Chemical formulas percentage composition from

Answers (a) aluminum, sulfur, and oxygen (b) 2,3 (c) 1,4 (d) 2,3,12. Percentage Composition from Chemical Formulas 

The percentage of each element in glucose is given as follows  

Example What is the percentage elemental composition of calcium oxalate, 

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Calculating Percentage Composition from a Chemical Formula... 

If you know the chemical formula of any compound, then you can calculate the percentage composition. From the subscripts, you can determine the mass contributed by each element and add these to get the molar mass. Then, divide the mass of each element by the molar mass. Multiply by 100 to find the percentage composition of that element. 

If the chemical formula of a compound is already known, its mass percentage composition can be obtained from the formula. 

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. 

F.3 Determine the chemical formulas from the following analyses, (a) The mass percentage composition of cryolite, a compound used in the production of aluminum, is 32.79% Na, 13.02% Al, and 54.19% F. 

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. 

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. 

Scientists synthesize new compounds for many uses. Once they make a new product, they must check its identity. One way is to carry out a chemical analysis that provides a percentage composition. For example, in 1962, two chemists made a new compound from xenon and fluorine. Before 1962, scientists thought that xenon did not form compounds. The scientists analyzed their surprising find. They found that it had a percentage composition of 63.3% Xe and 36.7% F, which is the same as that for the formula XeF4. Percentage composition not only helps verify a substance s identity but also can be used to compare the ratio of masses contributed by the elements in two substances, as in Figure 8. 

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. 

The theoretical chemical formula of a mineral is unique and identifies only one species. Nevertheless, the actual chemical composition is usually variable within a limited range owing to the isomorphic substitutions (i.e., diadochy), or/and low presence of traces of impurities. The relative atomic or molecular mass (based on C = 12.000) of minerals is calculated from the theoretical formula using the last value of atomic masses adopted by the International Union of Pure and Applied Chemistry (lUPAC) in 2001, and the theoretical chemical composition is commonly expressed in percentage by weight (wt.%) of elements and sometimes oxides for oxygenated minerals. 

Where do chemical formulas come from They come from the same source as any fundamental chemical information, that is, from experiments, usually performed in the laboratory. Among other things, chemical analysis can give us the percentage composition of a compound. Such data give us the empirical formula of the compound. 

Formula mass, molar mass, and percentage composition can be calculated from the chemical formula for a compound. 

For a totally unknown compound (unknown chemical source or history) you will have to use this type of calculation to obtain the suspected empirical formula. However, if you have prepared the compound from a known precursor by a well-known reaction, you will have an idea of the structure of the compound. In this case, you will have calculated the expected percentage composition of your... 

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 ... 

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. 

Given only a molecular formula (perhaps derived from an experimentally determined percentage composition and a molecular weight determination) and some chemical evidence that suggests what functional groups might be present, how might we proceed to propose a possible structure ... 

Answer A is the fractional representation of the presence of each atom in the formula. Composition is based on mass percentage. Answer C is the chemical composition of Mg(N02)2, magnesium nitrite. Answer D is the chemical composition of "MgNCh", a formula that results from not balancing charges. 

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