Carbon gas. Basic chemical properties of carbon dioxide
Carbon dioxide, or carbon dioxide, or CO 2 is one of the most common gaseous substances on Earth. It surrounds us throughout our lives. Carbon dioxide is colorless, tasteless and odorless and cannot be felt by humans in any way.
It is an important participant in the metabolism of living organisms. The gas itself is not poisonous, but does not support breathing, so exceeding its concentration leads to a deterioration in the supply of oxygen to the body’s tissues and to suffocation. Carbon dioxide is widely used in everyday life and in industry.
What is carbon dioxide
At atmospheric pressure and room temperature Carbon dioxide is in a gaseous state. This is its most common form, in which it participates in the processes of respiration, photosynthesis and metabolism of living organisms.
When cooled to -78 °C, it, bypassing the liquid phase, crystallizes and forms the so-called “dry ice”, widely used as a safe refrigerant in food and chemical industry and in street vending and refrigerated transport.
At special conditions- pressure of tens of atmospheres - carbon dioxide turns into a liquid state of aggregation. This occurs on the seabed, at a depth of over 600 m.
Properties of carbon dioxide
In the 17th century, Jean-Baptiste Van Helmont from Flanders discovered carbon dioxide and determined its formula. A detailed study and description was made a century later by the Scot Joseph Black. He studied the properties of carbon dioxide and conducted a series of experiments in which he proved that it is released during the respiration of animals.
The substance molecule contains one carbon atom and two oxygen atoms. The chemical formula of carbon dioxide is written as CO 2
Under normal conditions it has no taste, color or smell. Only by inhaling a large amount of it does a person feel a sour taste. It is produced by carbonic acid, which is formed in small doses when carbon dioxide is dissolved in saliva. This feature is used for making carbonated drinks. Bubbles in champagne, prosecco, beer and lemonade are carbon dioxide formed as a result of natural fermentation processes or added artificially to the drink.
Carbon dioxide is denser than air, so in the absence of ventilation it accumulates below. It does not support oxidative processes such as respiration and combustion.
Therefore, carbon dioxide is used in fire extinguishers. This property of carbon dioxide is illustrated using a trick - a burning candle is lowered into an “empty” glass, where it goes out. In reality the glass is filled with CO 2 .
Carbon dioxide in nature natural sources
These sources include oxidative processes of varying intensity:
- Respiration of living organisms. From the school course in chemistry and botany, everyone remembers that during photosynthesis, plants absorb carbon dioxide and release oxygen. But not everyone remembers that this happens only during the day, with a sufficient level of lighting. IN dark time Days, on the contrary, plants absorb oxygen and release carbon dioxide. So trying to improve the air quality in a room by turning it into thickets of ficus and geraniums can play a cruel joke.
- Eruptions and other volcanic activity. CO 2 is emitted from the depths of the Earth's mantle along with volcanic gases. In the valleys near the sources of eruptions there is so much gas that, accumulating in the lowlands, it causes suffocation of animals and even people. There are several known cases in Africa when entire villages were suffocated.
- Combustion and rotting of organic matter. Combustion and rotting are the same oxidation reaction, but occurring with at different speeds. Carbon-rich decaying organic matter from plants and animals, forest fires and smoldering peatlands are all sources of carbon dioxide.
- The largest natural reservoir of CO 2 is the waters of the world's oceans, in which it is dissolved.
Over millions of years of evolution of carbon-based life on Earth, many billions of tons of carbon dioxide have accumulated in various sources. Its immediate release into the atmosphere will lead to the death of all life on the planet due to the impossibility of breathing. It’s good that the probability of such a one-time release tends to zero.
AND artificial sources of carbon dioxide
Carbon dioxide also enters the atmosphere as a result of human activity. The most active sources in our time are considered to be:
- Industrial emissions occurring during fuel combustion in power plants and technological installations
- Exhaust gases from internal combustion engines of vehicles: cars, trains, airplanes and ships.
- Agricultural waste - rotting manure in large livestock complexes
In addition to direct emissions, there is also an indirect human impact on the CO 2 content in the atmosphere. This is massive deforestation in the tropical and subtropical zones, primarily in the Amazon basin.
Despite the fact that the Earth's atmosphere contains less than a percent of carbon dioxide, it has an increasing effect on climate and natural phenomena. Carbon dioxide is involved in the creation of the so-called greenhouse effect by absorbing the planet's thermal radiation and trapping that heat in the atmosphere. This leads to a gradual but very threatening increase in the average annual temperature of the planet, melting of mountain glaciers and polar ice caps, rising sea levels, flooding of coastal regions and deterioration of the climate in countries far from the sea.
It is significant that against the backdrop of general warming on the planet, there is a significant redistribution of air masses and sea currents, and in some regions the average annual temperature does not increase, but decreases. This gives a trump card to critics of the global warming theory, who accuse its supporters of falsifying facts and manipulating public opinion in favor of certain political centers of influence and financial and economic interests.
Humanity is trying to take control of the carbon dioxide content in the air; the Kyoto and Paris protocols were signed, imposing certain obligations on national economies. In addition, many leading automakers have announced that they will phase out models with internal combustion engines by 2020-25 and switch to hybrids and electric vehicles. However, some of the world's leading economies, such as China and the United States, are in no hurry to fulfill old and take on new obligations, citing a threat to the standard of living in their countries.
Carbon dioxide and us: why CO 2 is dangerous
Carbon dioxide is one of the metabolic products in the human body. It plays a large role in controlling breathing and blood supply to organs. An increase in CO 2 content in the blood causes the blood vessels to dilate, thus being able to transport more oxygen to tissues and organs. Likewise, the respiratory system is forced to become more active if the concentration of carbon dioxide in the body increases. This property is used in devices artificial ventilation lungs to spur the patient's own respiratory organs to greater activity.
In addition to the benefits mentioned, exceeding the concentration of CO 2 can also cause harm to the body. Increased levels in the inhaled air lead to nausea, headache, suffocation and even loss of consciousness. The body protests against carbon dioxide and sends signals to the person. With a further increase in concentration, oxygen starvation, or hypoxia, develops. Co 2 prevents oxygen from joining hemoglobin molecules, which carry out the movement of bound gases along circulatory system. Oxygen starvation leads to decreased performance, weakened reactions and abilities to analyze the situation and make decisions, apathy and can lead to death.
Such concentrations of carbon dioxide, unfortunately, are achievable not only in cramped mines, but also in poorly ventilated school classrooms, concert halls, office premises And vehicles- wherever a large number of people accumulate in a confined space without sufficient air exchange with the environment.
Main Application
CO 2 is widely used in industry and in everyday life - in fire extinguishers and for the production of soda, for cooling products and for creating an inert environment during welding.
The use of carbon dioxide is noted in such industries as:
- for cleaning surfaces with dry ice.
Pharmaceuticals
- for chemical synthesis of drug components;
- creating an inert atmosphere;
- normalization of the pH index of production waste.
Food industry
- production of carbonated drinks;
- packaging food in an inert atmosphere to extend shelf life;
- decaffeination of coffee beans;
- freezing or refrigerating food.
Medicine, tests and ecology
- Creation of a protective atmosphere during abdominal operations.
- Inclusion in respiratory mixtures as a respiratory stimulant.
- In chromatographic analyses.
- Maintaining the pH level in liquid industrial waste.
Electronics
- Cooling of electronic components and devices during temperature resistance testing.
- Abrasive cleaning in microelectronics (in the solid phase).
- Cleaning agent in the production of silicon crystals.
Chemical industry
Widely used in chemical synthesis as a reagent and as a temperature regulator in a reactor. CO 2 is excellent for disinfecting liquid waste with a low pH index.
It is also used for drying polymeric substances, plant or animal fiber materials, in pulp production to normalize the pH level of both the components of the main process and its waste.
Metallurgical industry
In metallurgy, CO 2 mainly serves the cause of ecology, protecting nature from harmful emissions by neutralizing them:
- In ferrous metallurgy - for neutralizing melting gases and for bottom mixing of the melt.
- In non-ferrous metallurgy in the production of lead, copper, nickel and zinc - to neutralize gases when transporting a ladle with a melt or hot ingots.
- As a reducing agent when organizing the circulation of acidic mine waters.
Carbon dioxide welding
A type of submerged arc welding is welding in a carbon dioxide environment. Operations welding work with carbon dioxide is carried out by a consumable electrode and distributed in the process installation work, eliminating defects and correcting parts with thin walls.
Before considering the chemical properties of carbon dioxide, let's find out some characteristics of this compound.
General information
Is essential component sparkling water. It is this that gives the drinks freshness and sparkling quality. This compound is an acidic, salt-forming oxide. carbon dioxide is 44 g/mol. This gas is heavier than air, so it accumulates in the lower part of the room. This compound is poorly soluble in water.
Chemical properties
Let us briefly consider the chemical properties of carbon dioxide. When interacting with water, weak carbonic acid is formed. Almost immediately after formation, it dissociates into hydrogen cations and carbonate or bicarbonate anions. The resulting compound interacts with active metals, oxides, and also with alkalis.
What are the basic chemical properties of carbon dioxide? The reaction equations confirm the acidic nature of this compound. (4) capable of forming carbonates with basic oxides.
Physical properties
Under normal conditions, this compound is in a gaseous state. When the pressure increases, it can be converted to a liquid state. This gas is colorless, odorless, and has a slight sour taste. Liquefied carbon dioxide is a colorless, transparent, highly mobile acid, similar in its external parameters to ether or alcohol.
The relative molecular weight of carbon dioxide is 44 g/mol. This is almost 1.5 times more than air.
If the temperature drops to -78.5 degrees Celsius, formation occurs. It is similar in hardness to chalk. When this substance evaporates, carbon monoxide gas is formed (4).
Qualitative reaction
When considering the chemical properties of carbon dioxide, it is necessary to highlight its qualitative reaction. When this chemical interacts with lime water, a cloudy precipitate of calcium carbonate is formed.
Cavendish managed to discover such characteristic physical properties carbon monoxide (4), both solubility in water and also high specific gravity.
Lavoisier conducted a study in which he tried to isolate pure metal from lead oxide.
The chemical properties of carbon dioxide revealed as a result of such studies became confirmation of the reducing properties of this compound. Lavoisier managed to obtain metal by calcining lead oxide with carbon monoxide (4). To make sure that the second substance was carbon monoxide (4), he passed lime water through the gas.
All the chemical properties of carbon dioxide confirm the acidic nature of this compound. In the earth's atmosphere this compound is found in sufficient quantity. With the systematic growth of this compound in the earth's atmosphere, serious climate change (global warming) is possible.
It is carbon dioxide that plays important role in living nature, because this chemical takes Active participation in the metabolism of living cells. It is this chemical compound that is the result of various oxidative processes associated with the respiration of living organisms.
Carbon dioxide contained in the earth's atmosphere is the main source of carbon for living plants. In the process of photosynthesis (in the light), the process of photosynthesis occurs, which is accompanied by the formation of glucose and the release of oxygen into the atmosphere.
Carbon dioxide is not toxic and does not support respiration. With an increased concentration of this substance in the atmosphere, a person experiences breath holding and severe headaches. In living organisms, carbon dioxide has important physiological significance; for example, it is necessary for the regulation of vascular tone.
Features of receiving
On an industrial scale, carbon dioxide can be separated from flue gas. In addition, CO2 is by-product decomposition of dolomite and limestone. Modern installations for the production of carbon dioxide involve the use of an aqueous solution of ethanamine, which adsorbs the gas contained in the flue gas.
In the laboratory, carbon dioxide is released by the reaction of carbonates or bicarbonates with acids.
Applications of carbon dioxide
This acidic oxide is used in industry as a leavening agent or preservative. On product packaging this compound is indicated as E290. In liquid form, carbon dioxide is used in fire extinguishers to extinguish fires. Carbon monoxide (4) is used to produce carbonated water and lemonade drinks.
Many aquarists know recommendations for using water that is softer and more acidic than aquarium water for breeding fish. It is convenient to use distilled water, soft and slightly acidic, for this purpose, mixing it with water from the aquarium. But it turns out that in this case the hardness of the source water decreases in proportion to the dilution, and pH practically does not change. Property to save the value of an indicator pH regardless of the degree of dilution, is called buffering. In this article we will get acquainted with the main components of aquarium water buffer systems: water acidity - pH, carbon dioxide content - CO 2, carbonate “hardness” - dKN(this value shows the content of bicarbonate ions in water NSO 3 -; in fishery hydrochemistry this parameter is called alkalinity), total hardness – dGН(for simplicity, it is assumed that it consists only of calcium ions - Ca++). Let us discuss their influence on the chemical composition of natural and aquarium water, the buffer properties themselves, as well as the mechanism of influence of the parameters under consideration on the fish body. Most of the chemical reactions discussed below are reversible, so it is important to first become familiar with the chemical properties of reversible reactions; It is convenient to do this using the example of water and pH.
- 6. CO 2 and physiology of respiration of aquarium fish
- 7. Mini-workshop
- 8. Literature used
1. ABOUT CHEMICAL EQUILIBRIA, UNITS OF MEASUREMENT AND pH
Although water is a weak electrolyte, it is capable of dissociation, described by the equation
H 2 O↔H + +OH -
This process is reversible, i.e.
H + +OH -↔H 2 O
From a chemical point of view, the hydrogen ion N + is always an acid. Ions capable of binding and neutralizing acid ( H+), are grounds. In our example, these are hydroxyl ions ( HE -), but in aquarium practice, as will be shown below, the dominant base is the hydrocrabonate ion NSO 3 -, carbonate “hardness” ion. Both reactions proceed at quite measurable rates, determined by concentration: the rates of chemical reactions are proportional to the product of the concentrations of the reacting substances. So for the reverse reaction of water dissociation H + +OH - >H 2 O its speed will be expressed as follows:
V arr = K arr [H + ]
TO– proportionality coefficient, called reaction rate constant.
-square brackets indicate molar concentration of a substance, i.e. number of moles of substance in 1 liter of solution. A mole can be defined as the weight in grams (or volume in liters - for gases) of 6 10 23 particles (molecules, ions) of a substance - Avogadro's number. The number showing the weight of 6 10 23 particles in grams is equal to the number showing the weight of one molecule in daltons.
So, for example, the expression denotes the molar concentration of an aqueous solution... water. The molecular weight of water is 18 daltons (two hydrogen atoms of 1d, plus an oxygen atom of 16d), corresponding to 1 mol (1M) H 2 O– 18 grams. Then 1 liter (1000 grams) of water contains 1000:18 = 55.56 moles of water, i.e. =55.56M=const.
Since dissociation is a reversible process ( H 2 O- H + +OH -), then provided that the rates of forward and reverse reactions are equal ( V pr =V arr), a state of chemical equilibrium occurs in which the reaction products and reactants are in constant and definite proportions: K pr = K arr. If we combine the constants on one side of the equation and the reactants on the other, we get
K pr / K arr = / = K
Where TO is also a constant and is called equilibrium constant.
The last equation is a mathematical expression of the so-called. law of mass action: in a state of chemical equilibrium, the ratio of the products of equilibrium concentrations of reagents is a constant value. The equilibrium constant shows at what proportions of reactants chemical equilibrium occurs. Knowing the meaning TO, you can predict the direction and depth of a chemical reaction. If K>1, the reaction proceeds in the forward direction if TO<1 - in the opposite. Using the equilibrium constant, chemical equations can be treated as algebraic and the corresponding calculations can be made. Their accuracy is not very high, but they are relatively simple and intuitive, which allows for a deeper understanding of the meaning of the processes under consideration. The numerical value of the equilibrium constant is individual and constant for each reversible chemical reaction. It is determined experimentally, and these values are given in chemical reference books.
In our example K = / = 1.8 10 -16. Because the =55.56 =const, then it can be combined with K on the left side of the equation. Then:
K==(1.8 10 -16) (55.56)=1 10 -14 = const. = K w
The water dissociation equation transformed into this form is called the ionic product of water and is designated K w. Meaning K w remains constant at any concentration values H+ And HE -, i.e. with increasing concentration of hydrogen ions H+, the concentration of hydroxyl ions decreases – OH - and vice versa. So, for example, if = 10 -6 , That = K w / = (10 -14)/(10 -6)=10 -8. But K w = (10 -6) . (10 -8) =10 -14 = const. From the ionic product of water it follows that in a state of equilibrium = = √K w =√1 10 -14 = 10 -7 M.
The unambiguous relationship between the concentration of hydrogen and hydroxyl ions in an aqueous solution allows one of these values to be used to characterize the acidity or alkalinity of the environment. It is customary to use the concentration of hydrogen ions H+. Since it is inconvenient to operate with values of the order of 10 -7, in 1909 the Swedish chemist K. Sörensen proposed using the negative logarithm of the concentration of hydrogen ions for this purpose H+ and marked it pH, from lat. potentia hydrogeni – the power of hydrogen: pH = -lg. Then the expression =10 - 7 can be written briefly as pH=7. Because the proposed parameter does not have units of measurement, it is called an indicator ( pH). The convenience of Serenzon's proposal seems obvious, but he was criticized by his contemporaries for the unusual inverse relationship between the concentration of hydrogen ions H+ and the value of the indicator pH: with increasing concentration H+, i.e. with increasing acidity of the solution, the value of the indicator pH decreases. From the ionic product of water it follows that the indicator pH can take values from 0 to 14 with a neutral point pH=7. The human taste organs begin to distinguish sour taste from the value of the indicator pH=3.5 and below.
For aquarium hobby the range is relevant pH 4.5-9.5(only it will be considered below) and the following scale with a variable division value is traditionally accepted:
- pH<6 -sour
- pH 6.0-6.5– slightly acidic
- pH 6.5-6.8– very slightly acidic
- pH 6.8-7.2–neutral
pH 7.2-7.5– very slightly alkaline
pH 7.5-8.0- slightly alkaline
pH>8– alkaline
In practice, in most cases, a coarser scale with a constant division value turns out to be much more informative:
- pH=5±0.5– sour
- pH=6±0.5– slightly acidic
- pH=7±0.5– neutral
- pH=8±0.5– slightly alkaline
- pH>8.5– alkaline
Wednesdays with pH<4,5 And pH>9.5 are biologically aggressive and should be considered unsuitable for aquarium inhabitants. Since the indicator pH is a logarithmic quantity, then the change pH by 1 unit means a change in the concentration of hydrogen ions by 10 times, by 2 - by 100 times, etc. A change in the concentration of H + by half leads to a change in the pH value by only 0.3 units.
Many aquarium fish can tolerate 100-fold (i.e. 2 units) without much harm to health. pH) changes in water acidity. Breeders of characins and other so-called soft-water fish, transfer spawners from a community aquarium (often with slightly alkaline water) to a spawning tank (with slightly acidic water) and back without intermediate adaptation. Practice also shows that most inhabitants of biotopes with acidic water in captivity feel better in water with pH 7.0-8.0. S. Spott believes pH 7.1-7.8 optimal for a freshwater aquarium.
Distilled water has pH 5.5–6.0, not expected pH=7. To understand this paradox, you need to get acquainted with the “noble family”: CO 2 and its derivatives.
2. CO2 WITH COMrades, pH, AND AGAIN UNITS OF MEASUREMENT
According to Henry's law, the gas content of the air mixture in water is proportional to its share in the air (partial pressure) and the absorption coefficient. Air contains up to 0.04% CO 2, which corresponds to its concentration up to 0.4 ml/l. Absorption coefficient CO 2 water=12.7. Then 1 liter of water can dissolve0.6 – 0.7 ml CO 2(ml, not mg!). For comparison, its biological antipode - oxygen, with a 20% content in the atmosphere and an absorption coefficient of 0.05, has a solubility of 7 ml/l. A comparison of absorption coefficients shows that, other things being equal, the solubility CO 2 significantly exceeds the solubility of oxygen. Let's try to figure out why there is such injustice.
Unlike oxygen and nitrogen, carbon dioxide is CO 2, is not a simple substance, but chemical compound– oxide. Like other oxides, it reacts with water to form oxide hydrates and, like other nonmetals, its hydroxide is acid (carbonic):
CO 2 + H 2 O = H 2 CO 3.
As a result, carbon dioxide owes its greater relative solubility to its chemical binding with water, which does not happen with either oxygen or nitrogen. Let us take a closer look at the acidic properties of carbonic acid, applying the law of mass action and taking into account that = const:
CO 2 +H 2 O=H + +HCO 3 -; K 1 = [H + ]/ = 4 10 -7
HCO 3 - =H + +CO 3 --; K 2 = / = 5.6 10 -11
Here K 1 And K 2– dissociation constants of carbonic acid in the 1st and 2nd stages.
Ions NSO 3 - are called bicarbonates (in the old literature bicarbonates), and the ions CO 3 --- carbonates. Order of magnitude K 1 And TO 2 suggests that carbonic acid is a very weak acid ( K 1<1 And K 2<1 ), and comparison of values K 1 And K 2– that its solution is dominated by bicarbonate ions ( K 1 >K 2).
From Eq. K 1 you can calculate the concentration of hydrogen ions H+:
= K 1 /
If we express concentration H+ through pH, as Henderson and Hasselbalch did in their time for the theory of buffer solutions, we get:
рН = рК 1 – log/
or more convenient
pH = pK 1 + log/
where, by analogy with pH, pK 1 = -lgK 1 = -lg4 10 -7 = 6.4 = const. Then pH=6.4 + lg/. The last equation is known as the Henderson–Hasselbalch equation. At least two important conclusions follow from the Henderson–Hasselbalch equation. Firstly, to analyze the value of the indicator pH it is necessary and sufficient to know the concentrations of the components only CO 2-systems. Secondly, the value of the indicator pH determined by the concentration ratio / , and not vice versa.
Because the content unknown, to calculate the concentration H+ in distilled water, you can use the formula accepted in analytical chemistry = √K 1 . Then pH = -log√K 1. To estimate the value of the indicator that interests us pH, let's return to units of measurement. From Henry's law it is known that the concentration CO 2 in distilled water is 0.6 ml/l. Expression means the molar concentration (see above) of carbon dioxide. 1M CO 2 weighs 44 grams, and under normal conditions takes up a volume of 22.4 liters. Then to solve the problem it is necessary to determine what fraction of 1M, i.e. from 22.4 liters are 0.6 ml. If the concentration CO 2 expressed not in volume, but in weight units, i.e. in mg/l, then the required fraction must be calculated from the molar weight CO 2– from 44 grams. Then the required value will be:
= x 10 -3 /22.4 = y 10 -3 /44
where x is volume (ml/l), y is weight (mg/l) concentration CO 2. The simplest calculations give an approximate value of 3 10 -5 M CO 2 , or 0.03mM. Then
pH = -lg√K 1 = -lg√(4 10 -7)(3 10 -5) = -lg√12 10 -12 = -lg(3.5 10 -6) = 5.5
which is quite consistent with the measured values.
From the Henderson-Hasselbalch equation it can be seen how the value of the indicator pH depends on attitude [HCO 3 - ]/[CO 2 ]. Approximately, we can assume that if the concentration of one component exceeds the concentration of another by 100 times, then the latter can be neglected. Then at [НСО 3 - ]/[СО 2 ] = 1/100 рН = 4.5, which can be considered the lower limit for CO 2-systems. Lower values of the indicator pH are caused by the presence of other mineral acids, such as sulfuric and hydrochloric, rather than carbonic acid. At [NSO 3 - ]/[CO 2 ] = 1/10, pH = 5.5. At [NSO 3 - ]/[CO 2 ] = 1, or [NSO 3 - ] = [CO 2 ], pH = 6.5. At [NSO 3 - ]/[CO 2 ] = 10, pH = 7.5. At [NSO 3 - ]/[CO 2 ] =100, pH = 8.5. It is believed that when pH>8.3(phenolphthalein equivalence point) there is practically no free carbon dioxide in water.
3. NATURAL WATER AND CARBON DIOXIDE EQUILIBRIUM
In nature, atmospheric moisture, saturated CO 2 air and falling with precipitation, it is filtered through the geological weathering crust. It is generally accepted that there it, interacting with the mineral part of the weathering crust, is enriched in the so-called. typomorphic ions: Ca++, Mg++, Na+, SO 4 --, Cl - and forms its chemical composition.
However, the works of V.I. Vernadsky and B.B. Polynov showed that the chemical composition of surface and groundwater In regions with a humid and moderately humid climate, the soil forms primarily. The influence of the weathering crust is associated with its geological age, i.e. with the degree of leaching. Decaying plant residues are added to water CO 2, NSO 3 - and ash elements in a proportion corresponding to their content in living plant matter: Ca>Na>Mg. It is curious that almost all over the world drinking water, also used in aquarium science, contains bicarbonate ion as the dominant anion NSO 3 -, and from cations – Ca++, Na+, Mg++, often with some share Fe. And the surface waters of the humid tropics are generally surprisingly uniform in chemical composition, differing only in the degree of dilution. The hardness of such waters extremely rarely reaches values ( 8 ° dGH), usually remaining at a level up to 4 ° dGН. Due to the fact that in such waters = , they have a slightly acidic reaction and the value of the indicator pH 6.0-6.5. The abundance of leaf litter and its active destruction during large quantities precipitation can lead to very high levels in such waters CO 2 and humic substances (fulvic acids) with an almost complete absence of ash elements. These are the so-called "black waters" of the Amazon, in which the value of the indicator pH can drop to 4.5 and be additionally held by the so-called. humate buffer.
In arid and vegetation-poor regions, the formation of the ionic composition of surface waters is significantly influenced by the geological age of the rocks that make up the weathering crust and their chemical composition. In them pH and the proportions of typomorphic ions will differ from those given above. As a result, waters with a noticeable content are formed SO 4 - And Cl -, and of the cations may predominate Na + with a noticeable share Mg++. The total salt content—mineralization—also increases. Depending on the content of hydrocarbonates, the pH value of such waters varies on average from pH 7±0.5 before pH 8±0.5, and the rigidity is always higher 10 ° dGH. In stable alkaline waters, at pH>9, the main cations will always be Mg++ And Na+ with a noticeable potassium content, because Ca++ precipitates in the form of limestone. In this regard, the waters of the Great African Rift Valley, which is characterized by the so-called soda salinization. Moreover, even the waters of such giants as Lakes Victoria, Malawi and Tanganyika are characterized by increased mineralization and such a high content of hydrocarbonates that the carbonate “hardness” in their waters exceeds the general hardness: dKH>dGH.
СО 2 + Н 2 О↔Н + +НСО 3 - ↔2Н + + СО 3 --
In those regions where the weathering crust is young and contains limestone ( CaCO 3), carbon dioxide equilibrium is expressed by the equation
CaCO 3 + CO 2 + H 2 O = Ca ++ + 2HCO 3 -
Applying the law of mass action to this equation (see above) and taking into account that =const And =const(solid phase), we get:
2 / = K CO2
Where K CO2– carbon dioxide equilibrium constant.
If the concentration active ingredients expressed in millimoles (mM,10 -3 M), then K CO2= 34.3. From Eq. K CO2 instability of hydrocarbonates is visible: in the absence CO 2 , i.e. at =0 , the equation doesn't make sense. In the absence of carbon dioxide, bicarbonates decompose to CO 2 and alkalize the water: NCO 3 - →OH - +CO 2. Contents free CO 2(very insignificant for “lifeless” water), which ensures the stability of a given concentration of hydrocarbonates at a constant pH, is called equilibrium carbon dioxide - R. It is related to both the carbon dioxide content in the air and dKN water: with growth dKN the number is also increasing [CO 2 ] p. Content CO 2 V natural waters as a rule, close to equilibrium and this is precisely their feature, and not the values dKH, dGН And pH most often distinguishes the state of natural waters from aquarium water. Having solved the equation TO CO2 relatively CO 2, you can determine the concentration of equilibrium carbon dioxide:
p = 2 /K CO2
Since the concepts of total hardness, carbonate “hardness” and acidity are iconic in freshwater aquarium keeping, it is interesting that the equations are:
K 1 = /
And
K CO2 = 2 /
combine them into one system. By dividing K CO2 on TO 1 , we obtain a generalized equation:
K CO2 /K 1 =/
Let us recall that And pH combines an inversely proportional relationship. Then the last equation shows that the parameters are: dGH, dKH And pH are directly proportional. This means that in a state close to gas equilibrium, an increase in the concentration of one component will lead to an increase in the concentration of the others. This property clearly visible when compared chemical composition natural waters different regions: Harder waters have higher values pH And dKN.
Optimal content for fish CO 2 is 1–5 mg/l. Concentrations greater than 15 mg/l are hazardous to the health of many species of aquarium fish (see below).
Thus, from the point of view of carbon dioxide balance, the content CO 2 in natural waters is always close to R.
4. ABOUT AQUARIUM WATER AND SOLUBILITY PRODUCT
Aquarium water does not have an equilibrium content CO 2 basically. Measuring carbon dioxide content using CO 2-test allows you to determine the total carbon dioxide content – generally, the value of which, as a rule, exceeds the concentration of equilibrium carbon dioxide - total > p. This excess is called nonequilibrium carbon dioxide - ner. Then
ner = total – p
Both forms of carbon dioxide - equilibrium and nonequilibrium - are not measured, but only calculated parameters. It is nonequilibrium carbon dioxide that ensures active photosynthesis aquatic plants and on the other hand, it can create problems during maintenance individual species fish In a well-balanced aquarium, natural daily fluctuations in carbon dioxide levels will not cause the concentration to drop below R and do not exceed the buffer capacity of the aquarium water. As will be shown in the next chapter, the amplitude of these oscillations should not exceed ±0.5 r. But with an increase in carbon dioxide content by more than 0.5 rub, dynamics of the declared components CO 2-systems – dGH, dKH And pH, will be very different from natural: overall hardness ( dGH) in such a situation increases against the background of falling values pH And dKN. It is this situation that can fundamentally distinguish aquarium water from natural water. There is an increase dGH as a result of dissolution of limestone soil. In such water, vital processes of gas exchange in the body of fish can be hampered, in particular, excretion CO 2, and the emerging response pathological processes often lead to errors in assessing the situation (see below). In marine reef aquariums, such water can dissolve freshly deposited CaCO 3 skeleton of stony corals, including at the site of injury, which can lead to detachment of the polyp’s body from the skeleton and the death of the animal if the aquarium is healthy in other respects.
With an abundance of aquatic plants in the light, a situation is possible when generally<р . In this case, the plants will eke out a miserable existence, and the water will be prone to sedimentation. CaCO 3, especially on mature leaves. Therefore, in aquariums for growing aquatic plants, it is recommended to maintain ner< 3 – 5 мг/л . The latter inequality is also typical for marine waters of coral reefs. In oceanology, this situation is described by the so-called. index of water saturation with calcium carbonate. In such an environment, photosynthesis of symbiont zooxanthellae in the bodies of coral polyps further enhances the above inequality, which ultimately leads to the deposition CaCO 3 and growth of the polyp skeleton. Unfortunately, this parameter has not yet found application in marine aquarium keeping. Due to the importance of limestone solubility CaCO 3, let’s take a closer look at the chemistry of this process.
As is known, the precipitation of crystals of any substance from a solution begins when it is so-called. saturated concentrations, when water is no longer able to contain this substance. The aqueous solution above the sediment (solid phase) will always be saturated with ions of the substance, regardless of its solubility, and will be in a state of chemical equilibrium with the solid phase. For limestone this will be expressed by the equation: CaCO 3 (tv.) = Ca ++ + CO 3 -- (solution). Applying the law of mass action, we get: (r-r) / (tv.) =K. Because the (tv.) =const(solid phase), then (рр) =К. Because the last equation characterizes the ability of a substance to dissolve, then such a product of saturated concentrations of ions of poorly soluble substances is called the solubility product - ETC(compare with the ionic product of water K w).
PR CaCO3 = = 5 10 -9. Like the ionic product of water, PR CaCO3 remains constant, regardless of changes in the concentrations of calcium and carbonate ions. Then, if there is limestone in the aquarium soil, carbonate ions will always be present in the water in an amount determined PR CaCO3 and overall hardness:
= PR CaCO3 /
In the presence of nonequilibrium carbon dioxide in water, the reaction occurs:
CO 3 -- +CO 2 +H 2 O=2HCO 3 -
which reduces the saturation concentration of carbonate ions [CO 3 -- ]. As a result, in accordance with the solubility product, compensatory amounts will enter the water CO 3 -- from CaCO 3, i.e. the limestone will begin to dissolve. Because the CO 2 +H 2 O=H + +HCO 3 -, the meaning of the above equation can be formulated more precisely: CO 3 -- +H + =НСО 3 -. The last equation says that the carbonates found in water in accordance with PR CaCO3, neutralize acid ( H+), formed upon dissolution CO 2, resulting in pH water remains unchanged. Thus, we gradually came to where we started the conversation:
5. CARBONATE BUFFER SYSTEM
Solutions are called buffer if they have two properties:
A: Indicator value pH solutions does not depend on their concentration or the degree of their dilution.
B: When adding acid ( H+), or alkali ( HE -), the value of their indicator pH changes little until the concentration of one of the components of the buffer solution changes by more than half.
Solutions consisting of a weak acid and its salt have these properties. In aquarium practice, this acid is carbon dioxide, and its dominant salt is calcium bicarbonate - Ca(HCO 3) 2. On the other hand, increasing the content CO 2 above equilibrium is equivalent to adding acid to water - H+, and lowering its concentration below equilibrium is equivalent to adding alkali - HE -(decomposition of hydrocarbonates - see above). The amount of acid or alkali that must be added to the buffer solution (aquarium water) so that the value of the indicator pH changed by 1 unit is called buffer capacity. It follows that pH aquarium water begins to change before its buffer capacity is exhausted, but after exhaustion buffer capacity, pH changes already equivalent to the amount of added acid or alkali. The operation of the buffer system is based on the so-called. Le Chatelier's principle: chemical equilibrium always shifts in the direction opposite to the applied force. Let's look at the properties A And B buffer systems.
A. Independence pH buffer solutions on their concentration is derived from the Henderson-Hasselbalch equation: pH = pK 1 +lg/. Then at different concentrations NSO 3 - And CO 2 their attitude / may be unchanged. For example, / = 20/8 = 10/4 = 5/2 = 2,5/1 = 0,5/0,2 = 2,5 , - i.e. different waters with different carbonate “hardness” values dKN and content CO 2, but containing them in the same proportion, will have the same value of the indicator pH(see also chapter 2). Such waters will surely differ in their buffer capacity: the higher the concentration of the components of the buffer system, the greater its buffer capacity and vice versa.
Aquarists usually encounter this property of buffer systems during periods of spring and autumn floods, if water intake stations are supplied with surface rather than artesian water. During such periods, the buffer capacity of water may decrease so much that some fish species cannot withstand traditional dense stocking. Then stories begin to appear about mysterious diseases that have wiped out, for example, angelfish or swordtails and against which all medicines are powerless.
B. We can talk about three buffer systems of aquarium water, each of which is stable in its own range pH:
1 . pH<8,3 СО 2 /НСО 3 - bicarbonate buffer
2. pH=8.3 HCO 3 - bicarbonate buffer
3. pH>8.3 HCO 3 - /CO 3 -- carbonate buffer.
Let's consider our B in two versions: var. B1- with increasing content CO 2 and var. B2– with a decrease in its content.
B1. Concentration CO 2 increases (dense planting, very old water, overfeeding).
Acid properties CO 2 manifest themselves in the formation of hydrogen ions H+ when interacting with water: CO 2 +H 2 O→H + +HCO 3 -. Then the increase in concentration CO 2 is equivalent to an increase in the concentration of hydrogen ions H+. According to Le Chatelier's principle, this will lead to neutralization H+. In this case, buffer systems work as follows.
Carbonate buffer 3 : In the presence of carbonate soil, hydrogen ions will be absorbed by the carbonates present in the water: H + +CO 3 -- →НСО 3 -. The consequence of this reaction will be the dissolution CaCO 3 soil (see above).
Hydrocarbonate buffer 1 – 2 : by reaction H + +HCO 3 - →CO 2 +H 2 O. Stability pH will be achieved by reducing carbonate “hardness” dKN, and removal of the resulting CO 2- either through photosynthesis or through diffusion into the air (with proper aeration).
If the source of excess CO 2 will not be eliminated, then when the value decreases dKN twice the original pH water level will begin to decrease with a concomitant drop in the buffer capacity and an increase in overall hardness. When the value of the indicator pH decreases by 1 unit, the capacity of the buffer system will be exhausted. When value pH=6.5 content of remaining hydrocarbonates = , and when pH<6 bicarbonates will be present only in trace form.
As a result, stability pH will be paid by the price of the downgrade dKN, increase dGH and consumption of buffer water capacity. Such water will be very different from natural water (see above) and not every fish will be able to survive in it. In aquarium practice, it is generally accepted that the amount of bicarbonates corresponding to 4° is the lower limit of the norm. dKN. It can be added that for a number of species of aquarium fish (livebearers, angelfish, silversides, etc.), a decrease in carbonate “hardness” below 2° dKN may end tragically. But at the same time, many small characins, rasboras, and irises tolerate such water.
B2. Opposite processes - alkalization of water due to a decrease in the content CO 2 in the aquarium below equilibrium - possible either with active photosynthesis of plants, or with the artificial introduction of bicarbonates into the water in the form of baking soda - NaHCO 3. Then, according to Le Chatelier's principle, this will lead to the following resistance from the aquarium water buffer systems.
Hydrocarbonate buffer 1 : stability pH will be retained due to the dissociation of hydrocarbonates: НСО 3 - →Н + +СО 3 --. Then, following a decrease in content
CO 2, the amount of hydrocarbonates will decrease proportionally, and the value of the ratio [NSO 3 - ]/ remain constant (see property A, Henderson-Hasselbalch equation). When the carbon dioxide content drops below 0.5 rub, indicator value pH will begin to increase and may increase to pH=8.3. Upon reaching this value, hydrocarbonate buffer 1 exhausts its capabilities, since in such water CO 2 practically absent.
Bicarbonate buffer 2 holds value pH=8.3. This figure follows from the formula [H + ]=√K 1 K 2, Where K 1 And K 2– 1st and 2nd dissociation constants of carbonic acid (see above). Then:
pH = -lg√K 1 K 2 = -lg√(4 10 -7)(5.6 10 -11) = 8.3
Those. meaning pH solutions of any hydrocarbonates constantly, does not exceed pH=8.3 and is a consequence of the very chemical nature of these substances.
In the absence of CO 2 hydrocarbonates decompose according to the equation:
NCO 3 - →CO 2 +OH -, alkalizing the water and releasing CO 2 which plants consume. But the same bicarbonate neutralizes HE - according to the scheme: NCO 3 - →CO 3 -- +H +; And H + +OH - →H 2 O. Therefore, the pH value will remain stable, which is reflected by the overall equation:
2HCO 3 - →CO 3 -- +CO 2 +H 2 O
Stability pH again achieved by reducing the amount of bicarbonates, i.e. by reducing the buffer capacity of water. However, the aquarium test dKN this decrease is not felt due to the peculiarities of the analysis method itself.
Since the bicarbonate ion has the ability to dissociate both acidic and basic, i.e.: НСО 3 - →Н + +СО 3 -- And NCO 3 - →OH - +CO 2, then carbonate “hardness” dKN(bicarbonate content) is also a buffer system.
Artificial addition of bicarbonates to the water (usually in the form of baking soda) is sometimes practiced when keeping cichlids from the African Great Lakes and in marine aquariums. In this case, two strategies are implemented: increasing the buffer capacity of aquarium water and increasing the value of the indicator pH up to 8.3.
If quantity CO 2 in aquarium water will decrease further, then when its content drops by half compared to equilibrium, pH water will begin to increase. When the indicator exceeds pH values pH=8.3, carbon dioxide disappears from the water, and inorganic carbon is represented only by bicarbonates and carbonates.
Carbonate buffer 3 . When carbonates exceed the concentration corresponding to the solubility product =PR CaCO3 /, crystals will begin to form in the water CaCO 3. Since the main and only consumer CO 2 Since in a freshwater aquarium there are aquatic plants, the processes in question occur mainly on the surface of the green leaf. When increasing pH>8.3 The surface of mature leaves will begin to become covered with a lime crust, which is an excellent substrate for algae growth. Binding carbonates CO 3 --, formed CaCO 3 also maintains stability pH. However, in the absence of ions Ca++(in very soft water), with active photosynthesis, an increase in the concentration of carbonates will increase the value of the indicator pH due to hydrolysis of carbonates: CO 3 -- +H 2 O→OH - +HCO 3 -.
When the indicator value increases pH by 1 unit, compared to the initial one, the buffer capacity of water will be exhausted, and with a continuing drop in content CO 2, indicator value pH can quickly escalate to risky pH>8.5. As a result, the content drops CO 2 in aquarium water will lead to an increase in pH value with a slight decrease in overall hardness. In such water (also highly nonequilibrium, as in the variant B1) many soft-water fish will feel very uncomfortable.
Thus carbonate buffer system water combines traditional aquarium hydrochemical parameters: total and carbonate hardness, pH, as well as content CO 2. In a row dGH – pH - dKH – CO 2 the most conservative parameter is dGH, and the most changeable – CO 2. By degree of change dGH, pH and especially dKH compared to settled, aerated tap water one can judge the degree of intensity of the processes of respiration and photosynthesis in the aquarium. The depletion of the buffer capacity of aquarium water in either direction changes its ability to absorb CO 2, that it is precisely this property that often turns it into a highly nonequilibrium content CO 2 and radically distinguishes it from nature. Changing the ability of aquarium water to absorb fish exhalation CO 2, may exceed the physiological capabilities of the fish body to eliminate it. Since this affects the health of the fish population of the aquarium, you should become familiar with the peculiarities of the physiological action CO 2 on the fish body.
© Alexander Yanochkin, 2005
© Aqua Logo, 2005
Carbon dioxide is a colorless gas with a barely perceptible odor, non-toxic, heavier than air. Carbon dioxide is widely distributed in nature. It dissolves in water, forming carbonic acid H 2 CO 3, giving it a sour taste. The air contains about 0.03% carbon dioxide. The density is 1.524 times greater than the density of air and is equal to 0.001976 g/cm 3 (at zero temperature and pressure 101.3 kPa). Ionization potential 14.3V. Chemical formula - CO 2.
In welding production the term is used "carbon dioxide" cm. . In the "Rules for the device and safe operation pressure vessels" the term adopted "carbon dioxide", and in - term "carbon dioxide".
There are many ways to produce carbon dioxide, the main ones are discussed in the article.
The density of carbon dioxide depends on pressure, temperature and the state of aggregation in which it is found. At atmospheric pressure and a temperature of -78.5°C, carbon dioxide, bypassing the liquid state, turns into a white snow-like mass "dry ice".
Under a pressure of 528 kPa and at a temperature of -56.6 ° C, carbon dioxide can be in all three states (the so-called triple point).
Carbon dioxide is thermally stable, dissociating into carbon monoxide only at temperatures above 2000°C.
Carbon dioxide is first gas to be described as a discrete substance. In the seventeenth century, a Flemish chemist Jan Baptist van Helmont (Jan Baptist van Helmont) noticed that after burning coal in a closed vessel, the mass of ash was much less than the mass of the burned coal. He explained this by saying that coal was transformed into an invisible mass, which he called “gas.”
The properties of carbon dioxide were studied much later in 1750. Scottish physicist Joseph Black (Joseph Black).
He discovered that limestone (calcium carbonate CaCO 3), when heated or reacted with acids, releases a gas, which he called “bound air”. It turned out that “bound air” is denser than air and does not support combustion.
CaCO 3 + 2HCl = CO 2 + CaCl 2 + H 2 O
By passing “bound air” i.e. carbon dioxide CO 2 through an aqueous solution of lime Ca(OH) 2 calcium carbonate CaCO 3 is deposited to the bottom. Joseph Black used this experiment to prove that carbon dioxide is released through animal respiration.
CaO + H 2 O = Ca(OH) 2
Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O
Liquid carbon dioxide is a colorless, odorless liquid whose density varies greatly with temperature. It exists at room temperature only at pressures above 5.85 MPa. The density of liquid carbon dioxide is 0.771 g/cm 3 (20°C). At temperatures below +11°C it is heavier than water, and above +11°C it is lighter.
Specific gravity liquid dioxide carbon changes significantly with temperature, therefore, the amount of carbon dioxide is determined and sold by weight. The solubility of water in liquid carbon dioxide in the temperature range 5.8-22.9°C is not more than 0.05%.
Liquid carbon dioxide turns into gas when heat is supplied to it. Under normal conditions (20°C and 101.3 kPa) When 1 kg of liquid carbon dioxide evaporates, 509 liters of carbon dioxide are formed. When gas is withdrawn too quickly, the pressure in the cylinder decreases and the heat supply is insufficient, the carbon dioxide cools, the rate of its evaporation decreases and when it reaches the “triple point” it turns into dry ice, which clogs the hole in the reduction gear, and further gas extraction stops. When heated, dry ice directly turns into carbon dioxide, bypassing the liquid state. To evaporate dry ice, it is necessary to supply significantly more heat than to evaporate liquid carbon dioxide - therefore, if dry ice has formed in the cylinder, it evaporates slowly.
Liquid carbon dioxide was first produced in 1823. Humphry Davy(Humphry Davy) and Michael Faraday(Michael Faraday).
Solid carbon dioxide "dry ice", according to appearance resembles snow and ice. The carbon dioxide content obtained from dry ice briquettes is high - 99.93-99.99%. Moisture content is in the range of 0.06-0.13%. Dry ice while on outdoors, evaporates intensely, so containers are used for its storage and transportation. Carbon dioxide is produced from dry ice in special evaporators. Solid carbon dioxide (dry ice), supplied in accordance with GOST 12162.
Carbon dioxide is most often used:
- to create a protective environment for metals;
- in the production of carbonated drinks;
- refrigeration, freezing and storage food products;
- for fire extinguishing systems;
- for cleaning surfaces with dry ice.
The density of carbon dioxide is quite high, which allows the arc reaction space to be protected from contact with air gases and prevents nitriding at relatively low carbon dioxide consumption in the jet. Carbon dioxide is, during the welding process, it interacts with the weld metal and has an oxidizing and also carburizing effect on the metal of the weld pool.
Previously obstacles to the use of carbon dioxide as a protective medium were in the seams. The pores were caused by boiling of the solidifying metal of the weld pool from the release of carbon monoxide (CO) due to its insufficient deoxidation.
At high temperatures, carbon dioxide dissociates to form highly active free, monoatomic oxygen:
Oxidation of the weld metal released free from carbon dioxide during welding is neutralized by the content of an additional amount of alloying elements with a high affinity for oxygen, most often silicon and manganese (in excess of the amount required for alloying the weld metal) or fluxes introduced into the welding zone (welding).
Both carbon dioxide and carbon monoxide are practically insoluble in solid and molten metal. The free active oxidizes the elements present in the weld pool depending on their oxygen affinity and concentration according to the equation:
Me + O = MeO
where Me is a metal (manganese, aluminum, etc.).
In addition, carbon dioxide itself reacts with these elements.
As a result of these reactions, when welding in carbon dioxide, significant burnout of aluminum, titanium and zirconium is observed, and less intense burnout of silicon, manganese, chromium, vanadium, etc.
The oxidation of impurities occurs especially vigorously at . This is due to the fact that when welding with a consumable electrode, the interaction of the molten metal with the gas occurs when a drop remains at the end of the electrode and in the weld pool, and when welding with a non-consumable electrode, it occurs only in the pool. As is known, the interaction of gas with metal in the arc gap occurs much more intensely due to high temperature and a larger contact surface between metal and gas.
Due to the chemical activity of carbon dioxide in relation to tungsten, welding in this gas is carried out only with a consumable electrode.
Carbon dioxide is non-toxic and non-explosive. At concentrations of more than 5% (92 g/m3), carbon dioxide has a harmful effect on human health, since it is heavier than air and can accumulate in poorly ventilated areas near the floor. This reduces the volume fraction of oxygen in the air, which can cause oxygen deficiency and suffocation. Premises where welding is carried out using carbon dioxide must be equipped with a general exchange supply and exhaust ventilation. The maximum permissible concentration of carbon dioxide in the air of the working area is 9.2 g/m 3 (0.5%).
Carbon dioxide is supplied by . To obtain high-quality seams, gaseous and liquefied carbon dioxide of the highest and first grades is used.
Carbon dioxide is transported and stored in steel cylinders or large-capacity tanks in a liquid state, followed by gasification at the plant, with a centralized supply to welding stations through ramps. A standard one with a water capacity of 40 liters is filled with 25 kg of liquid carbon dioxide, which at normal pressure occupies 67.5% of the volume of the cylinder and produces 12.5 m 3 of carbon dioxide upon evaporation. Air accumulates in the upper part of the cylinder along with carbon dioxide gas. Water, which is heavier than liquid carbon dioxide, collects at the bottom of the cylinder.
To reduce the humidity of carbon dioxide, it is recommended to install the cylinder with the valve down and, after settling for 10...15 minutes, carefully open the valve and release moisture from the cylinder. Before welding it is necessary from normal installed cylinder release a small amount of gas to remove any trapped air. Some of the moisture is retained in carbon dioxide in the form of water vapor, worsening the welding of the seam.
When gas is released from the cylinder, due to the throttling effect and heat absorption during the evaporation of liquid carbon dioxide, the gas cools significantly. With intensive gas extraction, the reducer may become clogged with frozen moisture contained in carbon dioxide, as well as dry ice. To avoid this, when extracting carbon dioxide, a gas heater is installed in front of the reducer. The final removal of moisture after the gearbox is carried out with a special desiccant filled with glass wool and calcium chloride, silica helium, copper sulfate or other moisture absorbers
The carbon dioxide cylinder is painted black, with the words “CARBON ACID” written in yellow letters..
Colorless and odorless. The most important regulator of blood circulation and respiration.
Non-toxic. Without it, there would be no rich buns and pleasantly tart carbonated drinks.
From this article you will learn what carbon dioxide is and how it affects the human body.
Most of us don't remember well school course physicists and chemists, but they know: gases are invisible and, as a rule, intangible, and therefore insidious. Therefore, before answering the question of whether carbon dioxide is harmful to the body, let's remember what it is.
Earth Blanket
- carbon dioxide. It is also carbon dioxide, carbon monoxide (IV) or carbonic anhydride. Under normal conditions, it is a colorless, odorless gas with a sour taste.
Under atmospheric pressure, carbon dioxide has two states of aggregation: gaseous (carbon dioxide is heavier than air, poorly soluble in water) and solid (at -78 ºС it turns into dry ice).
Carbon dioxide is one of the main components environment. It is found in the air and underground mineral waters, is released during the respiration of humans and animals, and is involved in plant photosynthesis.
Carbon dioxide actively influences the climate. It regulates the heat exchange of the planet: it transmits ultraviolet radiation and blocks infrared radiation. In this regard, carbon dioxide is sometimes called the Earth's blanket.
O2 is energy. CO2 - spark
Carbon dioxide accompanies a person throughout his life. Being a natural regulator of respiration and blood circulation, carbon dioxide is an integral component of metabolism.
By inhaling, a person fills the lungs with oxygen.
At the same time, a two-way exchange occurs in the alveoli (special “bubbles” of the lungs): oxygen passes into the blood, and carbon dioxide is released from it.
The man exhales. CO2 is one of the end products of metabolism.
Figuratively speaking, oxygen is energy, and carbon dioxide is the spark that ignites it.
Inhaling about 30 liters of oxygen per hour, a person emits 20-25 liters of carbon dioxide.
Carbon dioxide is no less important for the body than oxygen. It is a physiological stimulant of respiration: it affects the cerebral cortex and stimulates the respiratory center. The signal for the next breath is not a lack of oxygen, but an excess of carbon dioxide. After all, metabolism in cells and tissues is continuous, and its end products must be constantly removed.
In addition, carbon dioxide affects the secretion of hormones, enzyme activity and the rate of biochemical processes.
Gas exchange equilibrium
Carbon dioxide is non-toxic, non-explosive and absolutely harmless to people. However, the balance of carbon dioxide and oxygen is extremely important for normal life. Lack and excess of carbon dioxide in the body leads to hypocapnia and hypercapnia, respectively.
Hypocapnia- lack of CO2 in the blood. It occurs as a result of deep, rapid breathing, when more oxygen enters the body than needed. For example, during too intense physical activity. The consequences can vary: from mild dizziness to loss of consciousness.
Hypercapnia- excess CO2 in the blood. A person (together with oxygen, nitrogen, water vapor and inert gases) contains 0.04% carbon dioxide, and exhales 4.4%. If you are in small room With poor ventilation, the concentration of carbon dioxide may exceed the norm. As a consequence, there may be headache, nausea, drowsiness. But most often hypercapnia accompanies extreme situations: a malfunction of the breathing apparatus, holding one’s breath under water, and others.
Thus, contrary to the opinion of most people, carbon dioxide in the quantities provided by nature is necessary for human life and health. In addition, it has found wide industrial application and brings many practical benefits to people.
Sparkling bubbles at the service of chefs
CO2 is used in many fields. But, perhaps, carbon dioxide is most in demand in the food industry and cooking.
Carbon dioxide is formed in yeast dough under the influence of fermentation. It is its bubbles that loosen the dough, making it airy and increasing its volume.
Various refreshing drinks are made using carbon dioxide: kvass, mineral water and other sodas beloved by children and adults.
These drinks are popular with millions of consumers around the world, largely due to the sparkling bubbles that burst so funny in the glass and “prick” the nose so pleasantly.
Can the carbon dioxide contained in carbonated drinks contribute to hypercapnia or cause any other harm to a healthy body? Of course not!
Firstly, the carbon dioxide used in the preparation of carbonated drinks is specially prepared for use in the food industry. In the quantities in which it is contained in soda, it is absolutely harmless to the body of healthy people.
Secondly, most of carbon dioxide evaporates immediately after opening the bottle. The remaining bubbles “evaporate” during the drinking process, leaving behind only a characteristic hiss. As a result, a negligible amount of carbon dioxide enters the body.
“Then why do doctors sometimes prohibit drinking carbonated drinks?” - you ask. According to the candidate of medical sciences, gastroenterologist Alena Aleksandrovna Tyazheva, this is due to the fact that there are a number of diseases of the gastrointestinal tract for which a special strict diet is prescribed. The list of contraindications includes not only drinks containing gas, but also many food products.
A healthy person can easily include a moderate amount of carbonated drinks in his diet and allow himself a glass of cola from time to time.
Conclusion
Carbon dioxide is necessary to support the life of both the planet and an individual organism. CO2 affects the climate, acting as a kind of blanket. Without it, metabolism is impossible: metabolic products leave the body with carbon dioxide. It is also an indispensable component of everyone’s favorite carbonated drinks. It is carbon dioxide that creates playful bubbles that tickle your nose. Moreover, for healthy person it is absolutely safe.