Atomic and molar masses

Any atom has a tiny nucleus, diameter m, in the center ofa relatively enormous electron cloud, diameter m. The negative charge of the electron cloud exactly 

The isotope of carbon with mass number 12 has been chosen as the defining element for the scale of atomic masses. We define the atomic mass unit, symbol u, as exactly 1/12 of the mass of one atom of carbon-12. Then u = 1.6605655 x 10 kg. The relative atomic mass ofanatom, Ar,is defined by A = m/u, where mis the mass of the atom for example, AXiH) = 1.007825 AJ[ C) = 12 (exactly) = 15.99491. In any macroscopic 

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Absolute measurements by fundamental quantities like Faraday constant and quotients of atomic and molar masses, respectively (coulom-etry, electrogravimetry, gravimetry, gas volumetry)... 

The general designation (i.e., chemical name, CAS registry number, UN number), the relative atomic and molar mass, the physical properties (i.e., density, viscosity), thermal properties (i.e., molar heat capacities, latent enthalpies, and thermal conductivity), optical properties (e.g., refractive index), along with properties important for health and safety (i.e., flammability limits, ignition temperature, toxicity) of some important gases are reported in Tables 19.15-19.17. 

Notice that atomic mass and the molar mass of carbon-12 are numerically equal. They differ only in units atomic mass is measured in atomic mass units, and molar mass is measured in grams per mole. The same relationships exist between atomic and molar masses of elements, between molecular masses and molar masses of molecular substances, and between formula masses and molar masses of ionic compounds. In other words,... 

Within the wide range of phosphorus compounds described as activating agents for polyesterification reactions,2,310 triphenylphosphine dichloride and diphenylchlorophosphate (DPCP) were found to be the most effective and convenient ones. In pyridine solution, DPCP forms a A-phosphonium salt which reacts with the carboxylic acid giving the activated acyloxy A -phosphonium salt. A favorable effect of LiBr on reaction rate and molar masses has been reported and assumed to originate from the formation of a complex with the A-phosphonium salt. This decreases the electron density of the phosphorus atom... 

Unlike the case with dilute solutions of polymer, the variation of the melt viscosity and molar mass is far from completely understood. However, the melt viscosity, has been found to vary uniformly with number of carbon atoms in the chain above about 300-500, according to the equation ... 

Avogadro s number and molar mass make it possible to convert readily among the mass of a pure element, the number of moles, and the number of atoms in the sample. These conversions are represented schematically in the flowchart shown in Figure 2-22. 

Hydrogen phthalate has one acidic hydrogen atom. As the net reaction shows, there is a 1 1 molar ratio between hydrogen phthalate and hydroxide HCg Hq O4 + OH Cg Hq O4 + H2 O The number of moles of hydrogen phthalate anions is the same as the number of moles of KHCg Hq Oq, which is calculated from its mass and molar mass ... 

Analyze each pair, keeping in mind that several features affect absolute entropy, including phase, number of atoms or molecules, amount of bonding, and molar mass. 

The greatest number of S atoms is contained in the compound with the greatest number of moles of S. The solid sulfur contains 8x0.12mol = 0.96 mol S atoms. There are 0.50x2 mol S atoms in 0.50 mol S20. There is slightly greater than 1 mole (64.1 g) of S02 in 65 g, and thus a bit more than 1 mole of S atoms. The molar mass of thiophene is ... 

Introduction and Orientation, Matter and Energy, Elements and Atoms, Compounds, The Nomenclature of Compounds, Moles and Molar Masses, Determination of Chemical Formulas, Mixtures and Solutions, Chemical Equations, Aqueous Solutions and Precipitation, Acids and Bases, Redox Reactions, Reaction Stoichiometry, Limiting Reactants... 

Older books and chemical journals used the terms atomic weight and molecular weight rather than atomic mass and molar mass. Because "weight" is a force rather than a mass, such usage is potentially confusing and is now discouraged, but many chemists trained in an earlier time still use the old terms, so you may encounter them. 

CHAPTER 2 Atomic and Molecular Mass Molar Mass 16... 

Table 5.2 Average Atomic Mass and Molar Mass of Four Elements...

How do chemists use the mole and molar masses to count numbers and relative numbers of atoms and molecules Relate your answer to the techniques you used to count rice, nuts, and washers. 

O Draw a diagram that shows the relationship between the atomic mass and molar mass of an element and the Avogadro constant. 

Explain how the Avogadro constant, average atomic mass, and molar mass are related. 

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. 

The percentage of mass in an element in a compound can easily be found when the molecular formula and molar mass (or atomic mass) of elements are known. 

Scientists also use the simplest formula to represent one mole of an ionic compound. They often use the term formula unit when referring to ionic compounds, because they are not found as single molecules. A formula unit of an ionic compound represents the simplest ratio of cations to anions. A formula unit of KBr is made up of one ion and one Br ion. One mole of an ionic compound has 6.022 x 10 of these formula units. As with molecular compounds, the molar mass of an ionic compound is the sum of the masses of all the atoms in the formula expressed in g/mol. Table 1 compares the formula units and molar masses of three ionic compounds. Sample Problem F shows how to calculate the molar mass of barium nitrate. 

For an element, what is the relationship between atomic mass and molar mass ... 

Use the following terms to create a concept map atoms, average atomic mass, molecules, mole, percentage composition, and molar masses. 

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