The hydrogen index - pH - is a measure of the activity (in the case of dilute solutions it reflects the concentration) of hydrogen ions in a solution, quantitatively expressing its acidity, calculated as a negative (taken with the opposite sign) decimal logarithm of the activity of hydrogen ions, expressed in moles per liter.
pH = – lg
This concept was introduced in 1909 by the Danish chemist Sorensen. The indicator is called pH, after the first letters of the Latin words potentia hydrogeni - the strength of hydrogen, or pondus hydrogenii - the weight of hydrogen.
The reciprocal pH value has become somewhat less widespread - an indicator of the basicity of the solution, pOH, equal to the negative decimal logarithm of the concentration in the solution of OH ions:
pOH = – lg
In pure water at 25 ° C, the concentrations of hydrogen ions () and hydroxide ions () are the same and amount to 10 -7 mol / l, this directly follows from the water autoprotolysis constant K w, which is otherwise called the ion product of water:
K w \u003d \u003d 10 -14 [mol 2 / l 2] (at 25 ° C)
pH + pOH = 14
When the concentrations of both types of ions in a solution are the same, the solution is said to be neutral. When an acid is added to water, the concentration of hydrogen ions increases, and the concentration of hydroxide ions decreases accordingly, 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 the solution is acidic, and when > - alkaline.
pH determination
Several methods are widely used to determine the pH value of solutions.
1) The pH value can be approximated with indicators, accurately measured with a pH meter, or determined analytically by performing an acid-base titration.
For a rough estimate of the concentration of hydrogen ions, acid-base indicators are widely used - organic dye substances, the color of which depends on the pH of the medium. The most famous 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 acidity range, usually 1-2 units (see Table 1, lesson 2).
To extend the working range of pH measurement, the so-called universal indicator is used, which is a mixture of several indicators. The universal indicator consistently changes color from red through yellow, green, blue to purple when moving from an acidic to an alkaline region. Determination of pH by the indicator method is difficult for cloudy or colored solutions.
2) The analytical volumetric method - acid-base titration - also gives accurate results for determining the total acidity of solutions. A solution of known concentration (titrant) is added dropwise to the test solution. When they are mixed, a chemical reaction takes place. The equivalence point - the moment when the titrant is exactly enough to completely complete the reaction - is fixed using an indicator. Further, knowing the concentration and volume of the added titrant solution, the total acidity of the solution is calculated.
The acidity of the environment is important for many chemical processes, and the possibility of the occurrence or the result 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 that allow you to maintain a practically 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 (Table 2).
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, maintaining acid-base homeostasis is a task of exceptional importance for the normal functioning of the body. Dynamic maintenance of the optimal pH of biological fluids is achieved through the action of buffer systems.
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, is convenient and highly accurate, allows you to measure the pH of opaque and colored solutions and therefore widely used.
Using a pH meter, the concentration of hydrogen ions (pH) is measured in solutions, drinking water, food products and raw materials, environmental objects and production systems for continuous monitoring of technological processes, including in aggressive environments.
A pH meter is indispensable for hardware monitoring of the pH of uranium and plutonium separation solutions, when the requirements for the correctness of equipment readings without its calibration are extremely high.
The device can be used in stationary and mobile laboratories, including field laboratories, as well as clinical diagnostic, forensic, research, industrial, including meat and dairy and baking industries.
Recently, pH meters have also been widely used in aquarium farms, household water quality control, agriculture (especially in hydroponics), and also for monitoring health diagnostics.
Table 2. pH values for some biological systems and other solutions
Hydrogen indicator, pH(lat. pondus hydrogenii- "weight of hydrogen", pronounced "pash") is a measure of the activity (in highly dilute solutions, equivalent to the concentration) of hydrogen ions in a solution, which quantitatively expresses its acidity. Equal in modulus and opposite in sign to the decimal logarithm of the activity of hydrogen ions, which is expressed in moles per liter:
History of pH.
concept pH introduced by the Danish chemist Sorensen in 1909. The indicator is called pH (according to the first letters of Latin words potentia hydrogeni is the strength of hydrogen, or pondus hydrogeni is the weight of hydrogen). In chemistry, the combination pX usually denote a value that is equal to lg X, but with a letter H in this case denote the concentration of hydrogen ions ( H+), or rather, the thermodynamic activity of hydronium ions.
Equations relating pH and pOH.
pH value output.
In pure water at 25 °C, the concentration of hydrogen ions ([ H+]) and hydroxide ions ([ Oh− ]) are the same and equal to 10 −7 mol/l, this clearly follows from the definition of the ionic product of water, equal to [ H+] · [ Oh− ] and is equal to 10 −14 mol²/l² (at 25 °C).
If the concentrations of two types of ions in a solution are the same, then it is said that the solution has a neutral reaction. When an acid is added to water, the concentration of hydrogen ions increases, and the concentration of hydroxide ions decreases; when a base is added, on the contrary, the content of hydroxide ions increases, and the concentration of hydrogen ions decreases. When [ H+] > [Oh− ] it is said that the solution is acidic, and when [ Oh − ] > [H+] - alkaline.
To make it more convenient to represent, to get rid of the negative exponent, instead of the concentrations of hydrogen ions, their decimal logarithm is used, which is taken with the opposite sign, which is the hydrogen exponent - pH.
Basicity index of a solution pOH.
Slightly less popular is the reverse pH value - solution basicity index, pOH, which is equal to the decimal logarithm (negative) of the concentration in the solution of ions Oh − :
as in any aqueous solution at 25 ° C, then at this temperature:
pH values in solutions of different acidity.
- Contrary to popular belief, pH can vary except for the interval 0 - 14, it can also go beyond these limits. For example, at a concentration of hydrogen ions [ H+] = 10 −15 mol/l, pH= 15, at a concentration of hydroxide ions of 10 mol / l pOH = −1 .
Because at 25 °C (standard conditions) [ H+] [Oh − ] = 10 −14 , it is clear that at this temperature pH + pOH = 14.
Because in acidic solutions [ H+] > 10 −7 , which means that for acidic solutions pH < 7, соответственно, у щелочных растворов pH > 7 , pH neutral solutions is 7. At higher temperatures, the electrolytic dissociation constant of water increases, which means that the ion product of water increases, then it will be neutral pH= 7 (which corresponds to simultaneously increased concentrations as H+, and Oh−); with decreasing temperature, on the contrary, neutral pH increases.
Methods for determining the pH value.
There are several methods for determining the value pH solutions. The pH value is approximately estimated using indicators, accurately measured using pH-meter or determined analytically by conducting acid-base titration.
- For a rough estimate of the concentration of hydrogen ions, one often uses acid-base indicators- organic dyes, the color of which depends on pH environment. The most popular indicators are: litmus, phenolphthalein, methyl orange (methyl orange), etc. Indicators can be in 2 differently colored forms - either acidic or basic. The color change of all indicators occurs in their acidity range, often 1-2 units.
- To increase the working measurement interval pH apply universal indicator, which is a mixture of several indicators. The universal indicator consistently changes color from red through yellow, green, blue to purple when moving from an acidic to an alkaline region. Definitions pH indicator method is difficult for cloudy or colored solutions.
- The use of a special device - pH-meter - makes it possible to measure pH over a wider range and more accurately (up to 0.01 units pH) than with indicators. Ionometric method of determination pH is based on the measurement of the EMF of a galvanic circuit with a millivoltmeter-ionometer, which includes a glass electrode, the potential of which depends on the concentration of ions H+ in the surrounding solution. The method has high accuracy and convenience, especially after calibration of the indicator electrode in the selected range pH, which makes it possible to measure pH opaque and colored solutions and is therefore often used.
- Analytical volumetric method — acid-base titration- also gives accurate results for determining the acidity of solutions. A solution of known concentration (titrant) is added dropwise to the solution to be tested. When they are mixed, a chemical reaction occurs. The equivalence point - the moment when the titrant is exactly enough to complete the reaction - is fixed using an indicator. After that, if the concentration and volume of the added titrant solution are known, the acidity of the solution is determined.
- pH:
0.001 mol/L HCl at 20 °C has pH=3, at 30 °C pH=3,
0.001 mol/L NaOH at 20 °C has pH=11.73, at 30 °C pH=10.83,
Influence of temperature on values pH explain the different dissociation of hydrogen ions (H +) and is not an experimental error. Temperature effect cannot be compensated electronically pH-meter.
The role of pH in chemistry and biology.
The acidity of the environment is important for most chemical processes, and the possibility of occurrence or the result of a particular reaction often depends on pH environment. To maintain a certain value pH in the reaction system during laboratory studies or in production, buffer solutions are used to maintain an almost constant value pH when diluted or when small amounts of acid or alkali are added to the solution.
Hydrogen indicator pH often used to characterize the acid-base properties of various biological media.
For biochemical reactions, the acidity of the reaction medium occurring in living systems is of great importance. The concentration of hydrogen ions in a solution often affects the physicochemical properties and biological activity of proteins and nucleic acids; therefore, maintaining acid-base homeostasis is a task of exceptional importance for the normal functioning of the body. Dynamic maintenance of optimal pH biological fluids is achieved under the action of buffer systems of the body.
In the human body in different organs, the pH value is different.
|
Some Meanings pH. |
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Substance |
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electrolyte in lead batteries |
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Gastric juice |
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Lemon juice (5% citric acid solution) |
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food vinegar |
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Coca Cola |
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Apple juice |
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Skin of a healthy person |
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Acid rain |
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Drinking water |
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Pure water at 25°C |
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Sea water |
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Soap (fatty) for hands |
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Ammonia |
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Bleach (bleach) |
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Concentrated alkali solutions |
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The tissues of a living organism are very sensitive to fluctuations in pH - outside the allowable range, proteins are denatured: cells are destroyed, enzymes lose their ability to perform their functions, the body may die
What is pH (hydrogen index) and acid-base balance
The ratio of acid and alkali in any solution is called acid-base balance.(ABR), although physiologists believe that it is more correct to call this ratio the acid-base state.
KShchr is characterized by a special indicator pH(power Hydrogen - "power of hydrogen"), which shows the number of hydrogen atoms in a given solution. At a pH of 7.0, one speaks of a neutral environment.
The lower the pH level, the more acidic the environment (from 6.9 to O).
An alkaline environment has a high pH level (from 7.1 to 14.0).
The human body is 70% water, so water is one of its most important constituents. T atea person has a certain acid-base ratio, characterized by pH (hydrogen) index.
The pH value depends on the ratio between positively charged ions (forming an acidic environment) and negatively charged ions (forming an alkaline environment).
The body constantly strives to balance this ratio, maintaining a strictly defined pH level. When the balance is disturbed, many serious diseases can occur.
Keep the right pH balance for good health
The body is able to properly absorb and store minerals and nutrients only at the proper level of acid-base balance. The tissues of a living organism are very sensitive to fluctuations in pH - outside the permissible range, proteins are denatured: cells are destroyed, enzymes lose their ability to perform their functions, and the body may die. Therefore, the acid-base balance in the body is tightly regulated.
Our body uses hydrochloric acid to break down food. In the process of vital activity of the body, both acidic and alkaline decay products are required., and the first is formed more than the second. Therefore, the body's defense systems, which ensure the invariability of its ASC, are "tuned" primarily to neutralize and excrete, first of all, acidic decay products.
Blood has a slightly alkaline reaction: The pH of arterial blood is 7.4, and that of venous blood is 7.35 (due to excess CO2).
A pH shift of at least 0.1 can lead to severe pathology.
With a shift in blood pH by 0.2, a coma develops, by 0.3, a person dies.
The body has different levels of PH
Saliva - predominantly alkaline reaction (pH fluctuation 6.0 - 7.9)
Typically, the acidity of mixed human saliva is 6.8–7.4 pH, but at a high rate of salivation it reaches 7.8 pH. The acidity of the saliva of the parotid glands is 5.81 pH, the submandibular glands - 6.39 pH. In children, the average acidity of mixed saliva is 7.32 pH, in adults - 6.40 pH (Rimarchuk G.V. and others). The acid-base balance of saliva, in turn, is determined by a similar balance in the blood, which nourishes the salivary glands.
Esophagus - Normal acidity in the esophagus is 6.0–7.0 pH.
Liver - the reaction of cystic bile is close to neutral (pH 6.5 - 6.8), the reaction of hepatic bile is alkaline (pH 7.3 - 8.2)
Stomach - sharply acidic (at the height of digestion pH 1.8 - 3.0)
The maximum theoretically possible acidity in the stomach is 0.86 pH, which corresponds to acid production of 160 mmol/l. The minimum theoretically possible 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. Acidity in the depth 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.
It is a common misconception that the main problem for a person is the increased acidity of the stomach. From her heartburn and ulcers.
In fact, a much bigger problem is the low acidity of the stomach, which occurs many times more often.
The main cause of heartburn in 95% is not an excess, but a lack of hydrochloric acid in the stomach.
The lack of hydrochloric acid creates ideal conditions for the colonization of the intestinal tract by various bacteria, protozoa and worms.
The insidiousness of the situation is that the low acidity of the stomach "behaves quietly" and goes unnoticed by a person.
Here is a list of signs that make it possible to suspect a decrease in stomach acid.
- Discomfort in stomach after eating.
- Nausea after taking medication.
- Flatulence in the small intestine.
- Loose stools or constipation.
- Undigested food particles in the stool.
- Itching around the anus.
- Multiple food allergies.
- Dysbacteriosis or candidiasis.
- Dilated blood vessels on the cheeks and nose.
- Acne.
- Weak, peeling nails.
- Anemia due to poor absorption of iron.
Of course, an accurate diagnosis of low acidity requires determining the pH of gastric juice.(for this you need to contact a gastroenterologist).
When acidity is increased, there are a lot of drugs to reduce it.
In the case of low acidity, there are very few effective remedies.
As a rule, preparations of hydrochloric acid or vegetable bitterness are used, stimulating the separation of gastric juice (wormwood, calamus, peppermint, fennel, etc.).
Pancreas - pancreatic juice is slightly alkaline (pH 7.5 - 8.0)
Small intestine - alkaline (pH 8.0)
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 the juice of the small intestine is 7.2–7.5 pH. With increased secretion, it reaches 8.6 pH. The acidity of the secretion of the duodenal glands - from pH 7 to 8 pH.
Large intestine - slightly acidic (5.8 - 6.5 pH)
This is a weakly acidic environment, which is maintained by normal microflora, in particular, bifidobacteria, lactobacilli and propionobacteria due to the fact that they neutralize alkaline metabolic products and produce their acidic metabolites - lactic acid and other organic acids. By producing organic acids and lowering the pH of the intestinal contents, the normal microflora creates conditions under which pathogenic and opportunistic microorganisms cannot multiply. That is why streptococci, staphylococci, klebsiella, clostridia fungi and other “bad” bacteria make up only 1% of the entire intestinal microflora of a healthy person.
Urine - predominantly slightly acidic (pH 4.5-8)
When eating with animal proteins containing sulfur and phosphorus, acid urine is mainly excreted (pH less than 5); in the final urine there is a significant amount of inorganic sulfates and phosphates. If the food is mainly dairy or vegetable, then the urine tends to be alkalized (pH over 7). The renal tubules play a significant role in maintaining acid-base balance. Acidic urine will be excreted in all conditions leading to metabolic or respiratory acidosis as the kidneys compensate for shifts in acid-base balance.
Skin - slightly acid reaction (pH 4-6)
If the skin is prone to oiliness, the pH value may approach 5.5. And if the skin is very dry, the pH can be as high as 4.4.
The bactericidal property of the skin, which gives it the ability to resist microbial invasion, is due to the acid reaction of keratin, the peculiar chemical composition of sebum and sweat, and the presence of a protective water-lipid mantle with a high concentration of hydrogen ions on its surface. The low molecular weight fatty acids included in its composition, primarily glycophospholipids and free fatty acids, have a bacteriostatic effect that is selective for pathogenic microorganisms.
Sex organs
The normal acidity of a woman's vagina ranges from 3.8 to 4.4 pH and averages between 4.0 and 4.2 pH.
At birth, a girl's vagina is sterile. Then, within a few days, it is populated by a variety of bacteria, mainly staphylococci, streptococci, anaerobes (that is, bacteria that do not require oxygen to live). Before the onset of menstruation, the acidity level (pH) of the vagina is close to neutral (7.0). But during puberty, the walls of the vagina thicken (under the influence of estrogen - one of the female sex hormones), the pH drops to 4.4 (i.e., the acidity increases), which causes changes in the vaginal flora.
The uterine cavity is normally sterile, and lactobacilli that inhabit the vagina and maintain the high acidity of its environment prevent the entry of pathogens into it. If for some reason the acidity of the vagina shifts towards alkaline, the number of lactobacilli drops sharply, and in their place other microbes develop that can enter the uterus and lead to inflammation, and then to problems with pregnancy.
Sperm
The normal level of semen acidity is between 7.2 and 8.0 pH. An increase in the pH level of sperm occurs during an infectious process. A sharply alkaline reaction of sperm (acidity of about 9.0–10.0 pH) indicates a pathology of the prostate gland. With blockage of the excretory ducts of both seminal vesicles, an acid reaction of sperm is noted (acidity 6.0-6.8 pH). The fertilizing ability of such sperm is reduced. In an acidic environment, spermatozoa lose their mobility and die. If the acidity of the seminal fluid becomes less than 6.0 pH, the spermatozoa completely lose their mobility and die.
Cells and interstitial fluid
In the cells of the body, the pH value is about 7, in the extracellular fluid - 7.4. Nerve endings that are outside the cells are very sensitive to changes in pH. With mechanical or thermal damage to tissues, the cell walls are destroyed and their contents enter the nerve endings. As a result, the person feels pain.
Scandinavian researcher Olaf Lindal did the following experiment: using a special needleless injector, a very thin stream of a solution was injected through the skin of a person, which did not damage the cells, but acted on the nerve endings. It was shown that it is hydrogen cations that cause pain, and with a decrease in the pH of the solution, the pain intensifies.
Similarly, a solution of formic acid directly "acts on the nerves", which is injected under the skin by stinging insects or nettles. The different pH values of tissues also explain why a person feels pain in some inflammations, and not in others.
Interestingly, injecting pure water under the skin caused particularly severe pain. This phenomenon, strange at first glance, is explained as follows: cells, upon contact with pure water, rupture as a result of osmotic pressure and their contents act on the nerve endings.
Table 1. Hydrogen indicators for solutions
|
Solution |
RN |
|
HCl |
1,0 |
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H2SO4 |
1,2 |
|
H 2 C 2 O 4 |
1,3 |
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NaHSO4 |
1,4 |
|
H 3 RO 4 |
1,5 |
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Gastric juice |
1,6 |
|
Wine acid |
2,0 |
|
Lemon acid |
2,1 |
|
HNO 2 |
2,2 |
|
Lemon juice |
2,3 |
|
Lactic acid |
2,4 |
|
Salicylic acid |
2,4 |
|
table vinegar |
3,0 |
|
grapefruit juice |
3,2 |
|
CO 2 |
3,7 |
|
Apple juice |
3,8 |
|
H 2 S |
4,1 |
|
Urine |
4,8-7,5 |
|
Black coffee |
5,0 |
|
Saliva |
7,4-8 |
|
Milk |
6,7 |
|
Blood |
7,35-7,45 |
|
Bile |
7,8-8,6 |
|
ocean water |
7,9-8,4 |
|
Fe(OH)2 |
9,5 |
|
MgO |
10,0 |
|
Mg(OH)2 |
10,5 |
|
Na2CO3 |
|
|
Ca(OH)2 |
11,5 |
|
NaOH |
13,0 |
Fish eggs and fry are especially sensitive to changes in the pH of the medium. The table allows a number of interesting observations to be made. pH values, for example, immediately show the comparative strength of acids and bases. A strong change in the neutral medium is also clearly visible as a result of the hydrolysis of salts formed by weak acids and bases, as well as during the dissociation of acid salts.
Urine pH is not a good indicator of overall body pH, and it is not a good indicator of overall health.
In other words, no matter what you eat and at any urine pH, you can be absolutely sure that your arterial blood pH will always be around 7.4.
When a person consumes, for example, acidic foods or animal protein, under the influence of buffer systems, the pH shifts to the acid side (becomes less than 7), and when, for example, mineral water or plant foods are consumed, it shifts to alkaline (becomes more than 7). Buffer systems keep the pH in the acceptable range for the body.
By the way, doctors say that we tolerate the shift to the acid side (the same acidosis) much easier than the shift to the alkaline side (alkalosis).
It is impossible to shift the pH of the blood by any external influence.
THE MAIN MECHANISMS OF BLOOD PH MAINTENANCE ARE:
1. Buffer systems of blood (carbonate, phosphate, protein, hemoglobin)
This mechanism operates very quickly (fractions of a second) and therefore belongs to the rapid mechanisms for regulating the stability of the internal environment.
Bicarbonate blood buffer quite powerful and most mobile.
One of the important buffers of blood and other body fluids is the bicarbonate buffer system (HCO3/CO2): CO2 + H2O ⇄ HCO3- + H+ The main function of the blood bicarbonate buffer system is the neutralization of H+ ions. This buffer system plays a particularly important role because the concentrations of both buffer components can be adjusted independently of each other; [CO2] - by breathing, - in the liver and kidneys. Thus, it is an open buffer system.
The hemoglobin buffer system is the most powerful.
It accounts for more than half of the buffer capacity of the blood. The buffer properties of hemoglobin are due to the ratio of reduced hemoglobin (HHb) and its potassium salt (KHb).
Plasma proteins due to the ability of amino acids to ionization, they also perform a buffer function (about 7% of the buffer capacity of blood). In an acidic environment, they behave like acid-binding bases.
Phosphate buffer system(about 5% of the buffer capacity of the blood) is formed by inorganic blood phosphates. Acid properties are shown by monobasic phosphate (NaH 2 P0 4), and bases - by dibasic phosphate (Na 2 HP0 4). They function on the same principle as bicarbonates. However, due to the low content of phosphates in the blood, the capacity of this system is small.
2. Respiratory (pulmonary) system of regulation.
Due to the ease with which the lungs regulate CO2 concentration, this system has a significant buffering capacity. Removal of excess amounts of CO 2 , regeneration of bicarbonate and hemoglobin buffer systems are carried out easily.
At rest, a person emits 230 ml of carbon dioxide per minute, or about 15,000 mmol per day. When carbon dioxide is removed from the blood, an approximately equivalent amount of hydrogen ions disappears. Therefore, breathing plays an important role in maintaining the acid-base balance. So, if the acidity of the blood increases, then an increase in the content of hydrogen ions leads to an increase in pulmonary ventilation (hyperventilation), while carbon dioxide molecules are excreted in large quantities and the pH returns to normal levels.
An increase in the content of bases is accompanied by hypoventilation, resulting in an increase in the concentration of carbon dioxide in the blood and, accordingly, the concentration of hydrogen ions, and the shift in the reaction of the blood to the alkaline side is partially or completely compensated.
Consequently, the external respiration system is quite quickly (within a few minutes) able to eliminate or reduce pH shifts and prevent the development of acidosis or alkalosis: an increase in lung ventilation by 2 times increases blood pH by about 0.2; reducing ventilation by 25% can reduce the pH by 0.3-0.4.
3. Renal (excretory system)
Acts very slowly (10-12 hours). But this mechanism is the most powerful and is able to completely restore the pH of the body by removing urine with alkaline or acidic pH values. The participation of the kidneys in maintaining acid-base balance consists in removing hydrogen ions from the body, reabsorbing bicarbonate from the tubular fluid, synthesizing bicarbonate in case of its deficiency and removal in excess.
The main mechanisms for reducing or eliminating shifts in blood acid-base balance realized by kidney nephrons include acidogenesis, ammoniogenesis, phosphate secretion, and K+,Ka+-exchange mechanism.
The mechanism of blood pH regulation in the whole organism consists in the joint action of external respiration, blood circulation, excretion and buffer systems. So, if as a result of the increased formation of H 2 CO 3 or other acids, excess anions appear, they are first neutralized by buffer systems. In parallel, breathing and blood circulation are intensified, which leads to an increase in the release of carbon dioxide by the lungs. Non-volatile acids, in turn, are excreted in the urine or sweat.
Normally, blood pH can change only for a short time. Naturally, with damage to the lungs or kidneys, the body's functional capabilities to maintain pH at the proper level are reduced. If a large amount of acidic or basic ions appears in the blood, only buffer mechanisms (without the help of excretion systems) will not keep the pH at a constant level. This leads to acidosis or alkalosis. published
© Olga Butakova "Acid-base balance is the basis of life"
Story
Equations relating pH and pOH
pH value output
In pure water at 25 ° 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 ion product of water, which is equal to and is 10 -14 mol² / l² (at 25°C).
When the concentrations of both types of ions in a solution are the same, 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 decreases accordingly, when a base is added, on the contrary, the content of hydroxide ions increases, and the concentration of hydrogen ions decreases. When > say that the solution is sour, and for > - alkaline.
For convenience of presentation, in order to get rid of the negative exponent, instead of the concentrations of hydrogen ions, their decimal logarithm, taken with the opposite sign, is used, which is actually the hydrogen indicator - pH).
pOH
The reciprocal pH value has become somewhat less widespread - an indicator of the basicity of the solution, pOH, equal to the negative decimal logarithm of the concentration in the solution of OH - ions:
as in any aqueous solution at 22 ° C \u003d 1.0 × 10 - 14, it is obvious that at this temperature:
pH values in solutions of different 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 concentration of hydrogen ions = 10 -15 mol / l, pH = 15, at a concentration of hydroxide ions of 10 mol / l pOH = -1.
|
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 pH< 7, аналогично pH щелочных растворов pH >7, the pH of neutral solutions is 7. At higher temperatures, the dissociation constant of water increases, and the ion product of water increases accordingly, so pH is neutral.< 7 (что соответствует одновременно возросшим концентрациям как H + , так и OH -); при понижении температуры, напротив, нейтральная pH возрастает.
Methods for determining the pH value
Several methods are widely used to determine the pH value of solutions. The pH value can be approximated with indicators, accurately measured with a pH meter, or determined analytically by performing an acid-base titration.
- For a rough estimate of the concentration of hydrogen ions, acid-base indicators are widely used - organic dye substances, the color of which depends on the pH of the medium. The most famous 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 acidity range, usually 1-2 units.
To extend the working range of pH measurement, the 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 purple when moving from an acidic to an alkaline region. Determination of pH by the indicator method is difficult for cloudy or colored solutions.
- 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 with 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 measuring the pH of opaque and colored solutions and is therefore widely used.
- Analytical volumetric method - acid-base titration - also gives 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 takes place. The equivalence point - the moment when the titrant is exactly enough to completely complete the reaction - is fixed using an indicator. Further, knowing the concentration and volume of the added titrant solution, the acidity of the solution is calculated.
- Effect of Temperature on pH Values
0.001 mol/L HCl at 20 °C has pH=3, at 30 °C pH=3
0.001 mol/L NaOH at 20 °C has pH=11.73, at 30 °C pH=10.83
In this article, we answer the questions of what is the acidity of wine and how it is determined. What is pH and why should the consumer know it. What is a degree of alcohol.
degree of alcohol
One of these abbreviations is very simple - ABV means the English "alcohol by volume", those. the alcohol content (in our case, ethanol) in the liquid volume. Usually measured as a percentage. And in colloquial speech it is called a degree. For example, the expression forty-degree vodka means that the proposed solution contains 40% - forty percent alcohol by volume.
Volume percentage or degree is measured in milliliters of "pure" ethanol in a volume of 100 ml at a temperature of 20 degrees Celsius.
In a nutshell, it is clear that if the bottle indicates ABV 5.5%, as, for example, on some Moscato d’Asti wines, then this lightly carbonated and low-alcohol wine can be lightly sipped all evening without fear of getting a hangover the next day. As they say, there is more alcohol in kefir!
By the way, this is why Moscato d'Asti and another Italian sparkling wine, Prosecco, are so popular at Hollywood parties. Everyone walks all evening with a glass in hand, but there are no drunks. And you can drive home yourself. Although judging by the news, the participants of these parties do not really care about the latter consideration.
A bit of theory - what is pH
On an intuitive level, we all roughly understand what acidity is. The degree of "acidity", so to speak. In chemistry, this term is acidity, lat. aciditas, eng. acidity - denotes a characteristic of the activity of hydrogen ions in solutions and liquids.
There are true (active) and total (titratable) acidity. In aqueous solutions, inorganic substances, i.e. salts, acids and alkalis (dissolved) are separated into their constituent ions.
At the same time, positively charged hydrogen ions H+ are carriers of acidic properties, and negatively charged ions OH-(they are also called hydroxyls) - carriers of alkaline properties.
A hundred years ago, chemists introduced a special hydrogen index, which is usually denoted by the symbols pH.
A bit of math
Non-nudists(c) and non-mathematicians(c) may skip this paragraph. And for the rest, we will inform you that for aqueous solutions, the equilibrium equation applies - the product of the activity of H + and OH- ions is constant. Under so-called normal conditions, ie. at a water temperature of 22°C and normal pressure, it is equal to 10 to the minus 14th power.
In 1909, the Danish biochemist Serensen introduced the pH value, which, by definition, is equal to the decimal logarithm of the activity of hydrogen ions, taken with a minus:
pH= - lg (H+ activity)
In a neutral medium, as we have just said, the activities of the ions are equal, i.e. the product of H+ activity and OH- activity is equal to the square of H+ activity. And it is equal to 10 to the minus 14th power.
So, after dividing 14 by 2, the negative decimal logarithm will be equal to 7. This means that (at a temperature of 22 ° C) the acidity of pure water, that is, neutral acidity, is equal to seven units: pH= 7.
Solutions and liquids are considered acidic if they pH less than 7, and alkaline, if more.
Typically, food products, including wine, tend to be acidic. Alkaline reactions are chemical dough leavening agents (soda, ammonium carbonate) and products prepared with their use, such as cookies and gingerbread.
Three types of acidity
Let's get back to guilt. The term "acidity" is one of the most used in the analysis, description and production of wines. In fact, acidity is one of the most important characteristics of wine chemistry and taste. There are three types of acidity in winemaking:
- total or titrated
- active or true - this is the [hydrogen] indicator of activity pH
- volatile acidity
Titratable acidity
Titratable or total acidity determines the content in the juice or wine of all free acids and their acid salts in the aggregate.
Its value is determined by the amount of alkali (for example, caustic soda or potassium) needed to neutralize these acids. That is, the amount of alkali that must be added to wine in order to obtain an absolutely neutral solution from it (pH=7.0).
Total acidity is measured in grams per litre.
Active acidity
Active or true acidity pH . Mathematically, this is the negative logarithm of the concentration of hydrogen ions, as mentioned above. Technically, this is the most accurate measure of wine acidity.
It depends on the amount of the strongest acids contained in the wine. Strong acids are those that have the highest dissociation constant (Kd) [acids].
An example of typical acids ordered by "strength", that is, in descending order of the dissociation constant (degree of acid):
- Lemon Cd = 8.4 10-4
- Amber Cd = 7.4 10-4
- Apple Cd = 3.95 10-4
- Dairy Kd = 1.4 10-4
From the value pH depends on the quantitative ratio of primary and secondary fermentation products, the wine's tendency to oxidation, crystalline and biological turbidity, susceptibility to defects and disease resistance of wine.
Examples
A simple explanation of the logarithmic relationship. Solution with pH= 3 is ten times more acidic than a solution with pH= 4. Or, for a more practical example, wine with pH= 3.2 25% more acidic than wine with pH= 3.3.
If it is necessary to correct the acidity of the wine, winemakers add a mixture of 1.9 g/l of lactic acid and 2.27 g/l of tartaric (dioxisuccinic or tartaric) acid. This makes it possible to reduce pH approximately by 0.1 (range 3 to 4).
And if, for example, the wine turned out with pH = 3.7 and the winemaker wants to bring it to pH = 3.5, he will double this “dose”.
ValuepHfor some products
The table below shows the acidity values of some common foods and pure water at different temperatures:
| Product | Acidity, pH |
| Lemon juice | 2,1 |
| Wine, approx. | 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 |
Volatile acidity
Volatile acidity, or VA for short, is that portion of the acids in wine that can be detected by the nose.
Unlike those acids that are palpable to the taste (as we talked about above).
Volatile acidity, or in other words, souring of wine, is one of the most common defects. Its main culprits are acetic acid (smells like vinegar) and its ester, ethyl acetate (smells like nail polish).
The bacteria responsible for volatile acidity thrive under conditions of low acidity and high sugar content. In small concentrations, volatile acidity gives the wine a piquancy. And when the threshold is exceeded, the vinegar-lacquer component clogs useful aromas and spoils the taste of wine.
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