergence) and reproducibility limits - according to GOST R 51309 (Table 4).

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

,(10)

where δ is the boundaries of the interval in which the relative error in determining the element is found with confidence probability R= 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 ;

S 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% (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.

The essence of the method is the formation of a strong complex of the Trilon B compound with calcium and magnesium ions, accompanied by a change in the color of the corresponding indicator.

The determination is carried out by titrating the sample with a solution of Trilon B in the presence of the indicators eriochrome black T or chrome dark blue.

The sensitivity of the method is from 0.5 mEq./L.

The range of determined values ​​is from 0.5 to 20 mEq/l.

The kit allows you to determine water hardness in the presence of copper, manganese and zinc cations.

Necessary for analysis devices and materials:

Dishes:

Volumetric flasks 2-1000-2 according to GOST 1770.
Flasks Kn-250 THS according to GOST 25336E.
Burette 1-2-25-0.1 according to GOST 29251.
Measuring cylinders with a capacity of 100 cm 3 according to GOST 1770
Measuring pipettes graduated by 10 according to GOST 29227.

Reagents:

Distilled water according to GOST 6709 (desalted water, condensate).

Contents of the set.

Magnesium sulfate, standard titer for preparing a solution with a concentration of 0.01 g-eq/dm 3 - 1 pc.
Magnesium sulfate, standard titer for preparing a solution with a concentration of 0.1 g-equiv/dm 3 - 1 pc.
Trilon B, standard titer for preparing a solution with a concentration of 0.1 g-equiv/dm 3 - 1 pc.
Trilon B, standard titer for preparing a solution with a concentration of 0.05 g-eq/dm 3 - 7 pcs.
Trilon B, standard titer for preparing a solution with a concentration of 0.01 g-equiv/dm 3 - 1 pc.
Ammonium chloride, analytical grade. according to GOST 3773, 5 packs of 20 g.
Ammonia, aqueous, 25% solution, analytical grade. according to GOST 3760, total volume 500 ml
Eriochrome black T, dry mixture, weighed 50 g
Chrome dark blue, dry mix, weighed 50 g
Hydroxylamine hydrochloride, analytical grade. according to GOST 5456, weighed 1 g
Na-diethyldithiocarbamate, analytical grade, according to GOST 8864, weighed 3 g

Additional equipment: for determining hardness in the presence of copper and zinc ions - Na-diethyldithiocarbamate, analytical grade, according to GOST 8864, 7.5 g sample for preparing 250 cm 3 of working solution.

The reagents included in the kit are tested for compliance with the requirements of current standards and technical specifications.

Correction factors for the normality of standard solutions are within the range of 1±0.003.

Preparing for analysis.

For the preparation of Trilon B solutions it is necessary to quantitatively transfer the contents of the ampoule into a 1000 ml volumetric flask, dissolve in approximately 800-900 ml of distilled water (within 1.5-2 hours) and bring the volume of the solution to the mark with distilled water.

The time spent on the operation is about 2 hours.

The correction factor for solutions prepared from standard titres is equal to unity.

To prepare a buffer solution it is necessary to place the contents of one package of ammonium chloride in a 1000 ml volumetric flask, dissolve in approximately 300 ml of distilled water, add 100 ml of aqueous ammonia measured with a cylinder. Stir well until the ammonium chloride is completely dissolved (within 5-10 minutes) and bring the volume of the solution to the mark with distilled water.

The time spent on the operation is about 30 minutes.

The set is suitable for determining

Hardness of raw and clarified water in the absence of copper, zinc and manganese cations;
- water hardness in the presence of copper and zinc cations;
- water hardness in the presence of manganese cations;
- residual hardness after liming;
- hardness of water contaminated with oil products;
- very low hardness values ​​using the back titration method;
- hardness of condensate and softened water in the absence of copper, zinc and manganese cations.

Designation	GOST 4151-72
Title in Russian	Drinking water. Methods for determining total hardness
Title in English	Drinking water. Method for determination of total hardness
Effective date	01.01.1974
Date limit validity period	01.01.2007
OKS	13.060.20
OKP code	910000
KGS code	H09
OKSTU code	9109
Index of the GRNTI rubricator	610181
Abstract (scope of application)	This standard applies to drinking water and establishes a complexometric method for determining total hardness. The method is based on the formation of a strong complex compound of Trilon B with calcium and magnesium ions. Determination is carried out by titrating the sample with Trilon B at pH 10 in the presence of an indicator
Type of standard	Standards for control methods
Designation of the replacement(s)	GOST 4151-48
Normative references to: GOST	GOST 2874-54; GOST 4979-49; GOST 1770-64; GOST 10394-63; GOST 9876-61; GOST 10652-63; GOST 3773-60; GOST 3760-64; GOST 5456-65; GOST 3118-67; GOST 2053-66; GOST 4233-66; GOST 5962-67; GOST 989-62
Rostekhregulirovaniya Department	420 - Department of Standardization and Certification of Food, Light Industry and Agricultural Products
MND developer	Russian Federation
Last edition date	01.09.2002
Change number(s)	reissue with changes 1
Number of pages (original)	6
Status	Lost force in the Russian Federation
Use on the territory of the Russian Federation	GOST R 52407-2005

GOST 4151-72

STATE STANDARD OF THE USSR UNION

DRINKING WATER

Method for determining total hardness

Method for determination

of total hardness content

Date of introduction 01.01.74

This standard applies to drinking water and establishes a complexometric method for determining 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 a measured volume of water, diluted 1:1 with distilled water, can be left for determination until the next day.

Water samples intended to determine total hardness are not preserved.

2. EQUIPMENT, MATERIALS AND REAGENTS

Measuring laboratory glassware in accordance with GOST 1770 with a capacity: pipettes 10, 25, 50 and 100 cm 3 without divisions; burette 25 cm 3 .

Conical flasks 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.

Aqueous ammonia according to GOST 3760, 25% solution.

Hydroxylamine hydrochloric acid according to GOST 5456.

Citric acid according to GOST 3118.

Sodium sulphide (sodium sulfide) according to GOST 2053.

Sodium chloride according to GOST 4233.

Rectified ethyl alcohol according to GOST 5962.

Metal granulated zinc.

Magnesium sulfate - fixanal.

Chromogen black special ET-00 (indicator).

Chrome dark blue acidic (indicator).

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

3. PREPARATION FOR ANALYSIS

3.1. Distilled water, double distilled in a glass apparatus, is used to dilute 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. Preparation of buffer solution

10 g of ammonium chloride (NH 4 Cl) is dissolved in distilled water, 50 cm 3 of a 25% ammonia solution is added and adjusted 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 indicator is dissolved in 20 cm 3 of 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 changing. 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 sulphide Na 2 SCh9H 2 O or 3.7 g Na 2 SCh5H 2 O are dissolved in 100 cm 3 of distilled water. The solution is stored in a bottle with a rubber stopper.

3.6. Preparation of hydroxylamine hydrochloride solution

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

3.7. Preparation 0.1 n. zinc chloride solution

An exact weighed portion of granulated zinc, 3.269 g, is dissolved in 30 cm 3 of hydrochloric acid, diluted 1:1. Then the volume in the volumetric flask is adjusted to 1 dm 3 with distilled water. Get exact 0.1 N. solution. By diluting this solution by half, 0.05 N is obtained. solution. If the sample is inaccurate (more or less than 3.269), then calculate the number of cubic centimeters of the original zinc solution to prepare an accurate 0.05 N. solution, which should contain 1.6345 g of zinc per 1 dm 3.

3.8. Preparation 0.05 n. magnesium sulfate solution

The solution is prepared from the fixanal supplied with the set of reagents for determining water hardness and designed to prepare 1 dm 3 0.01 N solution. To receive 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 a correction factor for the normality of the Trilon B solution

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

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

Correction factor ( TO) to the normality of the Trilon B solution is calculated using the formula

Where v- the amount of Trilon B solution consumed for titration, cm 3.

4. ANALYSIS

4.1. The following factors interfere with the determination of total water hardness: copper, zinc, manganese and a high content of carbon dioxide and bicarbonate salts. The influence of interfering substances is eliminated during the analysis.

The error when titrating 100 cm3 of sample is 0.05 mol/m3.

Add 100 cm 3 of filtered test water or a smaller volume diluted to 100 cm 3 with distilled water into a conical flask. In this case, the total amount of substance equivalent to 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 with 0.05 N. Trilon B solution until the color changes at the equivalent point (the color should be blue with a greenish tint).

If more than 10 cm 3 0.05 N was spent on titration. solution of Trilon B, this indicates that in the measured volume of water the total amount of 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 vague 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, indicating 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 the reagents hydroxylamine hydrochloride and then determine the hardness as indicated above.

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

5. PROCESSING RESULTS

5.1. Total water hardness ( X), mol/m3, calculated using the formula

Where v- the amount of Trilon B solution consumed for titration, cm 3;

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

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

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

(Changed edition, Amendment No. 1).

INFORMATION DATA

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

2. INSTEAD GOST 4151-48

3. REFERENCE REGULATIVE AND TECHNICAL DOCUMENTS

	Item number
GOST 1770-74
GOST 2053-77
GOST 2874-82
GOST 3118-77
GOST 3760-79
GOST 3773-72
GOST 4233-77
GOST 4979-49
GOST 5456-79
GOST 5962-67
GOST 10652-73
GOST 25336-82

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

5. REISSUE with Change No. 1, approved in June 1988 (IUS 11-88)

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