Chemical formulas percent composition from

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... 

Elemental analysis is the cornerstone of all chemical inquiry. Almost before one asks what is it , one asks what is its percent composition . From such data, a chemist writes the first empirical formula, and later a molecular formula. If the substance is very similar to a known compound, the chemist may well infer that it is a simple modification of the molecular formula. Or, if the unknown substance is extracted from a plant or microorganism, an educated guess about its structure may be made, based on the formulas of other compounds extracted from the same source. 

Mass Percent Composition from a Chemical Formula 181... 

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... 

In Section 6.7, we learned how to calculate mass percent composition from a chemical formula. But can we go the other way Can we calculate a chemical formula from mass percent composition This is important because laboratory analyses of compounds do not often give chemical formulas directly rather, they give the relative masses of each element present in a compound. For example, if we decompose water into hydrogen and oxygen in the laboratory, we could measure the masses of hydrogen and oxygen produced. Can we determine a chemical formula for water from this kind of data ... 

What is the mathematical formula for calculating mass percent composition from a chemical formula How are the empirical formula and the molecular formula of a compound related ... 

MASS PERCENT COMPOSITION FROM CHEMICAL FORMULA ... 

STRATEGIZE The molecular formula teUs you that there are 4 mol of Cl in each mole of Freon-112. Find the mass percent composition from the chemical formula by using the equation that defines mass percent. The conceptual plan shows you how to use the mass of Cl in 1 mol of C2CI4F2 and the molar mass of C2CI4F2 to find the mass percent of Cl. CONCEPTUAL PLAN, , 4 X molar mass Cl, Mass % Cl = X 100% molar mass C2CI4F2 RELATIONSHIPS USED mass of element X in 1 mol of compound Mass percent of element X — — X 100% mass of 1 mol of compound... 

In the problem above, we determined the percentage data from the chemical formula. We can determine the empirical formula if we know the percent compositions of the various elements. 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. However, the procedure is still the same—convert each element to moles, divide each by the smallest, and then use an appropriate multiplier if necessary. We can then determine the empirical formula mass. If we know the actual molecular mass, dividing the molecular formula mass by the empirical formula mass, gives an integer (rounded if needed) that we can multiply each of the subscripts in the empirical formula. This gives the molecular (actual) formula, which tells what elements are in the compound and the actual number of each. 

Be able to calculate the empirical formula from percent composition data or quantities from chemical analysis. 

In the previous section the problems presented a chemical formula and asked for the percent composition. There is a method for going from percent composition to chemical formula however, you will obtain only the empirical formula from this. The three steps in determining the empirical formula of a compound from the percent composition are as follows ... 

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. 

For analysis of the differences between incineration with air and oxygen a reference chemical formula for solid waste was generated. Much of the waste is paper and plant refuse composed primarily of cellulose. Plastic, fats and grease, as well as a small amount of protein, were included. Water was included since most waste is damp. Small amounts of chlorine from plastics such as vinyl chloride, and sulfur from protein and rubber were included. Table 8.1 A shows the amounts (in weight percent) of components of the reference waste. Table 8.IB shows the elemental chemical composition of the reference waste derived from the components. 

Percent composition can be determined from the chemical formula of a compound. 

Empirical Formula from Percent Composition Methyl acetate is a solvent commonly used in some paints, inks, and adhesives. Determine the empirical formula for methyl acetate, which has the following chemical analysis ... 

Chemical stoichiometry is the area of study that considers the quantities of materials in chemical formulas and equations. Quite simply, it is chemical arithmetic. The word itself is derived from stoicheion, the Greek word for element and metron, the Greek word for measure. When based on chemical formulas, stoichiometry is used to convert between mass and moles, to calculate the number of atoms, to calculate percent composition, and to interpret the mole ratios expressed in a chemical formula. Most topics in chemical arithmetic depend on the interpretation of balanced chemical equations. Mass/mole conversions, calculation of limiting reagent and percent yield, and various relationships among reactants and products are commonly included in this topic area. 

When a new molecule is synthesized, an elemental analysis is routinely performed to help verify its identity. This test, which measures the mass percentage of each element in the compound, is also Ifequendy done as part of the process of identifying any substance whose composition is unknown. The mass percentages describe the compound s composition, and so they must be related to its chemical formula. But the data obtained from elemental analysis describe the composition in terms of the mass of each element, whereas the formula describes the composition in terms of the number of atoms of each element. So these are two different representations of very similar information, and the molar masses of the elements provide a connection between them. The process of obtaining the empirical formula of a compound from its percent composition by mass is best illustrated by an example. 

To continue our study of moleeules and ionic compounds, we leam how to calculate the percent composition of these species from their chemical formulas. (3.5)... 

Knowing the chemical formula and the molecular mass of a compound enables us to calculate the percent composition by mass—the percent by mass of each element in a compound. It is useful to know the percent composition by mass if, for example, we needed to verify the purity of a compound for use in a laboratory experiment. From the formula we could calculate what percent of the total mass of the compound is contributed by each element. Then, by comparing the result to the percent composition obtained experimentally for our sample, we could determine the purity of the sample. Mathematically, the percent composition is obtained by dividing the mass of each element in 1 mole of the compound by the molar mass of the compound and multiplying by 100 percent ... 

We just learned how to go from the chemical formula of a compound to its mass percent composition. Can we also go the other way ... 

One way to express how much of an element is in a given compound is to use the element s mass percent composition for that compound. The mass percent composition or mass percent of an element is that element s percentage of the compound s total mass. We can calculate the mass percent of element X in a compound from the chemical formula as follows ... 

With ratios such as these—which come from the chemical formula—we can directly determine the amounts of the constituent elements present in a given amount of a compound without having to calculate mass percent composition. For example, we calculate the number of moles of Cl in 38.5 mol of CCI2F2 as follows ... 

The mass percent composition of a compound indicates each element s percentage of the total compound s mass. The mass percent composition can be determined from the compound s chemical formula and the molar masses of its elements. 

At times, a chemist isolates a chemical compound—say, from an exotic tropical plant—and has no idea what it is. A report from an analytical laboratory on the percent composition of the compound yields data needed to determine its formula. 

Percent composition establishes the relative proportions of the elements in a compound on a mass basis. A chemical formula requires these proportions to be on a mole basis, that is, in terms of numbers of atoms. Consider the following five-step approach to determining a formula from the experimentally determined percent composition of the compound 2-deoxyribose, a sugar that is a basic constituent of DNA (deoxyribonucleic acid). The mass percent composition of 2-deoxyribose is 44.77% C, 7.52% H, and 47.71% O. 

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