What is an acidic environment pH? Acidity of the environment. The concept of solution pH. Effect of temperature on pH values

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  In pure water at 22 °C, the concentrations of hydrogen ions () and hydroxide ions () are the same and amount to 10 −7 mol/l, this directly follows from the definition of the ionic product of water, which is equal to · and amounts to 10 −14 mol²/l² (at 25 °C).

  When the concentrations of both types of ions in a solution are equal, the solution is said to have neutral reaction. When an acid is added to water, the concentration of hydrogen ions increases, and the concentration of hydroxide ions correspondingly decreases; when a base is added, on the contrary, the content of hydroxide ions increases, and the concentration of hydrogen ions decreases. When > they say that a solution is acidic, and when > - main.

  For convenience of presentation, in order to get rid of the negative exponent, instead of the concentrations of hydrogen ions, their decimal logarithm is used, taken with the opposite sign, which, in fact, is the hydrogen exponent - pH.

  pH = − log ⁡ [ H + ] (\displaystyle (\mbox(pH))=-\lg \left[(\mbox(H))^(+)\right])

  pOH

  The inverse pH value is somewhat less widespread - an indicator of the basicity of the solution, pOH, equal to the negative decimal logarithm of the concentration of OH ions in the solution:

  as in any aqueous solution at 25 °C [ H + ] [ OH − ] = 1 , 0 ⋅ 10 − 14 (\displaystyle [(\text(H))^(+)][(\text(OH))^(-)]=1(,) 0\cdot 10^(-14)), it is obvious that at this temperature:

  pOH = 14 − pH (\displaystyle (\text(pOH))=14-(\text(pH)))

  pH values ​​in solutions of varying acidity

  • Contrary to popular belief, pH can vary not only in the range from 0 to 14, but can also go beyond these limits. For example, at a hydrogen ion concentration = 10 −15 mol/l, pH = 15, at a hydroxide ion concentration of 10 mol/l pOH = −1.

  Some pH values ​​[ ] Substance pH Indicator color Electrolyte in lead batteries <1,0 Gastric juice 1,0–2,0 Lemon juice (5% citric acid solution) 2.0±0.3 Food vinegar 2,4 Apple juice 3,0 Coca Cola 3.0±0.3 Beer 4,5 Coffee 5,0 Shampoo 5,5 Tea 5,5 Healthy skin 5,5 Acid rain < 5,6 Drinking water 6,5–8,5 Milk 6,6–6,93 Saliva 6,8–7,4 Pure water at 25 °C 7,0 Blood 7,36–7,44 Sperm 7,2–8,0 Sea water 8,0 Soap (fat) for hands 9,0–10,0 Ammonia 11,5 Bleach (bleach) 12,5 Concentrated alkali solutions >13

  Since at 25 °C (standard conditions) = 10 −14, it is clear that at this temperature pH + pOH = 14.

  Since in acidic solutions > 10 −7, then the pH of acidic solutions< 7, аналогично, у основных растворов pH >7, the pH of neutral solutions is 7. At higher temperatures, the electrolytic dissociation constant of water increases, and the ionic product of water increases accordingly, so the pH turns out to be neutral< 7 (что соответствует одновременно возросшим концентрациям как H + , так и OH −); при понижении температуры, напротив, нейтральная pH возрастает.

  Methods for determining pH value

  Several methods are widely used to determine the pH value of solutions. The pH value can be approximately estimated using indicators, measured accurately with a pH meter, or determined analytically by performing acid-base titration.

  1. To roughly estimate the concentration of hydrogen ions, acid-base indicators are widely used - organic dye substances, the color of which depends on the pH of the environment. The most well-known indicators include litmus, phenolphthalein, methyl orange (methyl orange) and others. Indicators can exist in two differently colored forms - either acidic or basic. The color change of each indicator occurs in its own acidity range, usually 1–2 units.
  2. To expand the working range of pH measurements, a so-called universal indicator is used, which is a mixture of several indicators. The universal indicator sequentially changes color from red through yellow, green, blue to violet when moving from the acidic region to the basic one. Determining pH by the indicator method is difficult for cloudy or colored solutions.
  3. The use of a special device - a pH meter - allows you to measure pH in a wider range and more accurately (up to 0.01 pH units) than using indicators. The ionometric method for determining pH is based on measuring the EMF of a galvanic circuit with a millivoltmeter-ionometer, including a special glass electrode, the potential of which depends on the concentration of H + ions in the surrounding solution. The method is convenient and highly accurate, especially after calibrating the indicator electrode in a selected pH range; it allows you to measure the pH of opaque and colored solutions and is therefore widely used.
  4. The analytical volumetric method - acid-base titration - also provides accurate results for determining the acidity of solutions. A solution of known concentration (titrant) is added dropwise to the test solution. When they are mixed, a chemical reaction occurs. The equivalence point - the moment when there is exactly enough titrant to completely complete the reaction - is recorded using an indicator. Next, knowing the concentration and volume of the added titrant solution, the acidity of the solution is calculated.

  The role of pH in chemistry and biology

  The acidity of the environment is important for many chemical processes, and the possibility or outcome of a particular reaction often depends on the pH of the environment. To maintain a certain pH value in the reaction system during laboratory research or in production, buffer solutions are used, which allow maintaining an almost constant pH value when diluted or when small amounts of acid or alkali are added to the solution.

  The pH value is widely used to characterize the acid-base properties of various biological media.

  The acidity of the reaction medium is of particular importance for biochemical reactions occurring in living systems. The concentration of hydrogen ions in a solution often affects the physicochemical properties and biological activity of proteins and nucleic acids, therefore, for the normal functioning of the body, maintaining acid-base homeostasis is a task of exceptional importance. Dynamic maintenance of the optimal pH of biological fluids is achieved through the action of the body's buffer systems.

  In the human body, the pH value is different in different organs.

  Acidity(lat. aciditas) - characteristic of the activity of hydrogen ions in solutions and liquids.

  In medicine, the acidity of biological fluids (blood, urine, gastric juice and others) is a diagnostically important parameter of the patient’s health status. In gastroenterology, for the correct diagnosis of a number of diseases, for example, the esophagus and stomach, a one-time or even average acidity value is not significant. Most often, it is important to understand the dynamics of changes in acidity during the day (night acidity often differs from daytime) in several zones of the organ. Sometimes it is important to know the change in acidity as a reaction to certain irritants and stimulants.

  pH value

  In solutions, inorganic substances: salts, acids and alkalis are separated into their constituent ions. In this case, hydrogen ions H + are carriers of acidic properties, and OH − ions are carriers of alkaline properties. In highly dilute solutions, the acidic and alkaline properties depend on the concentrations of H + and OH − ions. In ordinary solutions, acidic and alkaline properties depend on the activities of the ions a H and a OH, that is, on the same concentrations, but adjusted for the activity coefficient γ, which is determined experimentally. For aqueous solutions, the equilibrium equation applies: a H × a OH = K w, where K w is a constant, the ionic product of water (K ​​w = 10 − 14 at a water temperature of 22 °C). From this equation it follows that the activity of hydrogen ions H + and the activity of OH − ions are interconnected. Danish biochemist S.P.L. Sørensen proposed a hydrogen show in 1909 pH, equal by definition to the decimal logarithm of the activity of hydrogen ions, taken with a minus (Rapoport S.I. et al.):
  

  
  pH = - log (a N).

  Based on the fact that in a neutral environment a H = a OH and from the equality for pure water at 22 °C: a H × a OH = K w = 10 − 14, we obtain that the acidity of pure water at 22 °C (then there is neutral acidity) = 7 units. pH.

  Solutions and liquids with respect to their acidity are considered:

  • neutral at pH = 7
  • acidic at pH< 7
  • alkaline at pH > 7

  Some misconceptions

  If one of the patients says that he has “zero acidity,” then this is nothing more than a turn of phrase, meaning, most likely, that he has a neutral acidity value (pH = 7). In the human body, the acidity value cannot be less than 0.86 pH. It is also a common misconception that acidity values ​​can only range from 0 to 14 pH. In technology, the acidity indicator can be negative or greater than 20.

  When talking about the acidity of an organ, it is important to understand that acidity can often differ significantly in different parts of the organ. The acidity of the contents in the lumen of the organ and the acidity on the surface of the mucous membrane of the organ are also often not the same. It is typical for the mucous membrane of the body of the stomach that the acidity on the surface of the mucus facing the lumen of the stomach is 1.2–1.5 pH, and on the side of the mucus facing the epithelium it is neutral (7.0 pH).

  pH value for some foods and water

  The table below shows the acidity values ​​of some common foods and pure water at different temperatures:

  Product	Acidity, units pH
  Lemon juice	2,1
  Wine	3,5
  Tomato juice	4,1
  Orange juice	4,2
  Black coffee	5,0
  Pure water at 100 °C	6,13
  Pure water at 50 °C	6,63
  Fresh milk	6,68
  Pure water at 22 °C	7,0
  Pure water at 0°C	7,48

  Acidity and Digestive Enzymes

  Many processes in the body are impossible without the participation of special proteins - enzymes, which catalyze chemical reactions in the body without undergoing chemical transformations. The digestive process is not possible without the participation of a variety of digestive enzymes, which break down various organic food molecules and act only in a narrow range of acidity (different for each enzyme). The most important proteolytic enzymes (break down food proteins) of gastric juice: pepsin, gastrixin and chymosin (rennin) are produced in an inactive form - in the form of proenzymes and are later activated by hydrochloric acid of gastric juice. Pepsin is most active in a strongly acidic environment, with a pH of 1 to 2, gastrixin has maximum activity at pH 3.0–3.5, chymosin, which breaks down milk proteins into insoluble casein protein, has maximum activity at pH 3.0–3.5 .

  Proteolytic enzymes secreted by the pancreas and “acting” in the duodenum: trypsin has an optimum action in a slightly alkaline environment, at pH 7.8–8.0; chymotrypsin, which is close to it in functionality, is most active in an environment with an acidity of up to 8.2. The maximum activity of carboxypeptidases A and B is 7.5 pH. Similar maximum values ​​are found for other enzymes that perform digestive functions in the slightly alkaline environment of the intestine.

  Reduced or increased acidity relative to the norm in the stomach or duodenum, thus, leads to a significant decrease in the activity of certain enzymes or even their exclusion from the digestive process, and, as a consequence, to digestive problems.

  Acidity of saliva and oral cavity

  The acidity of saliva depends on the rate of salivation. Typically, the acidity of mixed human saliva is 6.8–7.4 pH, but with high salivation rates it reaches 7.8 pH. The acidity of the saliva of the parotid glands is 5.81 pH, of the submandibular glands - 6.39 pH.

  In children, on average, the acidity of mixed saliva is 7.32 pH, in adults - 6.40 pH (Rimarchuk G.V. et al.).

  The acidity of dental plaque depends on the condition of the hard tissues of the teeth. Being neutral in healthy teeth, it shifts to the acidic side, depending on the degree of development of caries and the age of adolescents. In 12-year-old adolescents with the initial stage of caries (precaries), the acidity of dental plaque is 6.96 ± 0.1 pH, in 12–13-year-old adolescents with average caries, the acidity of dental plaque is from 6.63 to 6.74 pH, in 16 -year-old adolescents with superficial and medium caries, the acidity of dental plaque is, respectively, 6.43 ± 0.1 pH and 6.32 ± 0.1 pH (Krivonogova L.B.).

  Acidity of the secretion of the pharynx and larynx

  The acidity of the secretion of the pharynx and larynx in healthy people and patients with chronic laryngitis and pharyngolaryngeal reflux is different (A.V. Lunev):

  Groups of surveyed	pH measurement location
  	Pharynx, units pH	Larynx, units pH
  Healthy faces
  Patients with chronic laryngitis without GERD		The figure above shows a graph of acidity in the esophagus of a healthy person, obtained using intragastric pH-metry (Rapoport S.I.). The graph clearly shows gastroesophageal refluxes - sharp decreases in acidity to 2-3 pH, which in this case are physiological. Acidity in the stomach. Increased and decreased acidity The maximum observed acidity in the stomach is 0.86 pH, which corresponds to an acid production of 160 mmol/l. The minimum acidity in the stomach is 8.3 pH, which corresponds to the acidity of a saturated solution of HCO 3 - ions. Normal acidity in the lumen of the body of the stomach on an empty stomach is 1.5–2.0 pH. The acidity on the surface of the epithelial layer facing the lumen of the stomach is 1.5–2.0 pH. The acidity in the depths of the epithelial layer of the stomach is about 7.0 pH. Normal acidity in the antrum of the stomach is 1.3–7.4 pH. The cause of many diseases of the digestive tract is an imbalance in the processes of acid production and acid neutralization. Long-term hypersecretion of hydrochloric acid or lack of acid neutralization, and, as a consequence, increased acidity in the stomach and/or duodenum, causes so-called acid-dependent diseases. Currently, these include: peptic ulcer of the stomach and duodenum, gastroesophageal reflux disease (GERD), erosive and ulcerative lesions of the stomach and duodenum while taking aspirin or non-steroidal anti-inflammatory drugs (NSAIDs), Zollinger-Ellison syndrome, gastritis and gastroduodenitis with high acidity and others. Low acidity is observed with anacid or hypoacid gastritis or gastroduodenitis, as well as with stomach cancer. Gastritis (gastroduodenitis) is called anacid or gastritis (gastroduodenitis) with low acidity if the acidity in the body of the stomach is approximately 5 units or more. pH. The cause of low acidity is often atrophy of parietal cells in the mucous membrane or disturbances in their functions. Above is a graph of the acidity (daily pH gram) of the body of the stomach of a healthy person (dashed line) and a patient with a duodenal ulcer (solid line). Moments of eating are marked with arrows labeled “Food”. The graph shows the acid-neutralizing effect of food, as well as increased stomach acidity with duodenal ulcer (Yakovenko A.V.). Acidity in the intestines Normal acidity in the duodenal bulb is 5.6–7.9 pH. The acidity in the jejunum and ileum is neutral or slightly alkaline and ranges from 7 to 8 pH. The acidity of small intestine juice is 7.2–7.5 pH. With increased secretion it reaches 8.6 pH. The acidity of the secretion of the duodenal glands is from pH 7 to 8 pH. Measuring point Point number in the figure Acidity, units pH Proximal sigmoid colon 7 7.9±0.1 Middle sigmoid colon 6 7.9±0.1 Distal sigmoid colon 5 8.7±0.1 Supraampullary rectum 4 8.7±0.1 Upper ampullary rectum 3 8.5±0.1 Mid-ampullary rectum 2 7.7±0.1 Inferior ampullary rectum 1 7.3±0.1 Stool acidity The acidity of the feces of a healthy person eating a mixed diet is determined by the vital activity of the colon microflora and is equal to 6.8–7.6 pH. Stool acidity is considered normal in the range from 6.0 to 8.0 pH. The acidity of meconium (original feces of newborns) is about 6 pH. Deviations from the norm for stool acidity: sharply acidic (pH less than 5.5) occurs with fermentative dyspepsia acidic (pH from 5.5 to 6.7) may be due to impaired absorption of fatty acids in the small intestine alkaline (pH from 8.0 to 8.5) may be due to the rotting of food proteins not digested in the stomach and small intestine and inflammatory exudate as a result of activation of putrefactive microflora and the formation of ammonia and other alkaline components in the large intestine sharply alkaline (pH more than 8.5) occurs with putrefactive dyspepsia (colitis) Blood acidity The acidity of human arterial blood plasma ranges from 7.37 to 7.43 pH, averaging 7.4 pH. The acid-base balance in human blood is one of the most stable parameters, maintaining acidic and alkaline components in a certain balance within very narrow limits. Even a small shift from these limits can lead to severe pathology. When shifting to the acidic side, a condition called acidosis occurs, and to the alkaline side, alkolosis occurs. A change in blood acidity above 7.8 pH or below 6.8 pH is incompatible with life. The acidity of venous blood is 7.32–7.42 pH. The acidity of red blood cells is 7.28–7.29 pH. Acidity of urine In a healthy person with a normal drinking regime and a balanced diet, the acidity of urine is in the range from 5.0 to 6.0 pH, but can range from 4.5 to 8.0 pH. The acidity of the urine of a newborn under the age of one month is normal - from 5.0 to 7.0 pH. The acidity of urine increases if a person’s diet is dominated by meat foods rich in proteins. Heavy physical work increases the acidity of urine. A dairy-vegetable diet causes urine to become slightly alkaline. An increase in urine acidity is observed with increased stomach acidity. Reduced acidity of gastric juice does not affect the acidity of urine. A change in urine acidity most often corresponds to a change. The acidity of urine changes with many diseases or conditions of the body, so determining the acidity of urine is an important diagnostic factor. Vaginal acidity The normal acidity of a woman's vagina ranges from 3.8 to 4.4 pH and averages 4.0 to 4.2 pH. Vaginal acidity in various diseases: cytolytic vaginosis: acidity less than 4.0 pH normal microflora: acidity from 4.0 to 4.5 pH candidal vaginitis: acidity from 4.0 to 4.5 pH trichomonas colpitis: acidity from 5.0 to 6.0 pH bacterial vaginosis: acidity greater than 4.5 pH atrophic vaginitis: acidity greater than 6.0 pH aerobic vaginitis: acidity greater than 6.5 pH Lactobacilli (lactobacillus) and, to a lesser extent, other representatives of normal microflora are responsible for maintaining an acidic environment and suppressing the growth of opportunistic microorganisms in the vagina. In the treatment of many gynecological diseases, restoration of the lactobacilli population and normal acidity comes to the fore. Publications for healthcare professionals addressing the issue of acidity in the female genital organs Murtazina Z.A., Yashchuk G.A., Galimov R.R., Dautova L.A., Tsvetkova A.V. Office diagnostics of bacterial vaginosis using hardware topographic pH-metry. Russian Bulletin of Obstetrician-Gynecologist. 2017;17(4): 54-58. Gasanova M.K. Modern approaches to the diagnosis and treatment of serozometra in postmenopause. Abstract of dissertation. PhD, 14.00.01 - obstetrics and gynecology. RMAPO, Moscow, 2008. Sperm acidity The normal acidity level of sperm is between 7.2 and 8.0 pH. Deviations from these values ​​are not in themselves considered pathology. At the same time, in combination with other deviations, it may indicate the presence of a disease. An increase in the pH level of sperm occurs during an infectious process. A sharply alkaline reaction of sperm (acidity approximately 9.0–10.0 pH) indicates prostate pathology. When the excretory ducts of both seminal vesicles are blocked, an acidic reaction of the sperm is observed (acidity 6.0–6.8 pH). The fertilizing ability of such sperm is reduced. In an acidic environment, sperm lose motility and die. If the acidity of the seminal fluid becomes less than 6.0 pH, the sperm completely lose their motility and die. Skin acidity The surface of the skin is covered with water-lipid acid mantle or Marcionini's mantle, consisting of a mixture of sebum and sweat, to which organic acids are added - lactic, citric and others, formed as a result of biochemical processes occurring in the epidermis. The acidic water-lipid mantle of the skin is the first barrier of protection against microorganisms. For most people, the normal acidity of the mantle is 3.5–6.7 pH. The bactericidal property of the skin, which gives it the ability to resist microbial invasion, is due to the acidic reaction of keratin, the peculiar chemical composition of sebum and sweat, and the presence on its surface of a protective water-lipid mantle with a high concentration of hydrogen ions. The low molecular weight fatty acids it contains, primarily glycophospholipids and free fatty acids, have a bacteriostatic effect that is selective for pathogenic microorganisms. The surface of the skin is populated by normal symbiotic microflora, capable of existing in an acidic environment: Staphylococcus epidermidis, Staphylococcus aureus, Propionibacterium acnes and others. Some of these bacteria themselves produce lactic and other acids, contributing to the formation of the skin's acid mantle. The upper layer of the epidermis (keratin scales) is acidic with a pH value of 5.0 to 6.0. In some skin diseases, the acidity level changes. For example, with fungal diseases the pH increases to 6, with eczema to 6.5, with acne to 7. Acidity of other human biological fluids The acidity of fluids inside the human body normally coincides with the acidity of the blood and ranges from 7.35 to 7.45 pH. The normal acidity of some other human biological fluids is shown in the table: In the photo on the right: buffer solutions with pH=1.2 and pH=9.18 for calibration

  pH value- this is a hydrogen indicator, thanks to which you can determine how many free hydrogen ions are contained in an aqueous solution. When various salts are dissolved in water, or, for example, when preparing a certain solution, the acid-base balance is disturbed, after which it is necessary measure pH.

  However, one should not confuse the parameters that determine the alkalinity and acidity of the solution with pH indicator, since there is some difference between them, but many still do not notice this difference. pH value in fact, it determines the level of alkalinity and acidity of the solution, but the acidity and alkalinity of the solution already indicate the number of compounds contained in the solution and helping to neutralize the alkali or acid.

  
  The speed of chemical reactions directly depends on the pH level.

  In the field of hydroponics applications pH control quite important. pH influence affects plant development both positively and negatively. Since its uncontrolled change in any direction can lead to a lot of problems, and even to the death of the plant, which often happens.

  In everyday life pH concentration must be maintained within limits so that it does not affect water quality. Thus, drinking water is characterized by pH level 6-9, in turn, for solutions that are used in hydroponics, it usually ranges from 5.5 to 7.5.

  Is there a need for systematic determining pH?

  pH of aqueous solutions- plays a major role in determining the performance and properties of a hydroponic solution. After all, at an optimal pH level, plants easily absorb nutrients, which is so necessary for successful development and growth.

  It is worth noting that at reduced acidity pH the solution acquires an unpleasant feature - corrosive activity. When the level pH increased pH>11, the solution has an unpleasant odor. It must be handled with particular care, as it can irritate the skin and eyes of a person.

  It should also be clarified that there are no ideal and constant pH indicators. For certain types of plants it should be about 6.8 - 7.5, and for other crops - about 5.5 - 6.8.

  pH control methods

  There are several fairly common methods of control pH factor a: pH measurement using universal indicators: pH meter, stripspH, .

  According to some experts, this measurement method, such as strips, looks somewhat rough pH test. It consists in the use of universal indicators, which are a mixture of several strips using dyes, the color of which depends directly on the acid-base environment: from red, slightly touching yellow, then green, blue and finally reaching purple. This kind of coloring occurs as a result of a transition from an acidic region to an alkaline region. No matter how universal this control method is, it has one significant drawback: ph environment changes significantly if, for example, the solution has some color or is cloudy.

  If, as a control method pH of aqueous solutions you choosed electronic ph meter(for example, or , in this case you can measure pH level in the range from 0.01 to 14. As a result, you will get more accurate information than if you used indicators.

  The function of this pH device is based on measurements of the EMF of a galvanic circuit, which in its design has a glass electrode, the potential of which depends directly on the concentrated content of H+ ions in a particular solution. This method is very convenient, since the accuracy of the device directly depends on timely calibration. With this method it is quite easy determine the pH of the solution in conditions of its turbidity or coloring. Actually, thanks to this, this method is one of the most popular.

  pH adjustment

  To lower or increase the acidity of a hydroponic solution, use special pH lowering or pH increasing solutions. Be careful, it only takes a few drops per liter to change the solution.

  
  

  Using pH Down and pH Up:

  To shift the pH up or down, special solutions are used.

  At the rate of 3 ml per 10 liters for a shift of 1 point up or down.

  For example, your water pH is 4.0, and you need to raise it to 5.5. The following calculation is made:

  5.5-4.0=1.5x3=4.5 ml pH UP per 10 liters of water.

  The calculation is similar for pH DOWN

  What is tds?

  TDS, ppM, or pH of salts - the total content of salts in a solution

  It is worth touching on the topic of mineralization. A process such as mineralization is the determination of the total amount of salts contained in a solution. Among the most common, inorganic salts should be noted. They can be chlorides, bicarbonates, sulfates of potassium, calcium, sodium, magnesium; it can also be a minimum number of organic compounds that dissolve in water.

  In everyday understanding, this is the level of hardness and softness of water.

  MeasurementTDS

  The easiest way to measure salt levels is to purchase salinity meter- . This device determines the ppm of a solution in a matter of seconds.

  In Europe, mineralization is usually called in two ways: and Total Dissolved Solids ( TDS). This will be translated into Russian as the number of dissolved particles. The unit for determining the level of mineralization is 1 mg/liter. This is an equivalent parameter for the weight of all dissolved particles and elements in milligrams, namely salts, which are contained in a liter of solution.

  The mineralization expression level can also be displayed in ppM. This abbreviation stands for parts per million, which translated into Russian means “parts per million,” that is, how many salt particles are dissolved in 1 million particles of an aqueous solution. A similar abbreviation can be found in some European sources. It looks like this: 1 mg/l = 1 ppm.

  ppM to EC conversion table.

  (more precisely, hydronium cations) in natural waters is determined, as a rule, by the quantitative ratio of the concentrations of carbonic acid and its ions.

  CO2 + H2O ↔ H+ + HCO3- ↔ 2H+ + CO32-

  For convenience of expressing the content of hydrogen ions, a value was used that is the logarithm of their concentration, taken with the opposite sign:

  pH = - lg.

  Surface waters containing small amounts of carbon dioxide are characterized by an alkaline reaction. Changes in pH are closely related to photosynthetic processes (due to the consumption of CO2 by aquatic vegetation). Humic acids present in soils are also a source of hydrogen ions. Hydrolysis of heavy metal salts plays a role in cases where significant amounts of iron, aluminum, copper and other metal sulfates enter the water:

  Fe2+ ​​+ 2H2O → Fe(OH)2 + 2H+

  The pH value of water is one of the most important indicators of water quality. The concentration of hydrogen ions is of great importance for the chemical and biological processes occurring in natural waters. The development and vital activity of aquatic plants, the stability of various forms of migration of elements, and the aggressive effect of water on metals and concrete depend on the pH value. The pH of water also affects the processes of transformation of various forms of nutrients and changes the toxicity of pollutants. In an open reservoir, several stages of the acidification process can be distinguished:

  at the first stage, the pH practically does not change (bicarbonate ions manage to completely neutralize H+ ions). This continues until the total alkalinity in the reservoir drops by about 10 times to a value of less than 0.1 mol/dm3. At the second stage of acidification of the reservoir, the pH of the water usually does not rise above 5.5 throughout the year. Such reservoirs are said to be moderately acidic. At this stage of acidification, significant changes occur in the species composition of living organisms. at the third stage of acidification, the pH of water bodies stabilizes at pH values<5 (обычно рН=4,5), даже если атмосферные осадки имеют более высокие значения рН. Это связано с присутствием гумусовых веществ и соединений алюминия в водоемах и почвенном слое.

  The pH value in river waters usually varies between 6.5-8.5: in precipitation 4.6-6.1, in swamps 5.5-6.0, in sea waters 7.9-8.3. At the same time, the nonconcentration of hydrogen ions is subject to seasonal fluctuations. In winter, the pH value for most river waters is 6.8-7.4, in summer 7.4-8.2. The pH of natural waters is determined to some extent by the geology of the drainage basin. In accordance with the requirements for the composition and properties of water in reservoirs near drinking water use points, water in water bodies in recreation areas, as well as water in fishery reservoirs, the pH value should not go beyond the range of 6.5-8.5.

  Depending on the pH value, natural waters can be rationally divided into seven groups :

  strongly acidic waters		the result of hydrolysis of heavy metal salts (mine and mine waters)
  acidic waters		the entry of carbonic acid, fulvic acids and other organic acids into water as a result of the decomposition of organic substances
  slightly acidic waters		the presence of humic acids in soil and swamp waters (waters of the forest zone)
  neutral waters	pH = 6.5...7.5	presence of Ca(HCO3)2, Mg(HCO3)2 in waters
  slightly alkaline waters	pH = 7.5...8.5
  alkaline waters	pH = 8.5...9.5	presence of Na2CO3 or NaHCO3
  highly alkaline waters

  Redox potential (Eh) - Red-Ox potential

  A measure of the chemical activity of elements or their compounds in reversible chemical processes associated with a change in the charge of ions in solutions. Redox potentials are expressed in volts (millivolts). The redox potential of any reversible system is determined by the formula

  Eh = E0 + (0.0581/n) log(Ox/Red) at t = 20°С

  Where Eh- redox potential of the environment;
  E0- normal redox potential, at which the concentrations of the oxidized and reduced forms are equal;
  Ox- concentration of the oxidized form;
  Red- concentration of the reduced form;
  n- the number of electrons participating in the process.

  In natural water, the Eh value ranges from - 400 to + 700 mV, is determined by the entire set of oxidative and reduction processes occurring in it and, under equilibrium conditions, characterizes the environment immediately relative to all elements having variable valence. The study of redox potential makes it possible to identify natural environments in which the existence of chemical elements with variable valency in a certain form is possible, as well as to identify conditions under which migration of metals is possible. There are several main types of geochemical environments in natural waters:

  oxidative - characterized by the values ​​of Еh > + (mV, the presence of free oxygen, as well as a number of elements in the highest form of their valency (Fe3+, Mo6+, As5-, V5+, U6+, Sr4+, Cu2+, Pb2+); transitional redox - determined by the values Eh + (100-0) mV, unstable geochemical regime and variable content of hydrogen sulfide and oxygen. Under these conditions, both weak oxidation and weak reduction of a number of metals occur - characterized by Eh values.< 0. В подземных водах присутствуют металлы низких степеней валентности (Fe2+, Mn2+, Mo4+, V4+, U4+), а также сероводород.

  The value of the Red-Ox potential of water (Eh) and the pH value are interrelated.

  Acidity

  Acidity is the content of substances in water that react with hydroxyl ions. Hydroxide flow reflects the overall acidity of the water. In ordinary natural waters, acidity in most cases depends only on the content of free carbon dioxide. The natural part of acidity is also created by humic and other weak organic acids and cations of weak bases (ammonium ions, iron, aluminum, organic bases). In these cases, the pH of the water does not fall below 4.5.

  Polluted water bodies may contain large amounts of strong acids or their salts due to the discharge of industrial wastewater. In these cases the pH may be below 4.5. Part of the total acidity that reduces pH to values< 4,5, называется свободной.

  Alkalinity

  The alkalinity of natural or purified waters refers to the ability of some of their components to bind an equivalent amount of strong acids. Alkalinity is due to the presence of weak acid anions in water (carbonates, bicarbonates, silicates, borates, sulfites, hydrosulfites, sulfides, hydrosulfides, humic acid anions, phosphates) - their sum is called total alkalinity. Due to the insignificant concentration of the last three ions, the total alkalinity of water is usually determined only by carbonic acid anions (carbonate alkalinity). Anions, when hydrolyzed, form hydroxyl ions:

  CO32- + H2O ↔ HCO3- + OH-;

  HCO3- + H2O ↔ H2CO3 + OH-.

  Alkalinity is determined by the amount of strong acid required to neutralize 1 dm3 of water. The alkalinity of most natural waters is determined only by calcium and magnesium bicarbonates; the pH of these waters does not exceed 8.3. Determination of alkalinity is useful in the dosing of chemicals needed in the treatment of water supplies, as well as in the reagent treatment of some wastewater. Determination of alkalinity in excess concentrations of alkaline earth metals is important in determining the suitability of water for irrigation. Together with pH values, water alkalinity serves to calculate the carbonate content and carbonic acid balance in water.

  Oxygen saturation degree

  The relative content of oxygen in water, expressed as a percentage of its normal content. Depends on water temperature, atmospheric pressure and salinity. Calculated by the formula

  M = (A×101308×100)/N×P,

  Where M- degree of water saturation with oxygen, %;
  A- oxygen concentration, mg/dm3;
  R- atmospheric pressure in a given area, Pa.
  N- normal oxygen concentration at a given temperature, salinity (salinity) and total pressure 101308 Pa.