Mole concept molarity

Students will explain the mole concept and use this concept to prepare chemical solutions of particular molarities. 

This chapter is about states of matter and a section of chemistry called thermo-dynamics, which is the inspiration (or lack thereof) for the chapter title. Some of what is in this chapter might seem just a bit disconnected from the content in the rest of the book, but it s an important part of chemistry and helps introduce the equally important concepts of moles and molarity. The best way to introduce those concepts is to start with how gases behave. You also need a basic understanding of the states of matter. If you have read the Stop Faking It book Air, Water, and Weather, you will recognize some of the activities in this chapter. Before skipping over those, you should know that the explanations that follow will not be identical to those in the other book. atoms Is that the best title you... 

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. 

Concept Mapping Design a concept map that illustrates the mole concept. Include moles, Avogadro s number, molar mass, number of particles, percent composition, empirical formula, and molecular formula. 

Gas laws, including the ideal gas law, Dalton s law, and Graham s law Stoichiometric relations using the concept of the mole titration calculations Mole fractions molar and molal solutions... 

Review the following concepts before studying this chapter. Chapter 12 the mole concept using the factor label method Chapter 13 solution concentration using molarity... 

A basic question raised in the chemical laboratory is, How much product will be formed from specific amounts of starting materials (reactants) Or in some cases we might ask the reverse question How much starting material must be used to obtain a specific amount of product To interpret a reaction quantitatively, we need to apply our knowledge of molar masses and the mole concept. Stoichiometry is the quantitative study of reactants and products in a chemical reaction. 

The mole concept is useful in expressing concentrations of solutions, especially in analytical chemistry, where we need to know the volume ratios in which solutions of different materials will react. A one-molar solution is defined as one that contains one mole of substance in each liter of a solution. It is prepared by dissolving one mole of the substance in the solvent and diluting to a final volume of one liter in a volumetric flask or a faction or multiple of the mole may be dissolved and diluted to the corresponding fraction or multiple of a hter (e.g., 0.01 mol in 10 mL). More generally, the molarity of a solution is expressed as moles per liter or as millimoles per milliliter. Molar is abbreviated as M, and we talk of the molarity of a solution when we speak of its concentration. A one-molar solution of silver nitrate and a one-molar solution of sodium chloride will react on an equal-volume basis, since they react in a 1 1 ratio Ag + Cl —> AgCl. We can be more general and calculate the moles of substance in any volume of the solution. 

Realize the usefulness of the mole concept, and use the relation between molecular (or formula) mass and molar mass to calculate the molar mass of any substance ( 3.1) (EPs 3.1-3.5, 3.7-3.10)... 

As we learned in Section 2.6, the empirical formula for a substance tells us the relative number of atoms of each element in the substance. The empirical formula H2O shows that water contains two H atoms for each O atom. This ratio also applies on the molar level 1 mol of H2O contains 2 mol of H atoms and 1 mol of O atoms. Conversely, the ratio of the numbers of moles of all elements in a compound gives the subscripts in the compound s empirical formula. Thus, the mole concept provides a way of calculating empirical formulas. 

Molarity is the concentration unit most often used by chemists, because it utilizes moles. The mole concept is central to chemistry, and molarity lets chemists easily work solutions into reaction stoichiometry. (U you re cussing me out right now because you have no idea what burrowing, insect-eating mammals have to do with chemistry, let alone what stoichiometry is, just flip to Chapter 10 for the scoop. Your mother would probably recommend washing your mouth out with soap first.)... 

The Mole Concept Avagadro s Number and the Molar Mass of an Element... 

When solution concentrations are expressed as molarities, the mole concept can be applied to reactions taking place between substances that are solutes in the solutions. 

The Mole Concept The mole is a specific number (6.022 X 10 ) that allows us to easily coimt atoms or molecules by weighing them One mole of any element has a mass equivalent to its atomic mass in grams, and a mole of any compoimd has a mass equivalent to its formula mass in grams. The mass of 1 mol of an element or compound is its molar mass. 

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. 

Molar mass and the Avogadro constant are used in a variety of calculations involving the mass, amount (in moles), and number of atoms in a sample of an element. Other conversion factors may also be involved in these calculations. The mole concept is encountered in ever broader contexts throughout the text. 

The Mole Concept and Chemical Compounds—In this section, the concept of atomic mass is extended to molecular mass, the mass in atomic mass units of a molecule of a molecular compound, and formula mass, the mass in atomic mass units of a formula unit of an ionic compound. Likewise, the concept of the Avogadro constant and the mole is now applied to compounds, with emphasis on quantitative applications involving the mass of a mole of compound— the molar mass M. For several elements, we can distinguish between a mole of molecules (for example, P4) and a mole of atoms (that is, P). 

The system is ideal, with equilibrium described by a constant relative volatility, the liquid components have equal molar latent heats of evaporation and there are no heat losses or heat of mixing effects on the plates. Hence the concept of constant molar overflow (excluding dynamic effects) and the use of mole fraction compositions are allowable. 

When reporting the molar conductivity data, the species whose amount is given in moles should be indicated. Often, a fractional molar conductivity corresponding to one mole of chemical equivalents (called a val) is reported. For example, for sulphuric acid, the concentration c can be expressed as the normality , i.e. the species H2S04 is considered. Obviously, A(H2S04) = 2A( H2S04). Consequently, the concept of the equivalent conductivity is often used, defined by the relationship... 

Background This experiment uses the concept of continuous variation to determine mass and mole relationships. Continuous variation keeps the total volume of two reactants constant, but varies the ratios in which they combine. The optimum ratio would be the one in which the maximum amount of both reactants of known concentration are consumed and the maximum amount of product(s) is produced. Since the reaction is exothermic, and heat is therefore a product, the ratio of the two reactants that produces the greatest amount of heat is a function of the actual stoichiometric relationship. Other products that could be used to determine actual molar relationships might include color intensity, mass of precipitate formed, amount of gas evolved, and so on. 

The most important concept when working stoichiometry problems such as this one is moles. We must have moles to proceed. The mole determination of iodine will involve the molar mass of iodine (2 x 126.9 g/mol), while the mole determination of fluorine will involve Avogadro s number (since we have number of fluorine molecules). We can find the moles of each as follows ... 

The number of molecules passing in each direction from vapour to liquid and in reverse is approximately the same since the heat given out by one mole of the vapour on condensing is approximately equal to the heat required to vaporise one mole of the liquid. The problem is thus one of equimolecular counterdiffusion, described in Volume 1, Chapter 10. If the molar heats of vaporisation are approximately constant, the flows of liquid and vapour in each part of the column will not vary from tray to tray. This is the concept of constant molar overflow which is discussed under the heat balance heading in Section 11.4.2. Conditions of varying molar overflow, arising from unequal molar latent heats of the components, are discussed in Section 11.5. 

The fact that both the mole and the mass of an element are based on carbon-12 enables us to relate mole and mass. A molar mass is defined as the mass in grams of one mole of a substance, and it can be obtained directly from an element s atomic mass. We can use the elements hydrogen and nitrogen to illustrate this concept. Periodic table entries for both elements are shown below. The whole number above the element is the atomic number and gives the number of protons in the nucleus. The number below the element s symbol is the molar mass (as well as the atomic mass) ... 

The relative partial molar enthalpies of the species are obtained by using Eqs. (70) and (75) in Eq. (41). When the interaction coefficients linear functions of T as assumed here, these enthalpies can be written down directly from Eq. (70) since the partial derivatives defining them in Eq. (41) are all taken at constant values for the species mole fractions. Since the concept of excess quantities measures a quantity for a solution relative to its value in an ideal solution, all nonzero enthalpy quantities are excess. The total enthalpy of mixing is then the same as the excess enthalpy of mixing and a relative partial molar enthalpy is the same as the excess relative partial molar enthalpy. Therefore for brevity the adjective excess is not used here in connection with enthalpy quantities. By definition the relation between the relative partial molar entropy of species j, Sj, and the excess relative partial molar entropy sj is... 

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