Chemical formula calculating percentage

We can turn this sort of calculation around and convert chemical formula into percentage composition. 

The elemental analysis of a compound is usually determined by a laboratory that specializes in this technique. A chemist who has prepared a new compound sends a sample to the laboratory for analysis. The laboratory charges a fee that depends on the type and number of elements analyzed. The results are returned to the chemist as a listing of mass percent composition. The chemist must then figure out which chemical formula matches this composition. If a chemist has reason to expect a particular chemical formula, the observed percentages can be matched against the calculated percentages for the expected formula. This process is illustrated in Example 3-13. 

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. 

Calculating Percentage Composition from a Chemical Formula... 

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. 

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. 

Chemical formulas can be used to calculate percentage composition. 

Calculations of volumetric analysis ordinarily consist of transforming the quantity of titrant used (in chemical units) to a chemically equivalent quantity of analyte (also in chemical units) through use of a stoichiometric factor. Use chemical formulas (NO CALCULATIONS REQUIRED) to express this ratio for calculation of the percentage of (a) hydrazine in rocket fuel by titration with standard iodine. Reaction ... 

Fig. 14-1 Standard 3 x 5 in. JCPDS diffraction data card (card 628 from Set 5) for sodium chloride. Appearing on the card are 1 (file number), 2 (three strongest lines), 3 (lowest-angle line), 4 (chemical formula and name of substance), 5 (data on diffraction method used), 6 (crystallographic data), 7 (optical and other data), 8 (data on specimen), and 9 (diffraction pattern). Intensities are expressed as percentages of Ii, the intensity of the strongest line on the pattern. Most cards have a symbol in the upper right comer indicating the quality of the data (high quality), i (lines indexed, intensities fairly reliable), c (calculated pattern), and o (low reliability). (Courtesy of Joint Conunittee on Powder Diffraction Standards.)...

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. 

Calculating the percentage composition of any element in a substance is straightforward if the chemical formula is known. The calculation depends on the formula weight of the substance, the atomic weight of the element of interest, and the number of atoms of that element in the chemical formula ... 

Analyze We are given a chemical formula and asked to calculate the percentage by mass of each element. 

Chemical formulas are expressed in terms of numbers of particles. In this problem, we have to start with masses and somehow infer information about the numbers of particles. We did a similar problem in this chapter the determination of an empirical formula from percentage by mass data. In this case, with the experiment described, we can determine the mass information for each element in the unknown compound—providing the same type of data we had from percentage mass calculations. Then, because we know the empirical formula and we know the molar mass of the oxygen, we can determine the molar mass of the unknown metal. 

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. 

Analyze Given tire chemical formula of a compound, C12H22O11, we are asked to calculate its percentage composition, meaning the percent by mass of its component elements (C, H, and O). 

The next section describes the calculation of mass percentages. Then, in two following sections, we describe how to determine a chemical formula. 

As you have seen, a chemical formula indicates the elements as well as the relative number of atoms or ions of each eiement present in a compound. Chemical formulas also allow chemists to calculate a number of characteristic values for a given compound. In this section, you will learn howto use chemical formulas to calculate the formula mass, the molar mass, and the percentage composition by mass of a compound. 

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

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 ... 

Alternatively, to protect confidential information, you may wish to enter only the percentage by which the weight of the chemical in the wastes has changed. This figure may be calculated using the following formula ... 

The chemical makeup of a substance is described by its percent composition—the percentage of the substance s mass due to each of its constituent elements. Elemental analysis is used to calculate a substance s empirical formula, which gives the smallest whole-number ratio of atoms of the elements in the compound. To determine the molecular formula, which may be a simple multiple of the empirical formula, it s also necessary to know the substance s molecular mass. Molecular masses are usually determined by mass spectrometry. 

The enantiomeric excess (e.e.) is a similar method for expressing the relative amounts of enantiomers in a mixture. To compute the enantiomeric excess of a mixture, we calculate the excess of the predominant enantiomer as a percentage of the entire mixture. For a chemically pure compound, the calculation of enantiomeric excess generally gives the same result as the calculation of optical purity, and we often use the two terms interchangeably. Algebraically, we use the following formula ... 

The determination of the empirical formula of a compound can be made experimentally, by determining the percentage amounts of elements present in the substance using the methods of quantitative chemical analysis. At the same time the relative molecular mass of the compound has to be measured as well. From these data the empirical formula can be determined by a simple calculation. If, for some reason, it is impossible to determine the relative molecular mass the simplest (assumed) formula only can be calculated from the results of chemical analysis the true formula might contain multiples of the atoms given in the assumed formula. 

I was characterized by powder X-ray diffraction (PXRD), energy dispersive analysis of X-rays (EDAX), chemical analysis, thermogravimetric analysis (TGA) and IR spectroscopy. EDAX analysis indicated the ratio of Mn S to be 3 2. The presence of fluorine was confirmed by analysis and the percentage of fluorine estimated by EDAX in a field emission scanning electron microscope was also satisfactory. Thermogravimetric analysis also confirms the stoichiometry of the compound. Bond valence sum calculations and the absence of electron density near fluorine in the difference Fourier map also provide evidence for the presence of fluorine. The sulfate content was found to be 30.8% compared to the expected 32% on the basis of the formula. 

In the MTT assay, after a 24 or 48 h incubation of the cultured cells, the culture medium was removed and 20 pi of the MTT solution prepared at 5 mg/ml (Sigma Chemical Company, MO, USA) was added to each well for 4 h. The resulting crystals were dissolved in dimethyl sulfoxide (DMSO). The controls included native cells and the medium itself. The spectrophotometric absorbance of each well was measured with the use of a microplate reader (ELx 800, Bio-Tek Instruments, Winooski, VT, USA) at 550 mn. The cytotoxicity percentage was calculated by the formula percent cytotoxicity (cell death) = (1 - [absorbance of experimental wells/ absorbance of control wells]) x 100%. 

There are several types of calculations that can be undertaken once we recognize the concept that a mole is simply a way to count particles. We can determine the empirical formula of a chemical based on the mass percentage analysis of its elements. We can also determine the molar concentration of solutions prepared by dissolving a known mass of the solute or by diluting a concentrated solution. 

---