Water hardness is a set of chemical and physical properties of water associated with the content of dissolved salts of alkaline earth metals, mainly calcium and magnesium (the so-called “hardness salts”). Water is a complex natural substance that contains a whole range of microelements. In one form or another, water is found in all living organisms. What is meant by the concept of rigidity, and what determines this indicator?
Hardness is a property of water that determines its consumer qualities and is of great economic importance. During the boiling process, a hard liquid forms scale on the walls and internal parts of heating devices, which causes a deterioration in the thermal performance of household appliances. It is not particularly suitable for washing, since it helps to reduce the cleaning properties of detergents and increases their consumption.
Where does high rigidity come from? It is determined by the presence of magnesium and calcium salts - chemical components that act as active regulators of various chemical processes in the environment. Naturally, the liquid that is taken from different bodies of water may have one or another degree of hardness. At the same time, the river, lake and any other source are replenished from underground sources flowing in limestone layers. Passing through them, the water is enriched with hardness salts, which means it will be hard. For comparison, this indicator for surface waters is always noticeably lower than for groundwater. The hardness of water in natural sources is constantly changing. It reaches its maximum levels in winter, and minimum levels in spring, during the melting of snow.
Thus, hard water is the one that contains magnesium and calcium salts in large quantities. By the way, magnesium salts are less soluble than calcium salts, and liquids with a high content of them have a pronounced bitter taste.
The following types of rigidity are distinguished:
- Total - defined as the total concentration of magnesium and calcium ions.
- Carbonate - depends on the presence of carbonates, calcium and magnesium bicarbonates in the water. It is almost completely eliminated during boiling, so the second name for carbonate hardness is temporary. During the heating process, bicarbonates decompose - carbonic acid is formed, and calcium carbonates and magnesium hydroxides precipitate.
- Non-carbonate – due to the presence of magnesium and calcium acid salts. When boiled, it is not eliminated (that is, it is permanent).
Overall hardness is measured in GH. GH shows the total content of alkaline earth metals in the form of ions. For example, aquarium fish do not live in water with a GH value close to zero, and it is also not recommended to use it for food purposes.
In what units is hardness measured?
Different values are used around the world to measure hardness. In Russia, Gosstandart has established the following indicator - moles per cubic meter. The numerical value of hardness, which is expressed in moles per cubic meter, is equal to the numerical value of hardness in milligram equivalents per liter. In the West they use German (d°, dH), French (f°), American (ppm CaCO3) degrees.
How to increase and decrease water hardness in an aquarium. Determination of temporary or carbonate hardness
To create comfortable living conditions for aquarium fish, it is important to use water of optimal hardness, with a given acid-base balance. To increase water hardness, use limestone and marble. The softer the water, the faster it will increase hardness. Another method is chemical, using calcium chloride and magnesia. The maximum effect is achieved when using both drugs simultaneously.
To reduce hardness, water must be boiled. How long should this be done? Please note that to reduce the hardness by half, you need to boil the water for at least half an hour. Another method is freezing. Water is poured into a plastic container and placed in the freezer. Then the ice is melted, and the resulting water is used for food or any other purposes.
If the volumes of water are large, it will be easier to use special equipment. Reverse osmosis units have become widespread in everyday life in recent years. To calculate the required volume of tap water, use the formula - subtracting the volume of water obtained from the tap water from the volume with a given hardness that needs to be obtained.
Softening methods are often used in combination. For example, one part of the hardness salts is removed using a reagent method, and the other using cation exchange. Here are the formulas for the soda-lime softening method:
Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O
As a result, Mg(OH)2 coagulates and precipitates. Then, in order to eliminate non-carbonate hardness, Na2CO3 is introduced. Subsequent chemical reactions:
Na2CO3 + CaSO4 = CaCO3 + Na2SO4 and Na2CO3 + CaC12 = CaCO3 + 2NaCl.
As a result, calcium carbonate is formed, which then precipitates. Reagents are introduced into different zones:
- chlorine - into suction pipelines;
- coagulant - into the pipeline in front of the mixer or directly into the mixer;
- lime - together with a coagulant;
- activated carbon - in front of the filters;
- chlorine and ammonia - into filtered water.
Desalination, desalting, removal of dissolved gases, iron, stabilization are special cleaning methods. So, if cationization or ion exchange methods are used to reduce hardness, we are talking about desalting. The resulting water contains neither anions nor salt cations.
How to measure hardness
The following methods are used to assess water hardness:
- Complexometric titration with Trilon B. The method is complex and the most accurate.
- Purchased tests. Not 100% accurate, but simple and inexpensive.
- Electrical conductivity measurement. Use a conductivity meter.
- Using an ionometer and ion-selective electrodes.
- Using the method of titrating water samples with hydrochloric acid. A complex and not very accurate method. The same can be said about tests using laundry soap.
Titration means adding a reagent of the required concentration to water. The concentration of hardness salts is determined depending on the reaction of the reagent with water. Preparing the reagent is simple - just mix the acid with distilled water in the given proportions. The prepared solution is not dangerous.
The easiest way is to use ready-made texts. To do this, 5 ml of water is poured into a glass, then the contents of the dough are added dropwise to the liquid, after each drop the water is mixed. You need to do this until the color turns green instead of pink.
The influence of water hardness, regulatory requirements and recommendations
What kind of water can be used for cooking and drinking? Liquid hardness requirements depend on local conditions. Please note that too hard water has a bitter taste and negatively affects the functioning of the digestive system. WHO does not give specific figures, although studies on the connection between water quality and diseases of the heart, blood vessels and other organs of the body have been carried out repeatedly. Too soft water is also bad, since it disrupts the water-salt balance. A liquid with a hardness of 4 mg-equiv/ is fraught - the main cause of scale formation on the internal parts of heating systems. It is also harmful to skin and hair.
Instead of a conclusion
Hardness is an important parameter of water, which depends on the amount and type of minerals dissolved in it. Mitigation should be done only after preliminary analysis. Why? Because not all softening honeys reduce the content of minerals - they can simply convert hardness salts into salts that do not affect the indicator in any way.
Calcium and magnesium (Ca(HCO 3) 2; Mg(HCO 3) 2), and permanent (non-carbonate) hardness caused by the presence of other salts that are not released when water boils: mainly, sulfates And chlorides Ca and Mg (CaSO 4, CaCl 2, MgSO 4, MgCl 2).
When washing, hard water dries out the skin and makes it difficult to lather when using soap. The use of hard water causes the appearance of sediment (scale) on the walls of boilers, in pipes, etc. At the same time, the use of too soft water can lead to corrosion of pipes, since in this case there is no acid-base buffering, which is provided by hydrocarbonate water. (temporary) rigidity. Consumption of hard or soft water is usually not harmful to health; there is evidence that high hardness promotes the formation of urinary stones, and low hardness slightly increases the risk of cardiovascular disease. The taste of natural drinking water, for example, spring water, is due precisely to the presence of hardness salts.
The hardness of natural waters can vary over a fairly wide range and is not constant throughout the year. Hardness increases due to water evaporation and decreases during the rainy season, as well as during the melting of snow and ice.
Units
To numerically express the hardness of water, indicate the concentration of calcium and magnesium cations in it. The recommended SI unit for measuring concentration is mole per cubic meter (mol/m³), however, in practice degrees of hardness and milligram equivalent per liter (mg-equiv/L) are used to measure hardness.
On January 1, 2005, a new National Standard of the Russian Federation GOST R 52029-2003 “Water. Unit of rigidity". According to the new GOST, hardness is expressed in degrees of hardness (°Zh). 1 °F corresponds to a concentration of an alkaline earth element numerically equal to 1/2 of its mole per liter (1 °F = 1 mEq/l).
Sometimes the concentration is given per unit mass rather than volume, especially if the temperature of the water may vary or if the water may contain steam, which leads to significant changes in density.
Different countries used (sometimes still use) different non-systemic units - degrees of rigidity.
Water is classified according to its total hardness soft(up to 2 °F), medium hard(2-10 °F) and tough(more than 10 °F).
The hardness of water from surface sources fluctuates significantly throughout the year; it is maximum at the end of winter, minimum during the flood period (for example, the hardness of Volga water in March is 4.3 °F, in May - 0.5 °F). In groundwater, hardness is usually higher (up to 80-100 °F) and changes less throughout the year.
Elimination methods
Thermal softening. It is based on boiling water, as a result of which thermally unstable calcium and magnesium bicarbonates decompose with the formation of scale:
Ca(HCO 3) 2 → CaCO 3 ↓ + CO 2 + H 2 O.
Boiling removes only temporary (carbonate) hardness. Finds application in everyday life.
Reagent softening. The method is based on adding soda ash Na 2 CO 3 or slaked lime Ca (OH) 2 to water. In this case, calcium and magnesium salts turn into insoluble compounds and, as a result, precipitate. For example, adding slaked lime leads to the conversion of calcium salts into insoluble carbonate:
Ca(HCO 3) 2 + Ca(OH) 2 → 2CaCO 3 ↓ + 2H 2 O
The best reagent for eliminating general water hardness is sodium orthophosphate Na 3 PO 4, which is part of most preparations for household and industrial use:
3Ca(HCO 3) 2 + 2Na 3 PO 4 → Ca 3 (PO 4) 2 ↓ + 6NaHCO 3 3MgSO 4 + 2Na 3 PO 4 → Mg 3 (PO 4) 2 ↓ + 3Na 2 SO 4
Calcium and magnesium orthophosphates are very poorly soluble in water, so they are easily separated by mechanical filtration. This method is justified for relatively large water flows, since it is associated with solving a number of specific problems: sediment filtration, accurate dosage of the reagent.
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See what “Water hardness” is in other dictionaries: The set of properties of water due to the presence in it mainly of calcium and magnesium salts. The use of hard water leads to the deposition of solid sediment (scale) on the walls of steam boilers and heat exchangers, making it difficult to cook food... ...
encyclopedic Dictionary hardness of water - vandens kietumas statusas T sritis ekologija ir aplinkotyra apibrėžtis Vandens savybė, kurią lemia kalcio Ca²⁺ ir magnio Mg²⁺ jonų kiekis jame. Pagal kietumą vanduo skirstomas į: minkštą (kietumas4 mmol/l), vidutinio kietumo (4–8 mmol/l),… …
Ekologijos terminų aiškinamasis žodynas hardness of water)
encyclopedic Dictionary- - Topics oil and gas industry EN hardness ... - The amount of calcium and magnesium ions present in water and expressed in mg eq/l can be expressed in degrees of various systems. [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics: energy in general EN hardness of water ...
Technical Translator's Guide A set of properties determined by the content of Ca2+ and Mg2+ ions in water. The total concentration of Ca2+ ions (calcium fluid) and Mg2+ (magnesium fluid) is called total fluid. There are Zh. v. carbonate and non-carbonate. Carbonate liquid..... ...
Great Soviet Encyclopedia One of the indicators of water quality, conditioned. the content of dissolved calcium and magnesium salts in it, causing the deposition of solid sediment (scale) on the walls of heat exchangers (steam boilers, water heaters, etc.). Unit J.v. milligram... ...
Big Encyclopedic Polytechnic Dictionary The set of properties of water due to the presence of predominant elements in it. calcium and magnesium salts. Using hard water leads to sedimentation. sediment (scale) on the walls of steam boilers and heat exchangers makes it difficult to cook food. groceries, laundry...
Natural science. encyclopedic Dictionary The indicator of water mineralization, expressed by the total content of calcium and magnesium ions in it (in mg eq/l); used in assessing the quality of drinking water...
The property of water due to the content of calcium or magnesium salts in it, causing the formation of solid sediment (Bulgarian language; Български) hardness in water (Czech language; Čeština) tvrdost vody (German language; Deutsch) Wasserhärte (Hungarian... ... Construction dictionary
temporary hardness (water)- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics: energy in general EN temporary hardness... - The amount of calcium and magnesium ions present in water and expressed in mg eq/l can be expressed in degrees of various systems. [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics: energy in general EN hardness of water ...
This is water in which dissolved salts and alkaline earth metals are found in large quantities. Water hardness is mainly affected by calcium and magnesium, the compounds of which are the main hardness salts.
Rigidity determines not only the possibility, but also its use in domestic or industrial needs.
Taste Hard water is very easy to distinguish - it is extremely bitter. Sometimes the bitter taste of spring water is due to the presence of hardness salts.
By appearance can be found out after boiling. In this case, the salts precipitate, which is easily visible at the bottom of any vessel.
Classification of water by hardness
In Russia, water hardness is measured in degrees of hardness, but it can also be expressed in volume fraction or mass number.
An officially accepted unit of measurement that is used in the SI system ( international system of units) – moles per cubic meter. But in practice, the listed units of measurement are not used, preferring milliequivalent per liter (mg-equivalent/l).
Based on the level of hardness, water is divided into four types:
- Soft water (less than 2 milliequivalents per liter);
- Normal water (from 2 to 4 milliequivalents per liter);
- Hard water (4 to 6 milliequivalents per liter);
- Very hard water (6 or more milliequivalents per liter).
This classification is called American and is most often used when assessing water hardness.
There is a similar classification in degrees of hardness, but it represents only 3 types of water:
- Soft water (less than 2 degrees hardness);
- Water of medium hardness (from 2 to 10 degrees hardness);
- Extremely hard water (10 degrees hardness or more).
Water hardness standards
Water hardness standards in Russia and the world differ greatly from each other. In Russia, water is allowed whose hardness does not exceed a threshold of 7 milliequivalents per liter, that is, It is not prohibited to supply the population with very hard water.
The same figures in Europe cannot be higher 1,2 milliequivalents per liter. This means that Europeans drink soft water, the hardness of which is almost six times less than that established in Russia.
Types of water hardness based on susceptibility to heat treatment.
First type - temporary hardness, when in addition to calcium and magnesium, they are found in water hydrocarbonate anions. It is also called carbonate. It is easily removed by boiling water and does not affect the human body in any way.
Second type - constant hardness, also called non-carbonate rigidity. It is caused by the presence of calcium and magnesium compounds formed as a result of interaction with strong acids, for example, sulfuric or nitric. Such hardness is not removed by boiling water, because salts of this type do not disintegrate under the influence of temperature.
Overall hardness water is calculated by summing the indicators of carbonate and non-carbonate hardness.
The highest hardness values due to the abundance of dissolved salts are determined in sea and ocean water. The hardness of surface water is usually several times less than groundwater and moisture from underground sources.
Damage caused by hard water
Let's consider the negative impact of excessively hard water on the human body, household appliances and communications. The higher the hardness parameter, the stronger the value of each type of harmful effect.
Harm to human health and pets
- High rigidity promotes growth of urinary stones and the development of urolithiasis. This is due to the accumulation of salts that simply do not have time to be eliminated from the body.
- Hard water when washing dries out the skin. This is due to the appearance of “soap slag” formed from soap, which is not capable of lathering and dissolving in hard water. These soap slags clog the pores, preventing them from breathing freely, as a result of which skin inflammations can develop, and itching and burning of the skin can not rest.
- The formation of a thin crust on the hair destroys the natural fat film. This happens in the same way as on the skin of the hands - "soap slag" are not washed out and gradually accumulate. This may cause itchy scalp, dandruff and even hair loss.
- The effect of very hard water on animal health is no different from the effect on the human body. There is a high risk of developing urolithiasis. For pets eating dry food, this risk increases several times. Problems with hair and skin may occur in both dogs and cats when they are bathed regularly.
- Cooking process slows down, due to the numerous salts, the meat is poorly cooked. This leads to poor protein absorption and can cause gastrointestinal diseases.
Damage caused by hard water to equipment and household items
- Due to the presence of large amounts of salts in water, soap products are extremely foams poorly and removes dirt. Therefore, the amount of powders, detergents intended for washing dishes and other household chemicals will have to be increased sharply.
- In addition to poor foaming of soap products, due to contact of hard water with them streaks and hard deposits form on plumbing fixtures and the surface of dishes, as salt deposits form. Such deposits are difficult to wash off dishes and also negatively affect plumbing fixtures, gradually destroying their surfaces.
- In the process of heating water in electrical appliances, salts do not simply precipitate, but crystallize and fall out in the form of scale. It is scale that is the main reason for the rapid breakdown of water heating devices.
- Hard water leaves stains, stains and dirty deposits on freshly washed items, the color fades, prints and designs become gray. It is very difficult to get rid of them and this, again, requires increased consumption of detergents. Fabric washed in hard water becomes rough and inelastic because the salts clog up all the free space in it. The strength of clothing and linen decreases.
Harmful effects of water with increased hardness on communications
- Hardness salts, just like on household appliances, precipitate or crystallize, forming on the surface of communication paths and large devices and installations scale. Scale thins the walls of communications, subsequently completely destroying them.
- The abundance of hardness salts precipitated or scaled leads to frequent failure large water heating installations, such as boilers.
- In circulating water supply systems, scale deposits, water stones and salt sludge are formed reduce cross-country ability pipes, and heat transfer decreases. Water pressure drops, the amount of water in radiators decreases, water inlets and outlets from houses become clogged, which can lead to complete blockage of communication networks. All this increases energy costs.
At home, the most rational way to reduce water hardness is to purify water for drinking and cooking from excess salts. Ideally, water for any use in the home should be filtered.
But at the same time, we must not forget that the stiffness indicator must be equal to a certain average value. Water that is too soft is also of no benefit. It increases the risk of developing cardiovascular diseases in humans, flushes salts from the body, causing the rapid development of rickets and thinning of bones. In communication systems, soft water causes corrosion of metal pipes.
1. Using a Mohr pipette or cylinder, measure 50 ml of the test water and transfer it to a 250 ml conical titration flask.
2. Pour into the flask with a dispenser 2 ml solutionNaOH2 n.(to create an alkaline environment - pH 12-13) and add a dry indicator spatula to the tip fluorexone.
3. The sample is titrated to 0.02 N. Trilon B solution. Titration must be very careful; after adding a few drops of Trilon B, the contents of the flask are thoroughly mixed.
Color transition from greenish-pink fluorescent to pink testifies about the end of titration.
With further addition of Trilon B, the color of the water sample and its intensity do not change.
4. The amount of Trilon B used for titration is recorded in a notebook to calculate the content of calcium ions in the water being tested.
C =n * N* 1000 /V, Where
n- amount of Trilon B solution used for sample titration, ml
N- normality of Trilon B (see “Rigidity”);
V- sample volume taken for titration, ml
Recording and calculation of results.
Ca mg-eq/l= 4.9 * 0.0192 *1000 / 50 = 1.88 mEq/l
Ca mg/l =1.88 * 20.04 =37.7 mg/l
Reagents:
Trilon B solution (see the “Hardness” determination method)
2 n. sodium hydroxide solution (NaOH) 80 g, reagent grade. NaOH is dissolved in 1000 ml of distilled water (dissolution occurs with the release of heat).
ZnCl 2 solution (see "Hardness")
Mixed indicator - fluorexone (calcium disodium salt). Prepare as follows: 0.5 g of dry fluorexone is ground in small portions in a mortar with 100 g of sodium chloride. The prepared reagent should be stored in a dark glass bottle.
Magnesium.
Sources. The main source of magnesium ions in surface waters is the processes of chemical weathering and dissolution of dolomites, marls and other minerals. A significant amount of magnesium ions can enter reservoirs with wastewater from metallurgical, silicate, textile and other industries.
Properties and purposes of observation. Magnesium gives water a bitter taste, so its concentration in drinking water is limited.
In the test water sample, the total hardness (mg-eq/l) and the content of calcium ions are determined. The content of magnesium ions is determined arithmetically, calculating the value of calcium ions (mg-eq/l) from the total hardness value. The resulting value is the content of magnesium ions ( Mg 2+), mEq/l.
To convert mEq/L to mg/L, the resulting value in mEq/L is required. multiply by 12.16
Mg 2+ mg-eq/l + = 2.84 -1.88= 0.96 Mg 2+ mg/l= 0.96 * 12.16=11.7
One of the most frequently asked questions by Moscow residents is the question of the hardness of drinking water. This is due to the widespread use of dishwashers and washing machines in everyday life, for which the detergent load is calculated based on the actual hardness of the water used.
You can find out the water hardness value at your address using our electronic service
In Russia, hardness is measured in “degrees of hardness,” while global manufacturers use units of measurement accepted in their countries. Therefore, for the convenience of residents, a “Hardness Calculator” has been created, with which you can convert hardness values from one measurement system to another in order to correctly configure your household appliances.
| Hardness index | Current unit of measurement | Required unit of measurement | The result of the indicator calculation | |
|---|---|---|---|---|
| = |
Hardness is a set of properties of water associated with the content of dissolved salts in it, mainly calcium and magnesium ("hardness salts"). The total stiffness consists of temporary and permanent. Temporary hardness can be eliminated by boiling water, which is due to the property of some salts to precipitate, forming so-called scale.
The main factor influencing the value of hardness is the dissolution of rocks containing calcium and magnesium (limestones, dolomites) when natural water passes through them. Surface waters are generally softer than groundwater. The hardness of surface waters is subject to noticeable seasonal fluctuations, reaching a maximum in winter. Minimum values of hardness are typical for periods of high water or flood, when there is an intensive influx of soft melt or rainwater into water supply sources.
Hardness units
In Russia, hardness is measured in “degrees of hardness” (1°F = 1 mEq/l = 1/2 mol/m3). Other units of measurement of water hardness are accepted abroad.
Hardness units
1°F = 20.04 mg Ca 2 + or 12.15 Mg 2 + in 1 dm 3 of water;
1°DH = 10 mg CaO in 1 dm 3 water;
1°Clark = 10 mg CaCO 3 in 0.7 dm 3 water;
1°F = 10 mg CaCO 3 in 1 dm 3 water;
1 ppm = 1 mg CaCO 3 in 1 dm 3 water.
Water hardness in some cities around the world
World Health Organization (WHO) recommendations for drinking water:
calcium – 20-80 mg/l; magnesium – 10-30 mg/l. There is no recommended value for stiffness. According to these indicators, Moscow drinking water complies with WHO recommendations.
Russian regulatory documents (SanPiN 2.1.4.1074-01 and GN 2.1.5.1315-03) for drinking water regulate:
calcium – the standard has not been established; magnesium – no more than 50 mg/l; hardness - no more than 7°F.