Calculations molar mass

The greater the mass of an individual atom, the greater the molar mass of the substance. However, most elements exist in nature as a mixture of isotopes. We saw in Section B, for instance, that neon exists as three isotopes, each with a different mass. In chemistry, we almost always deal with natural samples of elements, which have the natural abundance of isotopes. So, we need the average molar mass, the molar mass calculated by taking into account the masses of the isotopes and their relative abundances in typical samples ... 

Using the molar mass, calculate the moles of all weighed samples. The moles of substances are converted to molarities by dividing by the volume (in liters) of the solution. Molarities may also be determined from pipet or buret readings using the dilution equation. (If a buret is used, one of the volumes is calculated from the difference between the initial and final readings.) The dilution equation may be needed to calculate the concentration of each reactant immediately after all the solutions are mixed. 

FIGURE 16.9 Schematic representation of principle of the molar mass calculation from the SEC chromatogram. The linear or polynomial calibration dependence log M vs. or log M [t ] vs. Er is obtained with help of the narrow molar mass distribution calibration materials (Section 16.8.3). The heights indicate concentration of each fraction i within sample (c =hJYh. The advanced computer software considers rather the areas of segments than their heights. The molar mass for each or segment i is taken from the calibration dependence. 

Molar mass distributions of PDADMAC were also determined by fractionation using dioxane/methanol system [144] and from sedimentation velocity measurements in 1 m NaCl solution [134]. The molar mass calculations were based on the s-M relation [134] ... 

The approximate molar mass, calculated from the gas density data, is 89 g/mol. The empirical formula, calculated from the percentage composition data, is C2H3O with the empirical formula unit mass of 43.0. The exact molar mass must be (2)(43) = 86.0 g/mol since this is the only multiple of 43.0 (whole-number multiple) reasonably close to the approximate molecular formula of 89 g/mol. The molecule must be the equivalent of 2 empirical formulas CqHgO. 

Determine the molar mass of calcium oxalate. Use the mass of calcium oxalate and its molar mass to find the amount (in mol) of calcium oxalate. Write the net ionic equation for the formation of calcium oxalate. From the coefficients in the net ionic equation, find the amount of oxalate ions (in mol). Calculate the mass of oxalate ions from the amount of oxalate ions (in mol) and the molar mass. Calculate the mass percent of oxalate ions in rhubarb leaves from the mass of the leaves and the mass of the oxalate ions present. 

How do your results compare with the theoretical molar mass calculated from the periodic table ... 

The calculation of copolymer molar mass averages and so on, and copolymer polydispersity D is done as in conventional GPC calculations using the copolymer molar mass calculated from Eq. (3). 

SHE (standard hydrogen electrode), 622 sickle cell anemia, 721, 721/ side reactions, 316 significant figures, 56-59, 56/ 57/ in molar mass calculations, 233, 233/ in scientific notation, 62-63... 

In the formula for a hydrate, the number of water molecules associated with each formula unit of the compound is written following a dot for example, Na2CO3T0H2O. This compound is called sodium carbonate decahydrate. In the word decahydrate, the prefix deca- means ten and the root word hydrate refers to water. Decahydrate means that ten molecules of water are associated with one formula unit of compound. The mass of water associated with a formula unit must be included in molar mass calculations. Hydrates are found with a variety of numbers of water molecules. Table 11-1 lists some common hydrates. 

For most practical purposes we are interested in the masses of reactants and products, because those are the quantities that are directly measured. In this case, the molar masses (calculated from a table of atomic masses) are used to convert the number of moles of a substance (in moles) to its mass (in grams), as illustrated by Example 2.6. Sometimes, however, we are also interested in knowing the number of molecules in a sample. The mole allows us to convert easily from mass to numbers of molecules as follows ... 

The molar mass calculation follows from the ideal gas law ... 

In a separate experiment, the molar mass was determined to be 86.2 g/mol. Gomparing this with the molar mass calculated for the empirical formula. 

Molar mass calculated from formula I o Measured molar mass 1... 

Calculated molar mast Measured pressure 1 -t- a Measured molar mass Calculated pressure 1... 

Equation (6-52) generally will be used here. An apparent molar mass A/app can be defined as a molar mass calculated from experimental data at finite concentrations from an equation applicable to infinite dilution only ... 

Thus, the light scattering function P(d) and also, via Equation (9-81), the mean square radius of gyration are z averages. The molar masses calculable from the radii of gyration with the aid of a calibration function represent, according to the shape of the particle, different averages i.e., (Mz) for coils in the theta state, ((Mz+i) (Mz)f for rods, etc. 

The SEC curves of these polyethers show low molar masses, calculated by using polystyrene standards. 

Often, size exclusion chromatograms (SEC) (compare section 11.7, Size Exclusion Chromatography) of polymers under study are expressed as differential representations of molar mass dispersity. The chromatographic retention volumes are directly transformed into the molar masses. This approach renders useful immediate information about tendencies of molar mass evolution in the course of building or decomposition polyreactions but the absolute values of molar mass can be only rarely extracted from it. As a rale, polystyrene calibrations are applied for molar mass calculation so that one deals with the polystyrene equivalent molar masses, not with the absolute values. The resulting dispersity (distribution) functions may be heavily skewed because the linear part of the calibration dependence for the polymer under study may exhibit well different slope compared with the polystyrene calibration, which was employed for the transformation of retention volumes into molar masses. 

Most periodic tables provide molar masses with four or five significant figures for the elements. How accurately would you have to measure the mass of a sample of roughly 100 g to make a calculation of the number of moles of the chemical to have its significant figures limited by the molar mass calculation rather than the mass measurement ... 

Strategy This problem can be divided into two parts. First, it asks for the empirical formula of the compound from the percent by mass of Si and F. Second, the information provided enables us to calculate the molar mass of the compound and hence determine its molecular formula. What is the relationship between empirical molar mass and molar mass calculated from the molecular formula ... 

Comparison of Molar Mass Calculated from Separation under... 

Comparison of Molar Masses Calculated from Separation under Critical Conditions and other Methods... 

Note The term molecular weight is deprecated because weight is the gravitational force on an object that varies with geographical location. Historically, the term has been used to denote the molar mass calculated using isotope averaged atomic masses for the constituent elements. 

Assuming that the two original polymer samples and the polymer produced by the ester interchange reaction have the ideal distributions of molar mass calculate Mn and for the mixture before and after the ester interchange reaction. 

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