Molar weight, determination density

A plot of the density of sodium hydroxide solutions of varying composition is also shown in fig. 1.1. Electrolyte solutions are considerably more dense than water when they are concentrated. The important point to remember about these systems is that their compositions cannot be varied over the whole range because the solute is normally a solid at room temperature. Thus, the range of the weight fraction scale is determined by the solubility of the solid solute. In order to convert from molality to molarity, the solution density must be determined. Density data for common solutions can be found in data compilations such as the Landolt-Bornstein tables. 

Determinations of the density of gases and vapours are of value for the chemist on account of the fact that from the value of the density the molar weight of the substance in the gaseous condition at the temperature of vaporization can be calculated. 

The error in the determinations should not exceed 5 per cent Experiment.—Determiiu the Vapour Density and Molar Weight Ae one. 

The problem has two parts. First we must calculate the density of atmospheric air. To do this, we need to determine the molar mass of diy air, which is the weighted average of the molar masses of its... 

The key to any reaction experiment is moles. The numbers of moles may be calculated from various measurements. A sample may be weighed on a balance to give the mass, and the moles calculated with the formula weight. Or the mass of a substance may be determined using a volume measurement combined with the density. The volume of a solution may be measured with a pipet, or calculated from the final and initial readings from a buret. This volume, along with the molarity, can be used to calculate the moles present. The volume, temperature, and pressure of a gas can be measured and used to calculate the moles of a gas. You must be extremely careful on the AP exam to distinguish between those values that you measure and those that you calculate. 

Because the heat of vaporization of a polymer is not readily obtained. Small determined values for various components of a polymer chain to calculate the solubility parameter. These values are called molar attraction constants and are additive and have been used for estimation of the solubility parameter for nonpolar polymers. In this approach 8 = D%G/M, where D is density, G are the Small molar attraction constants, and M is the molecular weight of the particular repeat unit. As expected, the more polar units have greater G values while the less polar units have smaller G values. 

Ealy, Jr., "Determining the Molecular Weight of a Gas," Chemical Demonstrations, A Source-book for Teachers, Vol. 1 (American Chemical Society, Washington, DC, 1988), pp. 19-20. The molar mass of butane is determined by the vapor density method. 

Determine the volume of dilute nitric acid (density 1.11 g/mL, 19.0% HNO3 by weight) that can be prepared by diluting with water 50 mL of concentrated acid (density 1.42 g/mL, 69.8% HNO3 by weight). Calculate the molar concentrations and molalities of the concentrated and dilute acids. 

The molar volume of a pure substance can be obtained from density measurements, i.e., p = (molecular weight)/(molar volume). The volume contributed to a solution by the addition of 1 mole of an ion is, however, more difficult to determine. In fact, it has to be measured indirectly. This is because, upon entry into a solvent, the... 

It is possible, however, to determine a relationship exists between the fluid pressure and its density, thus allowing indirect measurement and control of the density. For an ideal gas, the relationship is simply, PV/RT= 1, where Fis the molar volume (reciprocal of the molar density). From the molecular weight of the gas (M), the mass density, p, can be calculated as M/V. The simple equation breaks down at the high densities characteristic of supercritical fluids, but, the work of Pitzer et allows the ideal gas law to be extended... 

The density of a liquid is defined as the weight of the liquid per unit volume (usually one milliliter). It is one of the more easily determined properties, and it is necessary for the calculation of molar refraction. Before simple refractometers became available, the density was considered a particularly important datum for characterizing liquids, but its use has now been largely superseded by the refractive index. However, it still remains a useful physical property. 

The universality class of the randomly branched polymers can be determined by constructing a universal molar mass distribution plot, like the ones shown in Fig. 6.26. First, the number density distribution function n(p, N) is determined from the concentration and weight-average molar... 

The concentration unit used for analysis is molarity, that is, the number of moles of solute per liter of solution. It should be noted that the molarity involves a weight/volume ratio, and that the volume involved is that of the total solution. In order to determine the molarity of the system being considered here, one must know the density of the solution. In general, this property cannot be determined from the densities of the individual components but must be found in an independent experiment. The density of acetonitrile-water solutions as a function of the weight fraction of acetonitrile is shown in fig. 1.1. From these data one finds that the density of the solution made of 10 g acetonitrile and 90 g water is 0.979 g mL at 25°C. Thus, the volume of the same solution is 102.15 mL and the corresponding molarity, 0.2437/0.10215 = 2.386 M. The relationship between the molarity cb and mole fraction xb is... 

The molecular weight per polymeric repeat unit is determined exactly from the structure of the polymeric repeat unit. The specific volume and the density are therefore both known if the molar volume is known. 

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