Percent Composition as a Conversion Factor

The mass percent composition of an element in a compound is a conversion factor between mass of the element and mass of the compound. For example, we saw that the mass percent composition of Cl in CCI2F2 is 58.64%. Since percent means per hundred, there are 58.64 g Cl per hundred grams CCI2F2, which can be expressed as the ratio  

These ratios can function as conversion factors between grams of Cl and grams of CCI2F2. For example, to calculate the mass of Cl in 1.00 kg CCI2F2, we use the following conceptual plan  

Notice that the mass percent composition acts as a conversion factor between grams of the compound and grams of the constituent element. To calculate grams Cl, we follow the conceptual plan. 

EXAMPLE 3.15 Using Mass Percent Composition as a Conversion Factor 

Food and Drug Administration (FDA) recommends that a person consume less than 2.4 g of sodium per day. What mass of sodium chloride (in grams) can you consume and still be within the FDA guidelines Sodium chloride is 39% sodium by mass. 

---

In the previous section, we learned how to calculate mass percent composition from experimental data and how to use mass percent composition as a conversion factor. We can also calculate the mass percent of any element in a compound from the chemical formula for the compound. Based on the chemical formula, the mass... 

STRATE6IZE Convert between mass of a constituent element and mass of a compound by using mass percent composition as a conversion factor. 

Using Mass Percent Composition as a Conversion Factor (3.9) Example 3.15 For Practice 3.15 For More Practice 3.15 Exercises 77, 78... 

Mass percent composition can be used as a conversion factor between grams of a constituent element and grams of the compound. Write the conversion factor (including units) inherent in each mass percent composition. 

Density and Percent Composition Their Use in Problem Solving—Mass and volume are extensive properties they depend on the amount of matter in a sample. Density, the ratio of the mass of a sample to its volume, is an intensive property, a property independent of the amount of matter sampled. Density is used as a conversion factor in a variety of calculations. 

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... 

---