Molecular substances empirical formulas

Two substances have the same molecular and empirical formulas. Does this mean that they must be the same compound ... 

Not all polymers are formed by simply linking identical monomers together. Polyurethane, for example, can be formed by reacting the two compounds shown below with one another. Write molecular and empirical formulas for each of these two substances. 

Substance Empirical formula Molecular formula Substance Empirical formula Molecular formula... 

Write the molecular and empirical formulas of the following (a) the reactive substance dtborane, which has two boron atoms and six hydrogen atoms (b) the sugar called glucose, which has six carbon atoms, twelve hydrogen atoms, and six oxygen atoms. 

Explosive substance Empirical formula Proportion by mass (g) Molecular weight (g) Molar proportion in Ig of mixture Mol of atoms in Ig of explosive mixture ... 

Attempts to characterize polymeric substances had been made, of course, and high molecular weights were indicated, even if they were not too accurate. Early workers tended to be more suspicious of the interpretation of the colliga-tive properties of polymeric solutions than to accept the possibility of high molecular weight compounds. Faraday had already arrived at Cs Hg as the empirical formula of rubber in 1826, and isoprene was identified as the product... 

Suppose that 10.0 g of an organic compound used as a component of mothballs is dissolved in 80.0 g of benzene. The freezing point of the solution is 1.20°C. (a) What is an approximate molar mass of the organic compound (b) An elemental analysis of that substance indicated that the empirical formula is C3H2C1. What is its molecular formula (c) Using the atomic molar masses from the periodic table, calculate a more accurate molar mass of the compound. 

In a balanced chemical equation (commonly called a chemical equation ), the same number of atoms of each element appears on both sides of the equation, chemical equilibrium A dynamic equilibrium between reactants and products in a chemical reaction, chemical formula A collection of chemical symbols and subscripts that shows the composition of a substance. See also condensed structural formula empirical formula,- molecular formula structural formula. 

Effect of other factors on cellulose. Dry distillation at a temperature above 150°C causes cellulose to produce compounds of low molecular weight, such as water, methane, ethylene, carbon monoxide, carbon dioxide, acetic acid, and acetone. According to Pictet [49] dry distillation under reduced pressure yields a substance having the empirical formula C6H10Oj, laevo-glucosan which probably is /3-D-glucopyranose anhydride ... 

We recall from Chapter 10 that the percentages of the elements in a compound can be used to compute the simplest formula for the compound. When the substance is soluble in some suitable liquid, we can combine the empirical formula with a molecular-weight determination by freezing-point depression to get the true formula. 

The molecular weight of the compound can be obtained from the molecular formula by summing the products obtained by multiplication of the atomic weights of Ihe elements limes their subscripts in the molecular formula. The latter contains all the information that the empirical formula contains bill in addition specifies the number of atoms in the molecule and also the molecular weight of the substance. 

Self-Test F.5B The molar mass of oxalic acid, a toxic substance found in rhubarb leaves, is 90.0 g-mol, and its empirical formula is CH02. What is its molecular formula ... 

A formula such as C4H9, which is determined from data about percent composition, is called an empirical formula because it tells only the ratios of atoms in a compound. The molecular formula, which tells the actual numbers of atoms in a molecule, can be either the same as the empirical formula or a multiple of it, such as C8H18. To determine the molecular formula, it s necessary to know the molecular mass of the substance. In the present instance, the molecular mass of our compound (a substance called octane) is 114.2 amu, which is a simple multiple of the empirical molecular mass for C4H9 (57.1 amu). 

Just as we can derive the empirical formula of a substance from its percent composition, we can also calculate the percent composition of a substance from its empirical (or molecular) formula. The strategies for the two kinds of calculations are exactly opposite. Aspirin, for example, has the molecular formula C9H8O4 and thus has a CH 0 mole ratio of 9 8 4. We can convert this mole ratio into a mass ratio, and thus into percent composition, by carrying out mole-to-gram conversions. 

Elemental analysis can provide only an empirical formula. To determine the molecular formula, it is also necessary to know the substance s molecular mass. In the present problem, the molecular mass of naphthalene is 128.2 amu, or twice the empirical formula mass of C5H4 (64.1 amu). Thus, the molecular formula of naphthalene is C(2x5)H(2x4)/ or Ci0H8. 

Caproic acid, the substance responsible for the aroma of dirty gym socks and running shoes, contains carbon, hydrogen, and oxygen. On combustion analysis, a 0.450 g sample of caproic acid gives 0.418 g of H20 and 1.023 g of C02. What is the empirical formula of caproic acid If the molecular mass of caproic acid is 116.2 amu, what is the molecular 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 polymerisation of the linear BeH2 molecule is exactly analogous to the dimerisation of BH3. The Be-H-Be bridge is found in a number of molecular substances, e.g. in complexes having the empirical formula BeHRL, where L is a neutral ligand and R is an alkyl group ... 

The empirical formula is the formula for a compound that is expressed in the lowest ratio that can be calculated (refer to Chapter 2). Often, a substance must be analyzed to gather information leading to its identity. Various processes can be used to determine the composition of a sample, and an effective way of expressing these data is in the form of weight. Weights can be converted to moles and expressing a formula is the next logical step. The empirical formula is not necessarily the actual molecular formula however, the empirical formula does contain important information. 

The empirical formula CH2 is not a stable substance. It is necessary to determine the molar mass to determine the molecular formula. If this hydrocarbon were a gas or an easily volatilized liquid, its molar mass could be determined from the density of the gas, as shown in Chapter 5. Supposing such a determination yields a molar mass of about 55 g/mol, what is the molecular formula ... 

The formula weight for this compound is 88.1 g. Because this is exactly one half of the molecular weight, the subscripts for all substances in the empirical formula must be multiplied by 2 ... 

The correct answer is (A). The first step is to determine the number of moles of each substance present. From this we can determine the empirical formula, and later the molecular formula. When given percentages, you can assume a 100 g sample, which allows you to directly convert each percentage directly to an amount in grams. The number of moles of each substance can be calculated as shown below ... 

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. 

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. 

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)... 

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