The molecular weight expressed as the sum of the masses of atoms in a molecule of a substance.Usually it is expressed in amu (atomic mass units), sometimes also called Dalton and is denoted D. For 1 amutoday adopted 1/12 weight C12 carbon atoms in units of mass equal 1,66057.10-27 kg.

Thus, the atomic weight of hydrogen equal to 1 indicates that a hydrogen atom H1 in 12 times lighter than the carbon atom C12.Multiplying the molecular weight of a chemical compound on 1,66057.10-27 obtain the value of the mass of the molecule in kilograms.

In practice, however, are more convenient size of bunt = M / D, where M - mass of the molecule in the same unit mass, and D. The molecular weight of oxygen, expressed in carbon units is 16 x 2 = 32 (diatomic oxygen molecule).Likewise, in chemical calculations and are calculated molecular mass of other compounds.The molecular weight of hydrogen, which has a diatomic molecule and is equal to, respectively, 2 x 1 = 2.

molecular weight - a characteristic of the aver

previously used concept in chemistry mole.Today this concept is replaced by the mole - the amount of substance that contains the number of particles (molecules, atoms, ions), equal to the Avogadro constant (6.022 x 1023).Until today, traditionally also used the term "molar (molecular) weight."But, unlike weight, which depends on the geographical coordinates of the mass - is a constant parameter, so still it is correct to use this term.

molecular weight of the air and the other gases, can be found by using the law of Avogadro.This law states that under the same conditions in the same volume of gas is present the same number of molecules.Consequently, under certain temperature and pressure, moles of gas will occupy the same volume.Given that this law strictly valid for ideal gases mol gas containing 6.022 x 1023 molecules it takes at 0 ° C and 1 atmosphere pressure and a volume of 22.414 liters.

molecular weight of air or any other gas components is as follows.It determines the mass of a known volume of gas at a certain pressure and temperature.Then introduced an amendment to the non-ideality of the real gas by using Clapeyron equation PV = RT provides volume to the conditions of a pressure of 1 atmosphere and 0 ° C. Then, knowing the volume and weight under these conditions for an ideal gas, it is easy to calculate the weight and 22.414 liters of gaseous substances investigatedie its molecular weight.And thus determines the molecular weight of air.

This method gives a fairly accurate values of molecular weights, which are sometimes even used to determine the atomic weights of chemical compounds.For a rough estimate of the molecular weight of the gas it is generally considered ideal, and any further adjustment is not done.

The above method is often used for determining the molecular weight of volatile liquids.