Stoichiometry formula weights

As can be seen from equation 8.14, we may improve a method s sensitivity in two ways. The most obvious way is to increase the ratio of the precipitate s molar mass to that of the analyte. In other words, it is desirable to form a precipitate with as large a formula weight as possible. A less obvious way to improve the calibration sensitivity is indicated by the term of 1/2 in equation 8.14, which accounts for the stoichiometry between the analyte and precipitate. Sensitivity also may be improved by forming precipitates containing fewer units of the analyte. 

In a stoichiometry calculation, the weight of one substance involved in a chemical reaction (reactant or product) is converted to the weight of another substance (reactant or product) appearing in the same reaction. The balanced equation is the basis for the calculation, and the formula weights of the reactant and product involved are needed. In the following general example,... 

A stoichiometry calculation is thus essentially a three-step procedure in which 1) the weight of D is divided by its formula weight to get moles of D, 2) the moles of D are converted to the moles of A by multiplying by the mole ratio a/d, as found in the chemical equation, and 3) the moles of A are converted to grams of A by multiplying by the formula weight of A. 

Fig. 2. Stoichiometry of aluminum removal from Na-Y by H4/EDTA. FW formula weight, NaA102(Si02)y [24]...

An elemental material balance approach to growth stoichiometry requires an empirical formula for dry weight material ... 

The same mole ratio, a/d, can also be found by simply balancing the common element in the formulas of A and D. Thus, the ratio, a/d, is the same as the ratio QS/QK seen in the equation for a gravimetric factor derived in Section 3.6.3 (Equation (3.12)) and is used to convert the weight of one substance to the weight of another, just as we described in Chapter 3 was the purpose of the gravimetric factor. Thus the concept of a gravimetric factor is based on stoichiometry. 

A chemical formula tells the numbers and the kinds of atoms that make up a molecule of a compound. Because each atom is an entity with a characteristic mass, a formula also provides a means for computing the relative weights of each kind of atom in a compound. Calculations based on the numbers and masses of atoms in a compound, or the numbers and masses of molecules participating in a reaction, are designated stoichiometric calculations. These weight relationships are important because, although we may think of atoms and molecules in terms of their interactions as structural units, we often must deal with them in the lab in terms of their masses—with the analytical balance. In this chapter, we consider the Stoichiometry of chemical formulas. In following chapters, we look at the stoichiometric relations involved in reactions and in solutions. 

Stoichiometric The characteristic proportions of chemical reaction, obtained from chemical formulae, equations, atomic weights and molecular weights. Stoichiometry determines what and how much is used and produced in a chemical process. 

A theoretical model of the combustion of biomass is illustrated by the complete oxidation of giant brown kelp. Note that kelp, for which complete analytical data were available, is used here simply to illustrate the utility of the model, which is applicable to all biomass species. Based on the empirical formula derived from the elemental analysis of dry kelp at an assumed molecular weight of 100, the combustion stoichiometry is... 

This formula relates the ultimate possible molecular weight to the initial stoichiometry. A few values are... 

The Power of Connectivity—Stoichiometry The last two formulae of sand, [Si02loo or simply Si02, show that Si and O combine in an atomic ratio of 1 2. Thus, even though the molecule may have zillions of atoms, still the basic ratio of the two constituents remains 1 2. Ever since Lavoisier showed the power of quantitative analysis in chemistry and defined the notion of an element as a simple body, chemists tried to find quantitative relationships between the combined weights... 

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