Chemical formulas as conversion factors

How many H2O molecules are in a sample of water with a mass of 3.64 g  

Compoimd A has a molar mass of 100 g/mol and Compound B has a molar mass of 200 g/mol. If you have samples of equal mass of both compounds, which sample contains the greatest number of molecules  

Like other conversion factors, this ratio gives the relationship between leaves and clovers. With this ratio, we can write a conversion factor to determine the number of leaves in 14 clovers. The solution map is  

We solve the problem by beginning with clovers and converting to leaves. 

Similarly, a chemical formula gives us ratios between elements and molecules for a particular compound. For example, the formula for carbon dioxide (CO2) means there are two O atoms per CO2 molecule. We write this as  

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To calculate the number of AP+ and Cl ions, use the ratios from the chemical formula as conversion factors. 

EXAMPLE 6.6 Chemical Formulas as Conversion Factors—Converting between Moles of a Compound and Moles of a Constituent Element... 

Composition of Compounds Chemical Formulas as Conversion Factors... 

Using Chemical Formulas as Conversion Factors (3.9) Example 3.16 For Practice 3.16 For More Practice 3.16 Exercises 83, 84... 

A mole of substance is the amount that contains Avogadro s number (6.022x10 ) of chemical entities (atoms, molecules, or formula units). The mass (in grams) of a mole has the same numerical value as the mass (in amu) of the entity. Thus, the mole allows us to count entitles by weighing them. Using the molar mass (jM., g/mol) of an element (or compound) and Avogadro s number as conversion factors, we can convert among amount (mol), mass (g), and number of entities. The mass fraction of element X in a compound is used to find the mass of X in any amount of the compound. 

Figure 3.8 Summary of the mass-mole-number relationships in a chemical reaction. The amount of one substance in a reaotion is related to that of any other. Quantities are expressed in terms of grams, moles, or number of entities (atoms, molecules, or formula units). Start at any box in the diagram (known) and move to any other box (unknown) by using the information on the arrows as conversion factors. As an example, if you know the mass (in g) of A and want to know the number of molecules of B, the path involves three calculation steps ...

Notice that we must convert from g NaCl to mol NaQ before we can use the chemical formula as a conversion factor. 

The coefficients in a chemical equation can be used as conversion factors in calculations much as the subscripts in a chemical formula were used previously. These calculations are important because they allow us to predict how much of a particular reactant might be needed in a particular reaction, or how much of a particular product will be formed. For example, one of the gases that contribute to global warming is carbon dioxide (COj). Carbon dioxide is a product of the combustion of fossil fuels such as methane, the primary component of natural gas. From the previous section, the chemical equation for the combustion of methane is as follows ... 

Notice that we must convert from g CCI2F2 to mol CCI2F2 before we can use the chemical formula as a conversion factor. Always remember that the chemical formula gives us a relationship between the amounts (in moles) of substances, not between the masses (in grams) of them. 

Exact numbers, such as the stoichiometric coefficients in a chemical formula or reaction, and unit conversion factors, have an infinite number of significant figures. A mole of CaCb, for example, contains exactly two moles of chloride and one mole of calcium. In the equality... 

For work in the laboratory, it s necessary to weigh reactants rather than just know numbers of moles. Thus, it s necessary to convert between numbers of moles and numbers of grams by using molar mass as the conversion factor. The molar mass of any substance is the amount in grams numerically equal to the substance s molecular or formula mass. Carrying out chemical calculations using these relationships is called stoichiometry. 

Stoichiometry is the series of calculations on the basis of formulas and chemical equations and will be covered in Chapter 4. The use of conversion factors is common even when the relative proportions are not fixed by a chemical formula. Consider a silver alloy used for jewelry production. (Alloys are mixtures of metals and, as mixtures, may be produced in differing ratios of the metals.) A particular alloy contains 86 percent silver. Factors based on this composition, such as... 

The chemical formula for a compound gives the ratio of atoms of each element in the compound to atoms of every other element in the compound. It also gives the ratio of dozens of atoms of each element in the compound to dozens of atoms of every other element in the compound. Moreover, it gives the ratio of moles of atoms of each element in the compound to moles of atoms of every other element in the compound. For example, a given quantity of H2O has 2 mol of H atoms for every mole of O atoms, and a given quantity of CH4 has 1 mol of C atoms for every 4 mol of H atoms. The mole ratio from the formula can be used as a factor to convert from moles of any element in the formula to moles of any other element or to moles of the formula unit as a whole. In Figure 7.2, these additional conversions have been added to those already presented in Figure 7.1. 

Conversion factors such as the one just used for fluorine can he written for any element in a compound. The number of moles of the element that goes in the numerator of the conversion factor is the subscript for that element in the chemical formula. 

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. 

The necessary basic knowledge is provided in Chapter 2 The Chemical Production Plant and its Components. It deals vhth important subdisciplines of technical chemistry such as catalysis, chemical reaction engineering, separation processes, hydrodynamics, materials and energy logistics, measurement and control technology, plant safety, and materials selection. Thus, it acts as a concise textbook vhthin the book that saves the reader from consulting other works when such information is required. A comprehensive appendix (mathematical formulas, conversion factors, thermodynamic data, material data, regulations, etc.) is also provided. 

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