Compounds determining formula

Interconvert masses, moles,and formulas Determine percent compositions in compounds Determine formulas from composition data Recognize models from calculated molecular formulas Perform calculations on the purity of substances... 

A major task of chemical analysis is to determine the formulas of compounds. The formula found by the approach described here is the simplest formula, which gives the simplest whole-number ratio of the atoms present. For an ionic compound, the simplest formula is ordinarily the only one that can be written (e.g., CaCl2, Cr203). For a molecular compound, the molecular formula is a whole-number multiple of the simplest formula, where that number may be 1,2. 

If the sample consists of atoms of one element, the mass spectrum gives the isotopic distribution of the sample. The relative molar masses of the isotopes can be determined by comparison with atoms of carbon-12. If the sample is a compound, the formula and structure of the compound can be determined by studying the fragments. For example, the + 1 ions that CH4 could produce are CH4, CH3+, CH, CFI4, C+, and H4. Some of the particles that strike the detector are those that result when the molecule simply loses an electron (for example, to produce Cl I4+ from methane) ... 

The crystal structures of four chlorinated derivatives of di-benzo-p-dioxin have been determined by x-ray diffraction from diffractometer data (MoKa radiation). The compounds, their formulae, cell dimensions, space groups, the number of molecules per unit cell, the crystallographic B.-factors, and the number of observed reflections are given. The dioxin crystal structures were performed to provide absolute standards for assignment of isomeric structures and have been of considerable practical use in combination with x-ray powder diffraction analysis. 

Work out the molecular formula of the compound determined in Question 7(c) above, given that its molar mass is 58 gmol-1. (2)... 

The reaction of diphosphines, R2PPR2 (R = Me, Ph), with S4N4 in benzene at reflux produces intensely purple compounds of formula R2PS2N3 ( ,ax 550 nm) The diphenyl derivative is an air and thermally stable crystalline solid whereas the dimethyl compound forms very volatile, low melting crystals which undergo slow decomposition at room temperature. An X-ray structure determination showed it (R = Pr) to consist of a 6-membered ring in which the phosphorus atom lies 28 pm out of the plane... 

Loschmidt is remembered as a physicist for his determination of the Loschmidt number 61), the number of molecules in 1 mL of gas, but in 1861 he published a small booklet 62) in which he drew stmctural formulas for a large number of organic compounds. Two formulas of the Loschmidt type are reproduced in Figure 9. It is interesting to note that, in many ways, Loschmidt s formulae reflect Dalton s elemental symbols, and may, in fact, be based on Dalton s symbolism. 

The exact mass of a compound determined by high-resolution mass spectrometry is 212.0833. What is the molecular formula of the compound ... 

Compounds of formula [M BgLj], where B is a bridging anionic donor and L a neutral one, may be considered as formally derived from M3X8 adducts by solvolysis. The reduction of Nbv in acid solutions has been used for its qualitative and quantitative determination, but the exact nature of the reduced species remains unknown. The red-brown salt obtained as early as 1912 by reduction of Nbv in aqueous H2S04 has been formulated as [K4(H502)][Nb302(S04)6(H20)3] 5H20 (48) on the basis of a recent X-ray structure... 

In 1-octene solution, the following products are observed (21) a mixture of cis and trans 2-octene, a hydrocarbon of the formula C16H34, 2-octyl cyclohexanone, a compound of the formula C22H42O believed to be formed by the addition of 2 molecules of 1-octene to 1 molecule of the ketone, and a compound of formula C3oH6S0 believed to be formed by the addition of 3 molecules of 1-octene to 1 molecule of cyclohexanone. In addition, a considerable amount of a polymer is also formed. The complex mixture of products clearly indicates the difficulties in the study of photolysis in the condensed phase, particularly if it is necessary to determine the mechanism of the formation of the various products. 

MCrX3 (M = Li—Cs X = halide) have been reviewed770 and mass spectrometric studies of the compositions of MCrCl3 (M = K or Cs) vapours have been reported and the thermodynamic characteristics for the evaporation of these compounds determined.776 Electrode potential data for Cr11 in KCl-LiCl melts have been reported.78 CsCrI3 has been obtained by melting Csl and Crl2 (1 1) in a sealed, evacuated quartz tube. The lattice parameters of this compound have been determined and compared with those of other compounds of this formula type.79... 

The relation between the present value, P, of a sum of money, and its future value, F, is determined by the standard compound interest formula ... 

What products would be expected from the reaction of the compound the formula of which is shown below with lithium [dimethyl(phenyl)silyl]-iodidocuprate(I) Determine their configuration. 

The proton and 13C NMR spectra of a compound of formula C/tH N are shown here. Determine the structure of this amine, and give peak assignments for all of the protons in the structure. 

Then they use this information to determine the molecular formula of the compound. Determining the molecular formula is an important step in understanding the properties of the compound and developing a way to synthesize it in a laboratory. 

Molecular formulas give all the information that empirical formulas do, plus the ratio of the number of moles of each element to the number of moles of the compound. (Molecular formulas are used only for molecular substances, not ionic substances.) A molecular formula can be determined from the empirical formula of the compound and its formula mass First, divide the formula mass by the mass in amu of one empirical formula unit, which will result in a small integer. Then, multiply each subscript of the empirical formula by that integer. (Section 7.5)... 

The formula of a compound gives the relative number of atoms of the different elements present. It also gives the relative number of moles of the different elements present. As was shown in Sec. 7.5, the percent by mass of each element in a compound may be computed from its formula. Conversely, if the formula is not known, it may be deduced from the experimentally determined composition. This procedure is possible because once the relative masses of the elements are found, the relative numbers of moles of each may be determined. Formulas derived in this manner are called empirical formulas or simplest formulas. In solving a problem in which percent composition is given, any size sample may be considered, since the percentage of each element does not depend on the size of the sample. The most convenient size to consider is 100 g, for with that size sample, the percentage of each element is equal to the same number of grams. 

Formulas describe the composition of compounds. Empirical formulas give the mole ratio of the various elements. However, sometimes different compounds have the same ratio of moles of atoms of the same elements. For example, acetylene, C2H2, and benzene, CeHe, each have 1 1 ratios of moles of carbon atoms to moles of hydrogen atoms. That is, each has an empirical formula CH. Such compounds have the same percent compositions. However, they do not have the same number of atoms in each molecule. The molecular formula is a formula that gives all the information that the empirical formula gives (the mole ratios of the various elements) plus the information of how many atoms are in each molecule. In order to deduce molecular formulas from experimental data, the percent composition and the molar mass are usually determined. The molar mass may be determined experimentally in several ways, one of which will be described in Chap. 12. 

From the description given, the reactant is solid ammonium dichromate, (NH4)2Cr207(s), and the products are nitrogen gas, N2(g), water vapor, H20(g), and solid chromium(III) oxide, Cr203(s). The formula for chromium(III) oxide can be determined by recognizing that the Roman numeral III means that Cr3+ ions are present. For a neutral compound the formula must then be Cr203, since each oxide ion is O2-. 

A 1.42-g sample of a pure compound, with formula M2S04, was dissolved in water and treated with an excess of aqueous calcium chloride, resulting in the precipitation of all the sulfate ions as calcium sulfate. The precipitate was collected, dried, and found to weigh 1.36 g. Determine the atomic mass of M and identify M. 

A compound of the formula C2H6O2 corresponds to a molecular weight 62. Therefore the molecular formula of the compound determined is C2H6O2. 

Given the percentages by mass of the elements in a compound, determine its empirical formula and vice versa (Section 2.3, Problems 13-24). 

Determine formulas for the ions and compounds that form when electrons are gained or lost. 

Bupropion is present in a medication that is an antidepressant and is also used to aid in quitting smoking. The composition of bupropion is 65.13% carbon, 7.57% hydrogen, 14.79% chlorine, 5.84% nitrogen, and 6.67% oxygen. The simplest formula is the same as the molecular formula of this compound. Determine the formula. 

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