The Mole and Molar Masses

F ig u re 3.2 One mole each of some familiar substances left) sulfur, middle) iron, right) mercury, and in balloon) helium. 

Note also that the subscripts in a chemical formula denote the ratio of combination of atoms in a substance. Just as a water molecule contains two H atoms and one O atom, a mole of water molecules contains two moles of H atoms and one mole of O atoms. The ratio of combination stays the same, regardless of the size of the sample. 

Sample Problem 3.5 lets you practice converting between moles and atoms. 

Think About It Make sure that units cancel properly in each solution and that the result makes sense. In part (a), for example, the number of moles (30) is greater than one, so the number of atoms is greater than Avogadro s number. In part (b), the number of atoms (lx 10 ) is less than Avogadro s number, so there is less than a mole of substance. 

Calcium is the most abundant metal in the human body. A typical human body contains roughly 30 moles of calcium. Determine (a) the number of Ca atoms in 30.00 moles of calcium and (b) the number of moles of calcium in a sample containing 1.00 X 10 ° Ca atoms. 

Avogadro number is almost unimaginably big. If 6.022 X 10 pennies were distributed equally among every inhabitant of the United States, each man, woman, and child would have over 20 trillion dollarsi Furthermore, each persons share of pennies, neatly stacked, would occupy approximately the same volume as 760 Empire State Buildings. 

Strategy Use Avogadro s number to convert from moles to atoms and from atoms to moles. 

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How can you use what you know about the mole and molar mass to count large numbers of tiny objects using mass, and to relate numbers of objects you cannot see based on their masses ... 

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. 

You will use the mole and molar mass to make conversions among moles, mass, and number of representative particles. 

IBLG See questions from The Mole and Molar Mass ... 

The definitions of atomic mass, the mole, and molar mass are all directly or indirectly related to carbon-12. This leads to two important facts ... 

In Section 3.2, we learned how to use the chemical formula (either molecular or empirical) to determine the percent composition by mass. With the concepts of the mole and molar mass, we can now use the experimentally determined percent composition to determine the empirical formula of a compoimd. Sample Problem 3.8 shows how to do this. 

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... 

Now, the mass of NaCI needed can be found by using the relationship between moles and molar mass mol = mass/ Molar Mass... 

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. 

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 ... 

From the number of moles and molar masses of reactants and products, the following desired masses are found ... 

Determine the number of moles present using the molar mass conversion 1 mol = molar mass of substance. Put the 1 mol on the top of the fraction and molar mass on the bottom of the fraction so that the grams of the substance cancel and the answer is in moles of the 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. 

The answer is A. Density is equal to mass per volume. Further more, the mass is equal to the product of number moles and molar mass. Equating these two equations we can get the answer. Using the letter notations given in the question, the expression of volume is given by Choice A. 

Chapter 7, Chemical Quantities and Reactions, introduces moles and molar masses of compounds, which are used in calculations to determine the mass or number of particles in a given quantity. Students leam to balance chemical equations and to recognize the types of chemical reactions combination, decomposition, single replacement, double replacement, and combustion reactions. Section 7.5 discusses Oxidation-Reduction Reactions using real-life examples, including biological reactions. Section... 

In Chapter 13, you learned how to use moles and molar mass along with a balanced chemical equation to calculate the masses of reactants and products in a chemical reaction. Now that you know how to relate volumes, masses, and moles for a gas, you can do stoichiometric calculations for reactions involving gases. 

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. 

C03-0041. Write a paragraph that defines molar mass, mole, and molarity and explains the differences among them. 

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 ... 

To convert between molarity and the other mole-based concentration measures, we must relate volume to mass and number of moles. Whereas molar mass lets us convert between mass and moles, we need density to convert... 

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