Molar mass of carbon dioxide.

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

The gaseous state of CO2 is commonly called carbon dioxide. At atmospheric pressure it is a colorless, odorless gas, 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 volumes in 1 volume of water), partially interacting in it with the formation of carbonic acid. Included in the atmosphere is an average of 0.035% by volume. During sudden cooling due to expansion (expansion), CO2 is able to desublimate - go directly into the solid state, bypassing the liquid phase.

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

The liquid state of CO2 is technically called “liquid carbon dioxide” or simply “carbon dioxide”. This is a colorless, odorless liquid with an average density of 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 degrees C (“carbon dioxide high pressure"). High-pressure carbon dioxide is most often produced by compressing carbon dioxide to condensation pressure while simultaneously cooling with water. Low-temperature carbon dioxide, which is the main form of carbon dioxide for industrial consumption, is most often produced through a high-pressure cycle by three-stage cooling and throttling in special installations.

For low and medium consumption of carbon dioxide (high pressure), a variety of steel cylinders are used for its storage and transportation (from cylinders for household siphons to containers with a capacity of 55 liters). The most common is a 40 liter cylinder with an operating 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.

In case of significant consumption, for the storage and transportation of low-temperature liquid carbon dioxide, isothermal tanks of various capacities are used, equipped with service refrigeration units. There are storage (stationary) vertical and horizontal tanks with a capacity from 3 to 250 tons, transportable tanks with a capacity from 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 station. 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 of stainless steel; pipelines, fittings and control devices. Internal and outer surface welded vessels are subjected to special treatment, due to which the likelihood of surface corrosion of the metal is reduced. In expensive imported models, the outer sealed casing is made of aluminum. The use of tanks ensures filling and draining of liquid carbon dioxide; storage and transportation without product loss; visual control weight and operating pressure during refueling, during 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 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 glassy mass with a density of 1,562 kg/m?, with a temperature of -78.5? C, which is outdoors sublimates - 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 amounts to 573.6 kJ/kg.

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

At a pressure above 7.39 kPa and a temperature above 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 those of a gas. This unusual physical substance (fluid) is an excellent non-polar solvent. Supercritical CO2 is capable of completely or selectively extracting any non-polar constituents with a molecular weight of less than 2,000 daltons: terpenes, waxes, pigments, high molecular weight saturated and unsaturated fatty acids, alkaloids, fat-soluble vitamins and phytosterols. Insoluble substances for supercritical CO2 are cellulose, starch, organic and inorganic high molecular weight polymers, sugars, glycosidic substances, proteins, metals and salts of many metals. 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 the pressure, temperature and state of aggregation in which it is located.
• The critical temperature of carbon dioxide is +31 degrees. Specific gravity of carbon dioxide at 0 degrees and a pressure of 760 mm Hg. 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 degrees. 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, hardness is close to chalk,
• its specific gravity varies depending on the production method in the range of 1.3 - 1.6.

• Equation of state. The relationship between 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 = (0.0825 + (1.225)10-7 r)/(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 gas) only at the triple point. At pressures below 5.28 ata (kg/cm2) (or at temperatures below minus 56.6 degrees), carbon dioxide can only exist in solid and gaseous states.
• In the vapor-liquid region, i.e. above the triple point, the following relations are valid
• i"x + i"" y = 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"" - enthalpy of steam;
• 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 = i,
• y + z = 1, where,
• i"" - enthalpy of solid carbon dioxide;
• z is the fraction 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 given 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 index k =1.30.
• The heat capacity of liquid carbon dioxide in the temperature range from -50 to +20 degrees. characterized by the following values, kcal/kg*deg. :
• Deg.C -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. Melting of solid carbon dioxide occurs at temperatures and pressures corresponding to the triple point (t = -56.6 degrees and p = 5.28 ata) 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 a vacuum it can be -100 degrees. and below.

• Enthalpy. The enthalpy of carbon dioxide vapor over a wide range of temperatures and pressures is determined using the Planck and Kupriyanov equation.
• i = 169.34 + (0.1955 + 0.000115t)t - 8.3724 p(1 + 0.007424p)/0.01T(10/3), where
• I - kcal/kg, p - kg/cm2, T - degrees K, t - degrees 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 vapor. Similarly, by subtracting the latent heat of sublimation, the enthalpy of solid carbon dioxide can be determined.

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

• 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. coefficients have the following values: a *10*5st. = 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, at -15 degrees. 0 deg. 20 deg. 40 degrees
• 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 degrees. and pressure 9.4 - 39 ati 1.009 - 1.060.

• Moisture content of carbon dioxide. The content of water vapor in wet 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 steam-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 = N X, where
• P is the partial pressure of gas above the liquid;
• X is the amount of gas in moles;
• H - Henry's coefficient.

• Liquid carbon dioxide as a solvent. Solubility of lubricating oil in liquid carbon dioxide at a temperature of -20 degrees. up to +25 degrees. is 0.388 g in 100 CO2,
• and increases to 0.718 g per 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 no more than 0.05% by weight.

Safety precautions

In terms of the degree of impact on the human body, carbon dioxide gas belongs to the 4th hazard class according to GOST 12.1.007-76 " Harmful substances. Classification and General requirements security." Maximum permissible concentration in air working area has not been established, when assessing this concentration one should focus on the standards for coal and ozokerite mines, set within 0.5%.

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

Instructions

Example 1: Determine the relative molecular weight of CO2. One molecule of carbon dioxide is made up of one carbon atom and two oxygen atoms. Find the atomic mass values ​​for these elements in the periodic table and write them down, rounding to the nearest whole number: Ar(C) = 12; Ar(O) = 16.

Calculate the relative mass of the CO2 molecule by adding the masses of the atoms that make it up: Mr(CO2) = 12 + 2*16 = 44.

Example 2. Consider how to express the mass of one gas molecule in grams using the example of carbon dioxide. Take 1 mole of CO2. The molar mass of CO2 is numerically equal to the molecular mass: M(CO2) = 44 g/mol. One mole of any contains 6.02*10^23 molecules. This is the number of Avogadro's constant and the symbol is Na. Find the mass of one molecule of carbon dioxide: m(CO2) = M(CO2)/Na = 44/6.02*10^23 = 7.31*10^(-23) .

Example 3. You are given a gas with a density of 1.34 g/l. You need to find the mass of one gas molecule. According to Avogadro's law, under normal conditions, one mole of any gas occupies 22.4 liters. Having determined the mass of 22.4 liters, you will find the molar mass of the gas: Mg = 22.4 * 1.34 = 30 g/mol
Now, knowing the mass of one mole, calculate the mass of one molecule similarly to example 2: m = 30/6.02*10^23 = 5*10^(-23) grams.

Sources:

• molecular weight of gas

You can calculate the mass of any molecule by knowing its chemical formula. For example, let us calculate the relative molecular mass of an alcohol molecule.

You will need

• Mendeleev table

Instructions

Consider the chemical formula of the molecule. Determine which atoms of chemical elements are included in its composition.

The alcohol formula is C2H5OH. The alcohol molecule contains 2 atoms, 6 hydrogen atoms and 1 oxygen atom.

Add up the atomic masses of all the elements, multiplying them by the atoms of the substance in the formula.

Thus, M(alcohol) = 2*12 + 6*1 + 16 = 24 + 6 + 16 = 46 atomic mass. We found the molecular weight of the alcohol molecule.

If the mass of a molecule is in grams rather than in atomic mass units, it should be remembered that one atomic mass unit is the mass of 1/12 of a carbon atom. Numerically 1 a.u.u. = 1.66*10^-27 kg.

Then the mass of the alcohol molecule is 46*1.66*10^-27 kg = 7.636*10^-26 kg.

note

In Mendeleev's periodic table chemical elements arranged in order of increasing atomic mass. Experimental methods for determining molecular weight have been developed mainly for solutions of substances and for gases. There is also a mass spectrometry method. The concept of molecular weight is of great practical importance for polymers. Polymers are substances consisting of repeating groups of atoms, but the number of these groups is not the same, so for polymers there is a concept of average molecular weight. By average molecular weight can indicate the degree of polymerization of a substance.

Helpful advice

Molecular mass is an important quantity for physicists and chemists. Knowing the molecular mass of a substance, you can immediately determine the density of the gas, find out the molarity of the substance in solution, and determine the composition and formula of the substance.

Sources:

• Molecular mass
• how to calculate the mass of a molecule

Mass is one of the most important physical characteristics of a body in space, characterizing the degree of its gravitational influence on the fulcrum. When it comes to calculating mass body, the so-called “rest mass” is meant. It's easy to calculate.

You will need

• p is the density of the substance from which this body consists (kg/m³);
• V is the volume of a given body, characterizing the amount of space it occupies (m³).

Instructions

Practical approach:
For the masses of various bodies, they use one of the most ancient inventions of mankind - scales. The first scales were lever scales. On one there was a reference weight, on the other -. Weights are used as reference weight indicators. When the weight of the weight/weights coincides with a given body, the lever goes into a state of rest, without bending to either side.

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In order to determine mass atom, find the molar mass of a monatomic substance using the periodic table. Then divide this mass by Avogadro's number (6.022 10^(23)). This will be the mass of the atom, in the units in which the molar mass was measured. The mass of a gas atom is found through its volume, which is easy to measure.

You will need

• To determine the mass of an atom of a substance, take the periodic table, a tape measure or ruler, a pressure gauge, or a thermometer.

Instructions

Determination of atomic mass solid or To determine the mass of an atom of a substance, determine it (what it consists of). In the periodic table, find the cell that describes the corresponding element. Find the mass of one mole of this substance in grams per mole that is in this cell (this number corresponds to the mass of the atom in atomic mass units). Divide the molar mass of the substance by 6.022 10^(23) (Avogadro's number), the result will be the substance in grams. You can determine the mass of an atom in another way. To do this, multiply the atomic mass of the substance in atomic mass units taken from the periodic table by the number 1.66 10^(-24). Get the mass of one atom in grams.

Determining the mass of a gas atom If there is an unknown gas in the vessel, determine its mass in grams by weighing the empty vessel and the vessel with the gas, and find the difference in their masses. After this, measure the volume of the vessel using a ruler or tape measure, followed by calculations or other methods. Express the result in . Use a pressure gauge to measure the gas pressure inside the vessel, and measure its temperature with a thermometer. If the thermometer scale is graduated in Celsius, determine the temperature in Kelvin. To do this, add the number 273 to the temperature value on the thermometer scale.

To determine gas, multiply the mass of a given volume of gas by its temperature and the number 8.31. Divide the result by the product of the gas, its volume and Avogadro’s number 6.022 10^(23) (m0=m 8.31 T/(P V NA)). The result will be the mass of the gas molecule in grams. If it is known that the gas molecule is diatomic (the gas is not inert), divide the resulting number by 2. By multiplying the result by 1.66 10^(-24), you can obtain its atomic mass in atomic mass units and determine the chemical formula of the gas.

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The molecular mass of a substance means the total atomic mass of all chemical elements that are part of this substance. To calculate the molecular mass substances, no special effort is required.

You will need

• Mendeleev table.

Instructions

Now you need to take a closer look at any of the elements in this table. Under the name of any of the elements indicated in the table there is a numerical value. This is precisely the atomic mass of this element.

Now it is worth looking at several examples of molecular mass calculations, based on the fact that atomic masses are now known. For example, you can calculate the molecular weight of a substance such as water (H2O). A water molecule contains one oxygen atom (O) and two hydrogen atoms (H). Then, having found the atomic masses of hydrogen and oxygen using the periodic table, we can begin to calculate the molecular mass:2*1.0008 (after all, there are two hydrogens) + 15.999 = 18.0006 amu (atomic mass units).

Another . The next substance, molecular mass which can be calculated, let it be ordinary table salt (NaCl). As can be seen from the molecular formula, a molecule of table salt contains one Na atom and one Cl atom. In this case, it is calculated as follows: 22.99 + 35.453 = 58.443 a.m.u.

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note

I would like to note that the atomic masses of isotopes of various substances differ from the atomic masses in the periodic table. This is due to the fact that the number of neutrons in the nucleus of an atom and inside an isotope of the same substance is different, therefore the atomic masses are also noticeably different. Therefore, it is customary to denote isotopes of various elements by the letter of a given element, adding its mass number in the upper left corner. An example of an isotope is deuterium (“heavy hydrogen”), the atomic mass of which is not one, like an ordinary atom, but two.

One of the first concepts that a student encounters when studying a chemistry course is mole. This value reflects the amount of substance in which there is a certain number of particles of Avogadro’s constant. The concept of "mole" was introduced in order to avoid complex mathematical calculations with large numbers smallest particles.

Instructions

Determine the number of particles contained in 1 mole of the substance. This value is a constant and is called Avogadro's constant. It is equal to NА=6.02*1023 mol-1. If you want to spend more accurate calculations, then the value of this value must be taken according to the information of the Committee on Data for and Technology CODATA, which recalculates Avogadro’s constant and approves the most exact values. For example, in 2011 it was accepted that NА = 6.022 140 78(18)×1023 mol-1.

Calculate the value of moles, which is equal to the ratio of the number of particles of a given substance to the value of Avogadro's constant.

Determine the value of a mole of a substance through its M. It has the dimension g/mol and is equal to the relative molecular mass Mr, which is determined from the periodic table for each element contained in the substance. For example, the molar value of methane CH4 is equal to the sum of the relative atomic masses and four hydrogens: 12+ 4x1. As a result, you get that M(CH4) = 16 g/mol. Next, study the condition of the problem and find out for what mass m of the substance it is necessary to determine the number of moles. It will be equal to the ratio of mass to molar mass.

Remember that the molar mass of a substance is determined by the quantitative and qualitative characteristics of its composition, so substances may have the same values mole at different masses.

Study the conditions of the problem; if it is necessary to determine the number of moles for a gaseous substance, then you can calculate it through volumes. In this case, it is necessary to find out the volume V of a given gas under conditions. After this, divide this value by the molar volume of the gas Vm, which is a constant and under normal conditions is equal to 22.4 l/mol.

Chemistry is an exact science, so when mixing different substances you simply need to know their precise proportions. To do this you need to be able to find mass substances. This can be done different ways, depending on what quantities you know.

Instructions

If you know the meanings substances and its quantity, use it to determine the mass substances another formula by multiplying the quantity value substances to its molar mass(m(x) = n*M). If the quantity substances unknown, but given the number of molecules in it, then use Avogadro's number. Find the quantity substances, dividing the number of molecules substances(N) by Avogadro's number (NA=6.022x1023): n=N/NA, and substitute into the formula above.

To find the molar mass complex substances, add up the atomic masses of all those included in it. Take atomic masses from the table of D.I. Mendeleev in the designations of the corresponding elements (for convenience, round atomic masses to the first decimal place). Then proceed in the formula by substituting the molar mass value into it. Don't forget about indices: what is the element's index in chemical formula(i.e. how many atoms are in the substance), by that amount you need to multiply the atomic mass.

If you have to deal with a solution, and you know the mass fraction of the desired substances, to determine the mass of this substances multiply the share substances on mass of the entire solution and divide the result by 100% (m(x) = w*m/100%).

Write an equation substances, from it calculate the amount received or spent substances, and then the resulting amount substances Substitute into the formula given to you.

Apply the formula: output=mp*100%/m(x). Then, depending on the mass that needs to be calculated, find mр or m. If the product yield is not given, then it can be assumed to be 100% (in real processes this is extremely rare).

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Helpful advice

Designations of quantities in the given formulas:
m(x) - mass of substance (calculated),
mp is the mass obtained in the real process,
V is the volume of the substance,
p is the density of the substance,
P - pressure,
n - amount of substance,
M is the molar mass of the substance,
w is the mass fraction of the substance,
N is the number of molecules,
NA - Avogadro's number
T - temperature in Kelvin.

Write down these tasks briefly, indicating formulas using alphabetic and numerical notations.

Check the condition and data carefully; the problem may contain a reaction equation.

Sources:

• How to solve simple chemistry problems

Molecular mass substances is the mass of a molecule, expressed in atomic units and numerically equal to the molar mass. When calculating in chemistry, physics and technology, the calculation of the molar mass of various substances is often used.

You will need

• - Mendeleev table;
• - table of molecular weights;
• - table of cryoscopic constant values.

Instructions

Find the required element in the periodic table. Pay attention to the fractional numbers under its sign. For example, O has a numerical value in the cell equal to 15.9994. This is the atomic mass of the element. Atomic mass must be multiplied by the index of the element. The index shows how much of an element is contained in a substance.

If given complex, then multiply the atomic mass each element by its index (if there is one atom of a particular element and there is no index, then multiply by one) and add the resulting atomic masses. For example, water is calculated as follows - MH2O = 2 MH + MO ≈ 2·1+16 = 18 a. eat.

Calculate molar mass using suitable formulas and equate it to molecular. Change the units of measurement from g/mol to amu. If pressure, volume, absolute Kelvin temperature and mass are given, calculate the molar mass gas according to the Mendeleev-Cliperon equation M=(m∙R∙T)/(P∙V), in which M is the molecular () in amu, R is the universal gas constant.

Calculate molar mass according to the formula M=m/n, where m is the mass of any given substances, n - chemical quantity substances. Express the quantity substances through Avogadro's number n=N/NA or using volume n=V/VM. Substitute into the formula above.

Find the molecular mass gas, if only the value of its volume is given. To do this, take a sealed cylinder of known volume and pump it out. Weigh it on a scale. Pump gas into the cylinder and measure again mass. The difference in mass of the cylinder with gas pumped into it and empty cylinder is the mass of a given gas.

Using a pressure gauge, find the pressure inside the cylinder (in Pascals). Use a thermometer to measure the ambient air, it is equal to the temperature inside the cylinder. Convert Celsius to Kelvin. To do this, add 273 to the resulting value. Find the molar mass according to the Mendeleev-Clapeyron equation given above. Convert it to molecular, replacing the units of measurement with a.m.u.

DEFINITION

Carbon monoxide (IV) (carbon dioxide) under normal conditions it is a colorless gas, heavier than air, thermally stable, and when compressed and cooled it easily transforms into liquid and solid (“dry ice”) states.

The structure of the molecule is shown in Fig. 1. Density - 1.997 g/l. It is poorly soluble in water, partially reacting with it. Shows acidic properties. Reduced by active metals, hydrogen and carbon.

Rice. 1. The structure of the carbon dioxide molecule.

The gross formula of carbon dioxide is CO 2 . As is known, the molecular mass of a molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule (the values ​​of the relative atomic masses taken from periodic table DI. Mendeleev, round to whole numbers).

Mr(CO 2) = Ar(C) + 2×Ar(O);

Mr(CO 2) = 12 + 2×16 = 12 + 32 = 44.

DEFINITION

Molar mass (M) is the mass of 1 mole of a substance.

It is easy to show that the numerical values ​​of the molar mass M and the relative molecular mass M r are equal, however, the first quantity has the dimension [M] = g/mol, and the second is dimensionless:

M = N A × m (1 molecule) = N A × M r × 1 amu = (N A ×1 amu) × M r = × M r .

It means that molar mass of carbon dioxide is 44 g/mol.

The molar mass of a substance in the gaseous state can be determined using the concept of its molar volume. To do this, find the volume occupied under normal conditions by a certain mass of a given substance, and then calculate the mass of 22.4 liters of this substance under the same conditions.

To achieve this goal (calculation of molar mass), it is possible to use the equation of state of an ideal gas (Mendeleev-Clapeyron equation):

where p is the gas pressure (Pa), V is the gas volume (m 3), m is the mass of the substance (g), M is the molar mass of the substance (g/mol), T - absolute temperature(K), R - universal gas constant equal to 8.314 J/(mol×K).

Examples of problem solving

EXAMPLE 1

EXAMPLE 2