Compounds calculating chemical formulas used

Knowing a compound s percent composition makes it possible to calculate the compound s chemical formula. As shown in Figure 3.8, the strategy is to find the relative number of moles of each element in the compound and then use the numbers to establish the mole ratios of the elements. The mole ratios, in turn, give the subscripts in the chemical formula. 

The number of moles of an element in a mole of componnd can also be used to calculate the number of moles of the compound involved in a reaction. The ratio of the number of moles of an element within a compound to the number of moles of the compound is determined by the compound s chemical formula (Section 7.3). Thns, the snbscripts of the formula may be used to form conversion factors. 

In the problems above, the percentage data was calculated from the chemical formula, but the empirical formula can be determined if the percent compositions of the various elements are known. The empirical formula tells us what elements are present in the compound and the simplest whole-number ratio of elements. The data may be in terms of percentage, or mass, or even moles. But the procedure is still the same convert each to moles, divide each by the smallest number, then use an appropriate multiplier if needed. The empirical formula mass can then be calculated. If the actual molecular mass is known, dividing the molecular mass by the empirical formula mass gives an integer (rounded if needed) that is used to multiply each of the subscripts in the empirical formula. This gives the molecular (actual) formula, which tells which elements are in the compound and the actual number of each. 

In terms of the visual clarity of its presentation, biochemistry has still to catch up with anatomy and physiology. In this book, we sometimes use simplified ball-and-stick models instead of the classical chemical formulae. In addition, a number of compounds are represented by space-filling models. In these cases, we have tried to be as realistic as possible. The models of small molecules are based on conformations calculated by computer-based molecular modeling. In illustrating macromolecules, we used structural infor-... 

If we know the chemical composition of a compound, we can calculate the empirical formula for it. An empirical formula is the simplest formula using the smallest set of integers to express the ratio of atoms present in a molecule. 

In the previous Practice Problems, you used mass data to calculate percentage composition. This skill is useful for interpreting experimental data when the chemical formula is unknown. Often, however, the percentage composition is calculated from a known chemical formula. This is useful when you are interested in extracting a certain element from a compound. For example, many metals, such as iron and mercury, exist in mineral form. Mercury is most often found in nature as mercury(II) sulfide, HgS. Knowing the percentage composition of HgS helps a metallurgist predict the mass of mercury that can be extracted from a sample of HgS. 

If you assume that you have one mole of a compound, you can use the molar mass of the compound, with its chemical formula, to calculate its percentage composition. For example, suppose that you want to find the... 

In the previous section, you learned how to calculate the percentage composition of a compound from its chemical formula. Now you will do the reverse. You will use the percentage composition of a compound, along with the concept of the mole, to calculate the empirical formula of the compound. Since the percentage composition can often be determined by experiment, chemists use this calculation when they want to identify a compound. 

The meaning of a chemical formula was discussed in Chapter 5, and we learned how to interpret formulas in terms of the numbers of atoms of each element per formula unit. In this chapter, we will learn how to calculate the number of grams of each element in any given quantity of a compound from its formula and to do other calculations involving formulas. Formula masses are presented in Section 7.1, and percent composition is considered in Section 7.2. Section 7.3 discusses the mole—the basic chemical quantity of any substance. Moles can be used to count atoms, molecules, or ions and to calculate the mass of any known number of formula units of a substance. Section 7.4 shows how to use relative mass data to determine empirical formulas, and the method is extended to molecular formulas in Section 7.5. 

In Chapter 7, we learned how to do nnmerical calculations for compounds, using their formulas as a basis. This chapter lays the foundation for doing similar calculations for chemical reactions, using the balanced equation as a basis. The chemical equation is introduced in Section 8.1, and methods for balancing equations are presented in Section 8.2. To write equations, we must often be able to predict the products of a reaction from a knowledge of the properties of the reactants. Section 8.3 shows how to classify chemical reactions into types to predict the products of thousands of reactions. An important type of reaction— the acid-base reaction— is discussed in Section 8.4. 

The balanced chemical equation gives the mole ratios of all the substances in the reaction, just as an empirical formula gives the ratios of atoms of the elements in a compound. As with chemical formulas, these ratios can be used as factors in calculations involving any two of the substances. 

The graphing calculator can run a program that calculates the molar mass of a compound given the chemical formula for the compound. This program will prompt for the number of elements in the formula, the number of atoms of each element in the formula, and the atomic mass of each element in the formula. It then can be used to find the molar masses of various compounds. 

The mass of your backpack is the sum of the mass of the pack plus the masses of the books, notebooks, pencils, lunch, and miscellaneous items you put into it. You could find its mass by determining the mass of each item separately and adding them together. Similarly, the mass of a mole of a compound equals the sum of the masses of every particle that makes up the compound. You know how to use the molar mass of an element as a conversion factor in calculations. You also know that a chemical formula indicates the number of moles of each element in a compound. With this information, you can now determine the molar mass of a compound. 

Percent composition from the chemicai formuia If you already know the chemical formula for a compound such as water (H2O), can you calculate its percent composition The answer is yes. You can use the chemical formula to calculate the molar mass of water (18.02 g/mol) and assume you have an 18.02-g sample. Because the percent composition of a compound is always the same, no matter the size of the sample, you can assume that the sample... 

The data used to determine the chemical formula for a compound may be in the form of percent composition or it may be the actual masses of the elements in a given mass of the compound. If percent composition is given, you can assume that the total mass of the compound is 100.00 g and that the percent by mass of each element is equal to the mass of that element in grams. For example, the percent composition of an oxide of sulfiir is 40.05% S and 59.95% O. Thus, as you can see in Figure 11-10, 100.00 g of the oxide contains 40.05 g S and 59.95 g O. The mass of each element can be converted to a number of moles by multiplying by the inverse of the molar mass. Recall that the number of moles of S and O are calculated in this way. 

An average molecular mass (weight) of the polymer also needs to be defined, since components of various molecular masses (weights) M, are present in the polymer. The number of moles of species i in the polymer can be obtained from the typical formula ni = W] / Mi where W is the weight fraction of the component i", and M, is the molecular mass of species i . The masses of molecules or groups can be calculated using two different conventions. One convention considers the natural isotopic abundance of elements and takes their sum based on the compound chemical formula. For the masses of polymers, the first convention is typically used. The other convention considers only the masses of the most abundant isotope, which is useful for MS... 

Only K, B, H, S and R were used as sourees of data for simple oxides, oxohydroxides and hydroxides. Specialized databases created primarily for mineralogists and geologists report on thermodynamic data for materials of their special interest, e.g. natural silicates and aluminosilicates. These databases were used to complete data which were not available in K, B, H, S or R. Ref. [14] abbreviated as C does not directly list G° or AGf values. The G° values were calculated from Eq. (2.28) using the S taken from C. Then, Eq. (2.26) was applied to calculate AGf (compound) and the values of G° (elements) were taken from K. Then, data from Ref, [15] abbreviated as P were used. A few chemical formulas in P have typographical errors, which have been corrected in Table 2.2. The G° values were... 

We have just shown that a knowledge of the chemical formula allows us to calculate the elemental percentage composition of a compound. In the laboratory it is more common to analyze a compound and determine its percentage composition by experimental means. This information is then used to calculate the simplest formula and molecular formula of the compound. 

The solubility of sparingly soluble compounds that do not appear in this table may be calculated from the data in the table Solubility Product Constants . Solubility of inorganic gases may be found in the table Solubility of Selected Gases in Water Compounds are listed alphabetically by chemical formula in the most commonly used form (e.g., NaCl, NH NO, etc.). 

The molar mass of a compound can be calculated from its chemical formula and can be used to convert from mass to moles of that compound. 

By input compounds names or chemical formulas to RPS, suitable descriptors for the compounds group desired are calculated with the same procedures as in the main function of RPS by the computer and then capacity factor s for the solutes at v u ious mobile phase compositions are predicted by step-by-step with the interval of X=0.01 for both aqueous acetonitrile and methanol mobile phases. The range available in this procedure is from 0.3 to 0.7 of X-values for acetonitrile system and from 0.4 to 0.8 for methanol system, respectively. After calculations of capacity factors for the desired solutes, Rgand Tp, for each step are estimated according to the equation-9 and 10, at five different flow rates of the mobile phase such as 1, 2, 4, 8 and 16 uL/min (because we use microcolumns) and then quality of the separation is Judged using a simple numerical chromatographic response function (CRF) defined as follows ... 

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