Density and molar mass

Estimate the molar volume, Vh of TrCB from its density and molar mass given in Appendix C (see also Eq. 3-18) ... 

The Lorentz-Lorenz equation [2] defines the molar refraction, RD, as a function of the refractive index, density, and molar mass ... 

Still other applications of the ideal gas law make it possible to calculate such properties as density and molar mass. Densities are calculated by weighing a known volume of a gas at a known temperature and pressure, as shown in Figure 9.10. Using the ideal gas law to find the volume at STP and then dividing the measured mass by the volume gives the density at STP. Worked Example 9.7 gives a sample calculation. 

Furthermore, we know that the molar concentration of pure water, calculated from its density and molar mass, is 55.4 M at 25°C ... 

In this section, you will learn more about two properties of a gas that are closely related to molar volume density and molar mass. You have already encountered these properties, but now you will use them to help you with your gas calculations. 

The molar mass of a gas refers to the mass (in g) of one mole of the gas. You can calculate molar mass by adding the masses of atoms in the periodic table. You can also calculate molar mass by dividing the mass of a sample by the number of moles that are present. Molar mass is always expressed in the units g/mol. Table 12.2 summarizes molar volume, density, and molar mass. 

Table 12.2 Molar Volume, Density, and Molar Mass...

In this section, you learned how density and molar mass are related to the ideal gas law. You also learned how to identify an unknown substance by calculating its molar mass, both theoretically and in the laboratory. Before you continue, take the time to complete the following Section Review questions. They will help you remember what you have learned. 

You can memorize the equation involving gas density and molar mass, but it is better simply to remember the ideal gas equation, the definition of density, and the relationship between number of moles and molar mass. You can then derive this equation when you need it. This approach proves that you understand the concepts and means one less equation to memorize. 

Start with the volume of N2, and change it to moles using density and molar mass. Then use the mole ratio followed by the molar mass of NaNs. 

Knowing the density and molar mass of a substance, we can readily compute its molar volume, that is, the volume occupied by one mole of a substance ... 

The ideal gas law can be rearranged to calculate the density and molar mass of a gas. In a mixture of gases, each component contributes its own partial pressure to the total pressure (Dalton s law of partial pressures). The mole fraction of each component is the ratio of its partial pressure to the total pressure. When a gas is in contact with water, the total pressure is the sum of the gas pressure and the vapor pressure of water at the given temperature. 

One very important use of the ideal gas law is in the calculation of the molar mass (molecular weight) of a gas from its measured density. To see the relationship between gas density and molar mass, consider that the number of moles of gas n can be expressed as... 

Perform the calculations necessary to demonstrate that bromine is indeed the limiting reagent (Sec. 1.6). The densities and molar mass needed to complete the calculations can be found in the abbreviated MSDSs on the website or various handbooks of chemistry. 

Thus, we can solve foe equation even though we are not given specific values for rr and V. We will examine how to use foe density and molar mass of a gas in this fashion in Section 10.5. 

Rearrangements of the ideal gas law are used to calculate the density and molar mass of a gas and the partial pressure of each gas in a gas mixture (Dalton s law). We use gas variables (P, V, and T) in stoichiometry problems to find the amounts (n) of gaseous reactants or products in a reaction. (Section 5.4)... 

At a given temperature and pressure, what mathematical relationship exists between the density and molar mass of a gas Explain your answer. 

The ideal gas equation can be used to calculate the density of a gas and to inteiconvetl between density and molar mass. 

We just examined how we can use the ideal gas law to calculate one of the variables (P, V,T, or n) given the other three. We now turn to three other applications of the ideal gas law molar volume, density, and molar mass. 

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