(IV), carbon dioxide or carbon dioxide. It is also called carbonic anhydride. It is a colorless, odorless gas with a slightly sour taste. Carbon dioxide is heavier than air and does not dissolve well in water. At temperatures below -78 degrees Celsius, it crystallizes and becomes like snow.

From a gaseous state, this substance passes into a solid state, since it cannot exist in a liquid state under atmospheric pressure conditions. Density carbon dioxide under normal conditions is 1.97 kg/m3 - 1.5 times higher Carbon dioxide in solid form is called "dry ice". AT liquid state where it can be stored long time, it changes as the pressure increases. Let's take a closer look at this substance and its chemical structure.

Carbon dioxide, whose formula is CO2, consists of carbon and oxygen, and it is obtained as a result of the combustion or decay of organic matter. Carbon monoxide is found in the air and underground mineral springs. Humans and animals also release carbon dioxide when they exhale air. Plants without lighting release it, and during photosynthesis intensively absorb it. Thanks to the process of cell metabolism of all living beings, carbon monoxide is one of the main components of the environment.

This gas is not toxic, but if it accumulates in high concentration, suffocation (hypercapnia) may begin, and with its deficiency, the opposite state develops - hypocapnia. Carbon dioxide transmits and reflects infrared. He is which directly affects global warming. This is due to the fact that the level of its content in the atmosphere is constantly growing, which leads to the greenhouse effect.

Carbon dioxide is produced industrially from smoke or furnace gases, or by decomposition of dolomite and limestone carbonates. The mixture of these gases is thoroughly washed with a special solution consisting of potassium carbonate. Further, it passes into bicarbonate and decomposes when heated, as a result of which carbon dioxide is released. Carbon dioxide (H2CO3) is formed from carbon dioxide dissolved in water, but in modern conditions get it and other, more progressive methods. After the carbon dioxide is cleaned, it is compressed, cooled and pumped into cylinders.

In industry, this substance is widely and universally used. Food workers use it as a leavening agent (for example, for making dough) or as a preservative (E290). With the help of carbon dioxide, various tonic drinks and sodas are produced, which are so loved not only by children, but also by adults. Carbon dioxide is used in the manufacture of baking soda, beer, sugar, sparkling wines.

Carbon dioxide is also used in the production of effective fire extinguishers. With the help of carbon dioxide, an active environment is created that is necessary for high temperature welding arc, carbon dioxide breaks down into oxygen and carbon monoxide. Oxygen interacts with liquid metal and oxidizes it. Carbon dioxide in canisters is used in air rifles and pistols.

Aeromodellers use this substance as fuel for their models. With the help of carbon dioxide, you can significantly increase the yield of crops grown in a greenhouse. It is also widely used in industry in which food is preserved much better. It is used as a refrigerant in refrigerators, freezers, electric generators and other thermal power plants.

Substance with chemical formula CO2 and molecular weight 44.011 g / mol, which can exist in four phase states - gaseous, liquid, solid and supercritical.

The gaseous state of CO2 is commonly known as carbon dioxide. At atmospheric pressure, it is a colorless gas without color and odor, at a temperature of +20? With a density of 1.839 kg / m? (1.52 times heavier than air), dissolves well in water (0.88 volume in 1 volume of water), partially interacting in it with the formation of carbonic acid. Included in the atmosphere on average 0.035% by volume. With a sharp cooling due to expansion (expanding), CO2 is able to desublimate - go immediately into a solid state, bypassing the liquid phase.

Gaseous carbon dioxide was previously often stored in stationary gas holders. Currently, this method of storage is not used; carbon dioxide in required quantity are obtained directly on site - by evaporating liquid carbon dioxide in a gasifier. Further, the gas can be easily pumped through any gas pipeline at a pressure of 2-6 atmospheres.

The liquid state of CO2 is technically called "liquid carbon dioxide" or simply "carbonic acid". It is a colorless, odorless liquid medium density 771 kg / m3, which exists only under a pressure of 3,482 ... 519 kPa at a temperature of 0 ... -56.5 degrees C ("low-temperature carbon dioxide"), or under a pressure of 3,482 ... 7,383 kPa at a temperature of 0 ... +31.0 deg.С ("carbon dioxide high pressure"). High-pressure carbon dioxide is most often obtained by compressing carbon dioxide to a condensation pressure, while cooling it with water. Low-temperature carbon dioxide, which is the main form of carbon dioxide for industrial consumption, is most often produced in a high-pressure cycle by three-stage cooling and throttling in special plants.

With a small and medium consumption of carbon dioxide (high pressure), tons, a variety of steel cylinders are used for its storage and transportation (from cans for household siphons to containers with a capacity of 55 liters). The most common is a 40 l cylinder with a working pressure of 15,000 kPa, containing 24 kg of carbon dioxide. Steel cylinders do not require additional care, carbon dioxide is stored without loss for a long time. High pressure carbon dioxide cylinders are painted black.

With significant consumption, for storage and transportation of low-temperature liquid carbon dioxide, isothermal tanks of the most diverse capacity, equipped with service refrigeration units, are used. There are accumulative (stationary) vertical and horizontal tanks with a capacity of 3 to 250 tons, transportable tanks with a capacity of 3 to 18 tons. Vertical tanks require the construction of a foundation and are used mainly in conditions of limited space for placement. The use of horizontal tanks makes it possible to reduce the cost of foundations, especially if there is a common frame with a carbon dioxide plant. The tanks consist of an internal welded vessel made of low-temperature steel and having polyurethane foam or vacuum thermal insulation; outer casing made of plastic, galvanized or stainless steel; pipelines, fittings and control devices. The inner and outer surfaces of the welded vessel are subjected to special treatment, due to which the probability of surface corrosion of the metal is reduced to a minimum. In expensive imported models, the outer sealed casing is made of aluminum. The use of tanks provides filling and discharge of liquid carbon dioxide; storage and transportation without loss of the product; visual control of weight and operating pressure during filling, storage and dispensing. All types of tanks are equipped with a multi-level security system. Safety valves allow inspection and repair without stopping and emptying the tank.

With an instantaneous decrease in pressure to atmospheric pressure, which occurs during injection into a special expansion chamber (throttling), liquid carbon dioxide instantly turns into a gas and a thin snow-like mass, which is pressed and carbon dioxide is obtained in a solid state, which is commonly called "dry ice". At atmospheric pressure, it is a white vitreous mass with a density of 1,562 kg / m?, with a temperature of -78.5 ° C, which sublimates in the open air - gradually evaporates, bypassing the liquid state. Dry ice can also be obtained directly from high-pressure plants used to produce low-temperature carbon dioxide from gas mixtures containing CO2 in an amount of at least 75-80%. The volumetric cooling capacity of dry ice is almost 3 times greater than that of water ice and is 573.6 kJ/kg.

Solid carbon dioxide is usually produced in briquettes 200 × 100 × 20-70 mm in size, in granules with a diameter of 3, 6, 10, 12 and 16 mm, rarely in the form of the finest powder (“dry snow”). Briquettes, pellets and snow are stored for no more than 1-2 days in stationary underground mine-type storages, divided into small compartments; transported in special insulated containers with safety valve. Containers are used different manufacturers with a capacity of 40 to 300 kg or more. Sublimation losses are, depending on the ambient temperature, 4-6% or more per day.

At a pressure of over 7.39 kPa and a temperature of more than 31.6 degrees C, carbon dioxide is in the so-called supercritical state, in which its density is like that of a liquid, and its viscosity and surface tension are like that of a gas. This unusual physical substance (fluid) is an excellent non-polar solvent. Supercritical CO2 is able to fully or selectively extract any non-polar constituents with a molecular weight of less than 2,000 daltons: terpene compounds, waxes, pigments, high molecular weight saturated and unsaturated fatty acids, alkaloids, fat-soluble vitamins and phytosterols. Insoluble substances for supercritical CO2 are cellulose, starch, high molecular weight organic and inorganic polymers, sugars, glycosidic substances, proteins, metals and many metal salts. Possessing similar properties, supercritical carbon dioxide is increasingly used in the processes of extraction, fractionation and impregnation of organic and inorganic substances. It is also a promising working fluid for modern heat engines.

• Specific gravity. The specific gravity of carbon dioxide depends on pressure, temperature and state of aggregation in which it is located.
• The critical temperature of carbon dioxide is +31 degrees. The specific gravity of carbon dioxide at 0 degrees and a pressure of 760 mm Hg. is equal to 1.9769 kg/m3.
• The molecular weight of carbon dioxide is 44.0. The relative weight of carbon dioxide compared to air is 1.529.
• Liquid carbon dioxide at temperatures above 0 deg. much lighter than water and can only be stored under pressure.
• The specific gravity of solid carbon dioxide depends on the method of its production. Liquid carbon dioxide, when frozen, turns into dry ice, which is a transparent, glassy solid. In this case, solid carbon dioxide has the highest density (at normal pressure in a vessel cooled to minus 79 degrees, the density is 1.56). Industrial solid carbon dioxide has White color, close to chalk in hardness,
• its specific gravity varies depending on the method of obtaining within 1.3 - 1.6.

• State equation. The relationship between the volume, temperature, and pressure of carbon dioxide is expressed by the equation
• V= R T/p - A, where
• V - volume, m3/kg;
• R - gas constant 848/44 = 19.273;
• T - temperature, K degrees;
• p pressure, kg/m2;
• A is an additional term characterizing the deviation from the equation of state for an ideal gas. It is expressed by the dependence A \u003d (0.0825 + (1.225) 10-7 p) / (T / 100) 10 / 3.

• Triple point of carbon dioxide. The triple point is characterized by a pressure of 5.28 ata (kg/cm2) and a temperature of minus 56.6 degrees.
• Carbon dioxide can exist in all three states (solid, liquid and gaseous) only at the triple point. At pressures below 5.28 ata (kg/cm2) (or at temperatures below minus 56.6 degrees), carbon dioxide can exist only in solid and gaseous states.
• In the vapor-liquid region, i.e. above the triple point, the following relations hold
• i "x + i" "y \u003d i,
• x + y = 1, where,
• x and y - the proportion of the substance in liquid and vapor form;
• i" is the enthalpy of the liquid;
• i"" - steam enthalpy;
• i is the enthalpy of the mixture.
• From these values ​​it is easy to determine the values ​​of x and y. Accordingly, for the region below the triple point, the following equations will be valid:
• i"" y + i"" z \u003d i,
• y + z = 1, where,
• i"" - enthalpy of solid carbon dioxide;
• z is the proportion of the substance in the solid state.
• At the triple point for three phases, there are also only two equations
• i"x + i""y + i"""z = i,
• x + y + z = 1.
• Knowing the values ​​of i," i"," i""" for the triple point and using the above equations, you can determine the enthalpy of the mixture for any point.

• Heat capacity. The heat capacity of carbon dioxide at a temperature of 20 degrees. and 1 ata is
• Ср = 0.202 and Сv = 0.156 kcal/kg*deg. Adiabatic exponent k = 1.30.
• The heat capacity of liquid carbon dioxide in the temperature range from -50 to +20 deg. characterized by the following values, kcal / kg * deg. :
• Deg.С -50 -40 -30 -20 -10 0 10 20
• Wed, 0.47 0.49 0.515 0.514 0.517 0.6 0.64 0.68

• Melting point. The melting of solid carbon dioxide occurs at temperatures and pressures corresponding to the triple point (t = -56.6 degrees and p = 5.28 atm) or above it.
• Below the triple point, solid carbon dioxide sublimates. The sublimation temperature is a function of pressure: at normal pressure it is -78.5 degrees, in vacuum it can be -100 degrees. and below.

• Enthalpy. The enthalpy of carbon dioxide vapor in a wide range of temperatures and pressures is determined by the Planck and Kupriyanov equation.
• i = 169.34 + (0.1955 + 0.000115t)t - 8.3724p(1 + 0.007424p)/0.01T(10/3), where
• I - kcal / kg, p - kg / cm2, T - deg. K, t - deg. C.
• The enthalpy of liquid carbon dioxide at any point can be easily determined by subtracting the latent heat of vaporization from the enthalpy of saturated steam. Similarly, by subtracting the latent heat of sublimation, one can determine the enthalpy of solid carbon dioxide.

• Thermal conductivity. Thermal conductivity of carbon dioxide at 0 deg. is 0.012 kcal / m * hour * deg. C, and at a temperature of -78 deg. it drops to 0.008 kcal/m*hour*deg.C.
• Data on the thermal conductivity of carbon dioxide in 10 4 tbsp. kcal/m*h*deg.С at above-zero temperatures are given in the table.
• Pressure, kg/cm2 10 deg. 20 deg. 30 deg. 40 deg.
• gaseous carbon dioxide
• 1 130 136 142 148
• 20 - 147 152 157
• 40 - 173 174 175
• 60 - - 228 213
• 80 - - - 325
• liquid carbonic acid
• 50 848 - - -
• 60 870 753 - -
• 70 888 776 - -
• 80 906 795 670
  The thermal conductivity of solid carbon dioxide can be calculated by the formula:
  236.5 / T1.216 st., kcal / m * hour * deg. C.

• Thermal expansion coefficient. The volumetric expansion coefficient a of solid carbon dioxide is calculated depending on the change specific gravity and temperature. The linear expansion coefficient is determined by the expression b = a/3. In the temperature range from -56 to -80 degrees. the coefficients have the following values: a * 10 * 5st. \u003d 185.5-117.0, b * 10 * 5 st. = 61.8-39.0.

• Viscosity. Viscosity of carbon dioxide 10 * 6st. depending on pressure and temperature (kg*sec/m2)
• Pressure, ata -15 degrees. 0 deg. 20 deg. 40 deg.
• 5 1,38 1,42 1,49 1,60
• 30 12,04 1,63 1,61 1,72
• 75 13,13 12,01 8,32 2,30

• Dielectric constant. The dielectric constant of liquid carbon dioxide at 50 - 125 ati is in the range of 1.6016 - 1.6425.
• Dielectric constant of carbon dioxide at 15 deg. and pressure 9.4 - 39 atm 1.009 - 1.060.

• Moisture content of carbon dioxide. The content of water vapor in moist carbon dioxide is determined using the equation,
• X = 18/44 * p'/p - p' = 0.41 p'/p - p' kg/kg, where
• p' - partial pressure of water vapor at 100% saturation;
• p is the total pressure of the vapor-gas mixture.

• Solubility of carbon dioxide in water. The solubility of gases is measured by volumes of gas reduced to normal conditions (0 degrees, C and 760 mm Hg) per volume of solvent.
• The solubility of carbon dioxide in water at moderate temperatures and pressures up to 4 - 5 atm obeys Henry's law, which is expressed by the equation
• P \u003d H X, where
• P is the partial pressure of the gas above the liquid;
• X is the amount of gas in moles;
• H is Henry's coefficient.

• Liquid carbon dioxide as a solvent. The solubility of lubricating oil in liquid carbon dioxide at a temperature of -20 deg. up to +25 deg. is 0.388 g in 100 CO2,
• and increases to 0.718 g in 100 g of CO2 at a temperature of +25 degrees. WITH.
• The solubility of water in liquid carbon dioxide in the temperature range from -5.8 to +22.9 degrees. is not more than 0.05% by weight.

Safety

According to the degree of impact on the human body, gaseous carbon dioxide belongs to the 4th hazard class according to GOST 12.1.007-76 " Harmful substances. Classification and General requirements security." Maximum allowable concentration in air working area not established, when assessing this concentration, one should be guided by the standards for coal and ozocerite mines, set within 0.5%.

When using dry ice, when using vessels with liquid low-temperature carbon dioxide, safety measures must be observed to prevent frostbite of the hands and other parts of the worker's body.

Loss of strength, weakness, headache, depression - is this condition familiar? Most often this happens in autumn and winter, and feeling unwell attributed to lack sunlight. But it's not about him, but about the excess carbon dioxide in the air you breathe. The situation with the level of CO₂ in residential premises and transport in our country is truly catastrophic. stuffiness, high humidity and mold are also the result of a lack of ventilation. Sealed plastic windows And the air conditioners only make matters worse. Do you know that with a twofold excess (relative to the street background) of the level of carbon dioxide in the air, brain activity decreases by 2 times? By the way, yawning students at lectures are an indicator of high CO₂ content in the classroom. And very often there is no ventilation and in office buildings. What productivity can we talk about if a person simply does not have brains?

So let's start with the basics. A person breathes in oxygen and releases carbon dioxide. Carbon dioxide is also released when hydrocarbons are burned. The average level of CO₂ on our planet in this moment is about 400 PPM (Parts per million - parts per million, or 0.04%) and is constantly growing due to constant growth consumption of petroleum products. At the same time, it is worth knowing that trees absorb carbon dioxide and this is precisely their main function (and not, as it is mistakenly believed that they only produce oxygen).

As long as a person is outdoors, there are no problems, but they begin when he is indoors. If a person is locked in a sealed room without fresh air, then he will die not from a lack of oxygen, as most people mistakenly believe, but from a multiple excess of carbon dioxide, which this person himself developed in his lungs. Let's set aside the problems of ventilation of public transport (I will write about this separately) and turn our attention to city apartments / country houses, in which there is a massive lack of ventilation.

At the same time, a person spends at least a third of his life in his house / apartment, but in reality half - you can’t save on your own health!

2. The problem of high CO₂ content in the air is especially relevant in the cold season, because In the summer, almost all windows are constantly open. And with the onset of cold weather, the windows are opened less and less, ultimately reducing to episodic ventilation. And, what a coincidence, it is in the cold season that depression, drowsiness and loss of strength appear.

3. Previously, there was even such a tradition - to seal the cracks on the windows before the cold weather. Often, together with window vents, they completely excluded the flow of fresh air into the house. I emphasize again that Fresh air is needed not because it contains the oxygen necessary for breathing, but in order to reduce the excess carbon dioxide content by replacing the air in the room.

4. Many people think that they also have a hood (in apartments, at least in the kitchen and in the bathroom), and the room will be ventilated through it. Yeah, in addition, installing plastic windows that are completely airtight. But how will the air go into the exhaust if you do not have an inflow in the form of either slots in the frames or an open window? And with good traction, it usually pulls air from the entrance.

5. It's worse just to put the air conditioner in the form of a split system and use it with the windows closed. Remember, when the air conditioner is running, DO NOT close the windows! Here is a modern hermetic country house, which has no gaps in the building envelope. And do not be led by stories that wood or aerated concrete "breathe" and therefore you can not give a damn about ventilation. Remember, this term refers to the high vapor permeability of the material, and not the ability to supply fresh outdoor air into the house.

6. Most are limited to a fan on the hood from the bathroom and kitchen. Okay, turn on the fan, all windows and doors are closed in the house. What will be the result? That's right, there will be a rarefaction in the house, because the new air has nowhere to come from. To natural ventilation work, fresh air must enter the house.

7. For measuring the level of carbon dioxide in the air, relatively affordable sensors with an NDIR sensor have now appeared. The non-dispersive infrared method (NDIR) is based on the change in the intensity of infrared radiation before and after absorption in an infrared detector with selective sensitivity. Initially, I was going to buy such a sensor on aliexpress last year (then it cost about $ 100), but the increased price due to the growth of the dollar made me think and look for alternative options. Unexpectedly, this sensor was found in Russia under Russian brand for the same $100 at last year's exchange rate. In total, I found the best offer on Yandex.Market and purchased the sensor at a price of 3,500 rubles. The model is called MT8057. Of course, the sensor has an error, but it is not important when it comes to the fact that we need measurements with an excess of carbon dioxide concentration several times higher than the norm.

8. Closed plastic windows, air conditioners - all this is nonsense compared to the gas stove in the apartment (for the photo I lit gas burner, because to shoot the plate, it had to be washed).

9. So, all attention is on the chart. Kitchen 9 square meters, ceilings 3 meters high, opened door to the kitchen (!), a closed window, there is a hood with a natural impulse (draft is weak in summer), one person. The sensor is placed at a height of 1 meter from the floor, on dining table. The "normal" level of CO₂ in a room without people is about 600 PPM. One person comes - the level of CO₂ instantly rises. Leaves - falls. Comes again - rises again. And after that it turns on one (!) gas burner. The level of CO₂ almost instantly rises above 2000 PPM. Anxiety! We open the porthole. We observe how the concentration of carbon dioxide in the air slowly decreases. And add 1-2 more people here. Even if you do not turn on the gas stove, then 3 adults without performing heavy physical work raise the level of CO₂ in the room to a critical level in 30 minutes.

Cook for gas stove? Be sure to open the window and turn on the hood (do both at the same time).

Did you turn on the air conditioner? Be sure to open the window.

Are you just in the room? Be sure to open the hatch. And if there are a lot of people in the room, open the window.

And at night, during sleep, the window must be kept open.

In short, you either need to have a supply air duct or a permanently open window.

10. As for trees and how they can be useful. Their most important function during growth is the absorption of carbon dioxide. Few people think about why firewood burns and where there is so much energy in them. So this energy in the form of carbon accumulates in the trunk of a tree as a result of the absorption of carbon dioxide. Trees produce oxygen as a byproduct of photosynthesis.

11. Opening a window in the warm season is not difficult and in general the problem is not so urgent in summer (except when using air conditioners with closed windows). Problems begin in winter, because no one keeps the window open all the time, this is a huge uncontrolled loss of heat and it will be corny cold. It is precisely at this moment that it is worth raising the alarm. Health is priceless.

The problem is very serious and has a global character. For example, until the fall of last year, I didn’t think at all about the importance of ventilation for health: what’s in the apartment, what’s in country house. If you look into the past, then it is regular autumn depressions, drowsiness and Bad mood during the cold season in a city apartment, they made me think in the direction of leaving the city and building, so to speak. in autumn-winter I had a headache and there was a general weakness of the body when I was in the city. But as soon as I went out into nature, the problem disappeared. I didn't write it off as a lack of sunlight, but that wasn't the point. In winter, I stopped keeping the window open (it’s cold) and I got a multiple excess of CO₂ in the apartment.

The simplest and affordable solution problems - constantly keep the window open, or ventilate, focusing on the indicators from the CO₂ sensor. A normal level of CO₂ in a room can be considered a concentration of up to 1000 PPM, if it is higher, it is urgent to ventilate. Humidity can be considered an indirect indicator of the high concentration of carbon dioxide in the air. If, without objective reasons and a decrease in temperature, the humidity in the room begins to rise, it means that the level of CO₂ is increasing.

The danger of high concentrations of carbon dioxide in the air is that human body reacts with a very long delay. By the time you felt that it was stuffy in the room and you needed to ventilate it, you had already been in a room with a high content of CO₂ in the air for at least half an hour.

In the next post, I will talk about the problems with ventilation in public transport (buses, trains, planes). I will also show you how to properly organize ventilation in a country house, which for some reason everyone forgets about.

To be continued.

Articles on the topic, for self-study.

DEFINITION

Carbon dioxide (carbon dioxide, carboxylic anhydride, carbon dioxide) - carbon monoxide (IV).

The formula is CO2. Molar mass - 44 g/mol.

Chemical properties of carbon dioxide

Carbon dioxide belongs to the class of oxides of acids, that is, when it interacts with water, it forms an acid called charcoal. The carboxylic acid is chemically unstable and during the formation it immediately decomposes into its components, that is, the reaction of the interaction of carbon dioxide with water is reversible:

CO2 + H2O ↔ CO2 × H2O (solution) ↔ H2CO3.

When heated, carbon dioxide decomposes into carbon monoxide and oxygen:

2CO2 = 2CO + O2.

Like all acid oxides, carbon dioxide is characterized by interaction reactions with basic oxides (formed only by active metals) and bases:

CaO + CO2 = CaCO3;

Al2O3 + 3CO2 = Al2 (CO3) 3;

CO2 + NaOH (diluted) = NaHCO3;

CO2 + 2NaOH (conc) = Na2CO3 + H2O.

Carbon dioxide does not support combustion; only active metals burn in it:

CO2 + 2Mg = C + 2MgO(t^(\circ));

CO2 + 2Ca = C + 2CaO(t^(\circ)).

Carbon dioxide reacts with simple substances, such as hydrogen and carbon:

CO2 + 4H2 = CH4 + 2H2O (t ^ (\circ), kat = Cu2O);

CO2 + C = 2CO(t^(\circ)).

When carbon dioxide interacts with active metal peroxides, carbonates are formed and oxygen is released:

2CO2 + 2Na2O2 = 2Na2CO3 + O2.

A qualitative reaction to carbon dioxide is a reaction of its interaction with lime water (milk), that is, with calcium hydroxide, in which white precipitate- calcium carbonate:

CO2 + Ca (OH) 2 = CaCO3 ↓ + H2O.

Physical properties of carbon dioxide

Carbon dioxide is a gaseous substance without color or odor. Heavier than air. Thermal resistance. When compressed and cooled, it easily passes into a liquid and solid state. Carbon dioxide in the solid state of aggregation is called "dry ice" and readily sublimes at room temperature. Carbon dioxide is poorly soluble in water and partially reacts with it. Density - 1.977 g / l.

Production and use of carbon dioxide

Allocate industrial and laboratory methods for the production of carbon dioxide. So, in industry it is obtained by burning limestone (1) and in the laboratory under the action of strong acids on carbonate salts (2):

CaCO3 = CaO + CO2 (t^(\circ)) (1);

CaCO3 + 2HCl = CaCl2 + CO2 + H2O (2).

Carbon dioxide is used in food products(carbonation of lemonade), chemical (temperature control in the production of synthetic fibers), metallurgical (protection environment, e.g. brown gas deposition) and other industries.

Problem Solving Examples

Task

What volume of carbon dioxide will be released under the action of 200 g of a 10% solution of nitric acid per 90 g of calcium carbonate containing 8% impurities insoluble in acid?

Decision

Solution Molar mass of nitric acid and calcium carbonate, calculated using the table chemical elements D.I. Mendeleev - 63 and 100 g / mol, respectively.

We write the equation for the dissolution of limestone in nitric acid:

CaCO3 + 2HNO3 → Ca (NO3) 2 + CO2 + H2O.

ω (CaCO3) cl = 100% - ωadmixture = 100% - 8% = 92% = 0.92.

Then the mass of pure calcium carbonate:

m (CaCO3) cl = mlimestone × ω (CaCO3) cl / 100%;

m (CaCO3) Cl = 90 × 92/100% = 82.8 g

Amount of calcium carbonate:

n (CaCO3) = m (CaCO3) cl / M (CaCO3);

n (CaCO3) \u003d 82.8 / 100 \u003d 0.83 mol.

The mass of nitric acid in solution will be equal to:

m (HNO3) = m (HNO3) solution × ω (HNO3) / 100%;

m (HNO3) = 200 × 10/100% = 20 g.

The amount of calcium nitric acid substance:

n (HNO3) = m (HNO3) / M (HNO3);

n (HNO3) = 20/63 = 0.32 mol.

By comparing the amount of substances involved in the reaction, we determine that nitric acid is in short supply, so we carry out further calculations for nitric acid. According to the reaction equation for n (HNO3): n (CO2) = 2: 1, so n (CO2) = 1/2 × n (HNO3) = 0.16 mol. Then the volume of carbon dioxide will be equal to:

V(CO2) = n(CO2) × Vm;

V(CO2) = 0.16 x 22.4 = 3.58 g

Answer

The volume of carbon dioxide - 3.58 g.

Task

Set the amount of carbon dioxide weighing 35 g

Decision

Solution The mass of a substance and its volume are related to each other by the amount of the substance. Let's write the formulas for calculating the amount of a substance by mass and volume:

Equates the expressions written on the right, and we will express the volume:

V = m × Vm / M.

Calculate the volume of carbon dioxide from the resulting formula. Molar mass of carbon dioxide, calculated using the D.I. Mendeleev - 44 g / mol.

V (CO2) \u003d 35 × 22.4 / 44 \u003d 17.82 liters.

Answer

The volume of carbon dioxide is 17.82 liters.

Goals:

• Expand your understanding of discovery history, properties and practical application of carbon dioxide.
• To acquaint students with laboratory methods for obtaining carbon dioxide.
• Continue the formation of experimental skills of students.

Techniques used:“true and false statements”, “zigzag-1”, clusters.

Laboratory equipment: laboratory stand, apparatus for obtaining gases, 50 ml beaker, pieces of marble, hydrochloric acid (1:2), lime water, Mohr's clamp.

I. Call stage

At the challenge stage, the “true and false statements” technique is used.

Statements

II. Understanding stage

1. Organization of activities in working groups, the participants of which receive texts on the five main topics of the “zigzag”:

1. History of the discovery of carbon dioxide
2. carbon dioxide in nature
3. Getting carbon dioxide
4. Properties of carbon dioxide
5. Practical use carbon dioxide

There is an initial acquaintance with the text, primary reading.

2. Work in expert groups.

Expert groups unite “specialists” on specific issues. Their task is to carefully read the text, highlight key phrases and new concepts, or use clusters and various schemes for a graphic representation of the content of the text (work is carried out individually).

3. Selection of material, its structuring and addition (group work)

4. Preparation for translation of the text in working groups

• 1st group experts draws up a reference summary “History of the discovery of carbon dioxide”
• 2nd group experts draw up a diagram of the distribution of carbon dioxide in nature
• 3rd group experts draws up a scheme for obtaining carbon dioxide and a drawing of an installation for its production
• 4th group experts make a classification of the properties of carbon dioxide
• 5th group experts draws up a scheme for the practical use of carbon dioxide

5. Preparing for the presentation (poster)

III. Reflection stage

Return to working groups

1. Broadcast in a group of topics 1–5 consecutively. Collecting the plant for carbon dioxide production. Obtaining carbon dioxide and the study of its properties.
2. Discussion of the results of the experiment.
3. Presentation of individual topics.
4. Return to "true and false statements". Checking your initial assumptions. Placement of new icons.

It might look like this:

Statements
1. Carbon dioxide is a wild gas.
2. The seas and oceans contain 60 times more carbon dioxide than the earth's atmosphere.
3. natural springs carbon dioxide are called mofet.
4. In the vicinity of Naples there is a "Dog Cave", in which dogs cannot be.
5. In laboratories, carbon dioxide is produced by the action of sulfuric acid on pieces of marble.
6. Carbon dioxide is a colorless and odorless gas, lighter than air, and highly soluble in water.
7. Solid carbon dioxide is called "dry ice".
8. Lime water is a solution of calcium hydroxide in water.

Texts on the five main topics of the “zigzag”

1. History of the discovery of carbon dioxide

Carbon dioxide was the first among all other gases opposed to air under the name "wild gas" by the alchemist of the 16th century. Vant Helmont.

The discovery of CO 2 marked the beginning of a new branch of chemistry - pneumatochemistry (gas chemistry).

The Scottish chemist Joseph Black (1728 - 1799) in 1754 established that the lime mineral marble (calcium carbonate) decomposes with the release of gas when heated and forms quicklime (calcium oxide):

CaCO 3 CaO + CO 2
calcium carbonate calcium oxide carbon dioxide

The escaping gas could be recombined with calcium oxide and again get calcium carbonate:

CaO + CO 2 CaCO 3
calcium oxide carbon dioxide calcium carbonate

This gas was identical to the "wild gas" discovered by Van Helmont, but Black gave it a new name - "bound air" - because this gas could be bound and re-formed into a solid substance, and it also had the ability to be attracted by lime water (calcium hydroxide) and cause it to blur:

carbon dioxide calcium hydroxide calcium carbonate water

A few years later, Cavendish discovered two more characteristic physical properties of carbon dioxide - its high density and significant solubility in water.

2. Carbon dioxide in nature

The content of carbon dioxide in the atmosphere is relatively low, only 0.04–0.03% (by volume). CO 2 concentrated in the atmosphere has a mass of 2200 billion tons.
60 times more carbon dioxide is found in dissolved form in the seas and oceans.
During each year, about 1/50 of the total CO 2 contained in it is removed from the atmosphere by the vegetative cover of the globe in the process of photosynthesis, which turns minerals into organic substances.
The bulk of carbon dioxide in nature is formed as a result of various processes of decomposition of organic substances. Carbon dioxide is released during the respiration of plants, animals, microorganisms. The amount of carbon dioxide emitted by various industries is constantly increasing. Carbon dioxide is contained in the composition of volcanic gases, it is also released from the earth in volcanic areas. For several centuries it has been operating as a permanent CO 2 generator in the "Dog Cave" near the city of Naples in Italy. It is famous for the fact that dogs cannot be in it, and a person can stay there in a normal state. The fact is that in this cave carbon dioxide is released from the ground, and since it is 1.5 times heavier than air, it is located below, approximately at the height of a dog (0.5 m). In such air, where carbon dioxide is 14%, dogs (and other animals, of course) cannot breathe, but a standing adult does not feel an excess of carbon dioxide in this cave. The same caves exist in Yellowstone National Park (USA).
Natural sources of carbon dioxide are called mofetes. Mofety are characteristic of the last, late stage of the attenuation of volcanoes, in which, in particular, the famous Elbrus volcano is located. Therefore, there are numerous exits of hot springs saturated with carbon dioxide breaking through the snow and ice.
Outside the globe, carbon monoxide (IV) has been found in the atmospheres of Mars and Venus, “terrestrial-type” planets.

3. Getting carbon dioxide

In industry, carbon dioxide is obtained mainly as a by-product of alcoholic fermentation limestone roasting, etc.
AT chemical laboratories either use ready-made cylinders with liquid carbon dioxide, or get CO 2 in Kipp apparatus or a device for producing gases by the action of hydrochloric acid on pieces of marble:

CaCO 3 + 2HCl CaCl 2 + CO 2 + H 2 O
calcium carbonate hydrochloric acid calcium chloride carbon dioxide water

It is impossible to use sulfuric acid instead of hydrochloric acid, because then instead of water-soluble calcium chloride, gypsum would be obtained - calcium sulfate (CaSO 4) - a salt that is slightly soluble in water. Being deposited on pieces of marble, gypsum makes access to them extremely difficult for acids and thereby greatly slows down the course of the reaction.
To get carbon dioxide:

1. Fasten the device for obtaining gases in the leg of the laboratory tripod
2. Remove the funnel stopper from the test tube
3. Place 2-3 pieces of marble the size of ? peas
4. Insert the funnel stopper into the tube again. open clamp
5. Pour into the funnel (carefully!) hydrochloric acid(1:2) so that the acid lightly covers the marble
6. Fill the beaker with carbon monoxide (IV) and close the clamp.

4. Properties of carbon dioxide

CO 2 is a colorless gas, odorless, 1.5 times heavier than air, hardly mixes with it (according to D.I. Mendeleev, it “sinks” in air), which can be proved by the following experiment: over a glass, in which a burning candle is fixed, overturn a glass filled with carbon dioxide. The candle goes out instantly.
Carbon monoxide (IV) has acidic properties and when this gas is dissolved in water, carbonic acid is formed. When CO 2 is passed through water tinted with litmus, a change in the color of the indicator from purple to red can be observed.
The good solubility of carbon dioxide in water makes it impossible to collect it by the “water displacement” method.
A qualitative reaction to the content of carbon dioxide in the air is the passage of gas through a dilute solution of calcium hydroxide (lime water). Carbon dioxide causes the formation of insoluble calcium carbonate in this solution, as a result of which the solution becomes cloudy:

CO 2 + Ca(OH) 2 CaCO 3 + H 2 O
carbon dioxide calcium hydroxide calcium carbonate water

When an excess amount of CO2 is added, the cloudy solution becomes clear again due to the conversion of the insoluble carbonate to soluble calcium hydrogen carbonate:

CaCO 3 + H 2 O + CO 2 Ca (HCO 3) 2
calcium carbonate water carbon dioxide calcium bicarbonate

5. Practical application of carbon dioxide

Pressed solid carbon dioxide is called "dry ice".
Solid CO 2 is more like compacted dense snow, resembling chalk in hardness. The temperature of “dry ice” is -78 o C. Dry ice, unlike water ice, is dense. He sinks into the water, cooling it sharply. Burning gasoline can be quickly extinguished by throwing a few pieces of dry ice into the flames.
The main use of dry ice is the storage and transportation of food products: fish, meat, ice cream, etc. The value of dry ice lies not only in its cooling effect, but also in the fact that products in carbon dioxide do not mold or rot.
Dry ice is used in laboratories to test parts, devices, mechanisms that will serve at low temperatures. Dry ice is used to test the frost resistance of rubber tires.
Carbon dioxide is used to carbonate fruit and mineral waters, and in medicine - for carbon dioxide baths.
Liquid carbon dioxide is used in carbon dioxide fire extinguishers, aircraft and ship fire extinguishing systems, and carbon dioxide fire engines. It is especially effective in cases where water is unsuitable, for example, when extinguishing ignited flammable liquids or in the presence of electrical wiring or unique equipment in the room that can be damaged by water.
In many cases, CO 2 is not used in finished form, but is obtained in the process of using, for example, baking powders containing a mixture of sodium bicarbonate with acid potassium tartrate. When such powders are mixed with the dough, the salts dissolve and a reaction occurs with the release of CO 2 . As a result, the dough rises, filling with bubbles of carbon dioxide, and the product baked from it turns out to be soft and tasty.

Literature

1. Change // International journal about the development of thinking through reading and writing. - 2000. - Nos. 1, 2.
2. Modern student in the field of information and communication: Teaching aid. - St. Petersburg: PETROC, 2000.
3. Zagashev I.O., Zair-Bek S.I. Critical thinking: development technology. - St. Petersburg: Publishing house "Alliance" Delta ", 2003.