Atomic and Molecular Weights

The molecular weight (mean relative molecular mass) was obtained by determination of density but, in order to determine that the gas was monatomic and its atomic and molecular weights identical, it was necessary to measure the velocity of sound in the gas and to derive from this the ratio of its specific heats kinetic theory predicts that Cp/C = 1.67 for a monatomic and 1.40 for a diatomic gas. 

The theory was advanced further when it was postulated that the reaction mechanism can be controlled not only by heat, but also by the diffusion of certain active species such as radicals. As described in the preceding section, low-atomic- and molecular-weight particles can readily diffuse back and initiate further reactions. 

The bovine spleen enzyme is dimeric, has a molecular weight of nearly 40 000 and contains two iron centres.822 One of these can be removed reversibly by treatment of the protein with dithionite.823 Conflicting results have been reported for uteroferrin one group has found two iron atoms per 40 000 molecular weight,824 while another group reported one iron atom and molecular weight 35 000.825... 

Ex. 14 The specific heat of a gas at constant volume is 0.152 and that at constant pressure is 0.215. Calculate the atomicity and molecular weight of the gas. Also name the gas. 

Wider use of heteropolymolybdates, in both science and industry, has been hindered by the complexity and confusion of the voluminous literature that has accumulated since Berzelius first observed compounds of this type in 1826. Analyses reported in the older literature are often inaccurate since the atomic and molecular weights are so high that small analytical errors produce great errors in the formulas reported degradation was often overlooked, and much of the work was unwittingly performed on mixtures. Accordingly, the earlier literature (though often extremely valuable)... 

The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kg of carbon-12. Although it is defined in terms of the number of entities, in practice, 1 mol of atoms, molecules, or specific formula units of a substance is measured by weighing M x (1 mol) of the substance, where M is the molar mass, the mass per unit amount of substance. Molar mass is synonymous with the terms atomic weight, for atoms, and molecular weight, for molecules or formula units, respectively, and is reported in grams per mole (g mol ). 

Calculation of Atomic and Molecular Weights from Experimental Data. — Many of the experiments in this book furnish data for the calculation of approximate atomic and molecular weights. 

This result agrees closely with 18, the molecular weight of water. These results are only approximate, but they serve to illustrate some of the methods employed in the determination of atomic and molecular weights. 

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