Empirical formula of a compound

Any of these ratios, or their inverses, may he used as a conversion factor from the mass of one species to the mass of the other. For instance, to find the mass of CaF2 that contains 3.55 g Ca from these numbers, we calculate 

Calculate the number of grams of fluorine in a sample of calcium fluoride that contains 2.01 g of calcium. 

Plan the solution. Then write the calculation setup and find the answer. 

11 Distinguish between an empirical formula and a molecular formula. 

Co to http //now.brookscole.com/ cracolice5e and dick Coached Problems for a simulation on Compounds and Moles. 

PURPOSE OF EXPERIMENT Determine the empirical formula of lead iodide. 

The empirical formula of a compound tells us the types of atoms present in a compound as well as the ratio of different types of atoms. The empirical formula does not tell us the actual number of atoms in the molecule. For example, the empirical formula, BCI2/ represents a compound that has two atoms of chlorine for every boron atom. The subscripts of 1 (unwritten) and 2 are the smallest whole numbers that can be used to express the atomic ratio. The molecular formula indicates the actual number of atoms of each element in one molecule. The molecular formula, B2CI4, tells us that one molecule contains two boron atoms and four chlorine atoms. The simplest ratio of atoms in this B2CI4 molecule is BCI2, the empirical formula. 

An ionic compound is an aggregrate of ions, these being present in a definite ionic ratio that is characteristic of the compound. Since there are no discrete molecules in the infinite lattice of an ionic substance, only an empirical formula can be used to express its composition. Thus, for nickel(II) chloride, which is composed of a collection of Ni t and Cl ions in the ratio of one to two, the empirical formula is NiCl2. There is no molecular formula for nickel(II) chloride. 

In this experiment you will determine the empirical formula of a compound composed of lead and iodine. A weighed quantity of lead is reacted with nitric acid, HNO3, solution. The resulting lead nitrate solution is then reacted with sodium iodide, Nal, solution to form insoluble lead iodide, which is filtered, dried, and weighed. From your experimental data you can calculate the percentage composition and the ratio of moles of lead to moles of iodine in the compound, and then write the empirical formula. 

and Purcell, K. F., Chemistry and Chemical Reactivity, Saunders College Publishing, Philadelphia, 1987, sections 2.5 and 2.11a. 

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To determine the empirical formula of a compound, we begin by measuring the mass of each element present in a sample. The result is usually reported as the mass... 

The empirical formula of a compound is determined from the mass percentage composition and the molar masses of the elements present. 

This flowchart summarizes the method for using combustion analysis to determine the empirical formula of a compound that contains no elements other than C, H, and O. 

EXAMPLE 4.12. What is the empirical formula of a compound which contains 40.0% sulfur and 60.0% oxygen, by mass ... 

Calculate the empirical formula of a compound with a percent composition of 88.9% oxygen and 11.1% hydrogen. 

In addition to using the absolute intensities of the atomic emission lines, the peak intensity ratios of these lines have been used to analyze samples. Tran et al. [77] analyzed the atomic intensity ratios of several organic compounds with the hope to determine the empirical formula of a compound based on the ratios from several elements. Calibration curves were built based on C H, C 0, and C N atomic emission ratios from various compounds that covered a wide range of stoichiometries. Then, four compounds with known stoichiometries were tested against the calibration curves. The ratios determined from the calibration curves were compared with the actual stoichiometries and showed accuracy of 3% on average. In the study of nitroaromatic and polycyclic aromatic hydrocarbon samples, the ratios between C2 and CN and between O and N of different samples were shown to correlate with the molecular formula [75], Anzano et al. [71] also attribute success of their correlation of plastics to differences in the C/H atomic emission intensity ratio of each sample. 

The empirical formula of a compound can be determined in a laboratory experiment by finding the ratio between the number of moles of the elements in the compound. The number of moles of each element can be calculated from the experimental values of the weights in which the elements combine by dividing by their corresponding atomic weights. If the molecular weight and the empirical formula of the compound are known, then the molecular formula of the compound can be determined. 

It is possible for different compounds to have the same empirical formula, as you can see in Figure 6.6. For example, benzene and acetylene both have the empirical formula CH. Each, however, is a unique compound. Benzene, C6H6, is a clear liquid with a molar mass of 78 g/mol and a boiling point of 80°C. Acetylene, C2H2, has a molar mass of 26 g/mol. It is a highly flammable gas, commonly used in a welder s torch. There is, in fact, no existing compound with the molecular formula CH. The empirical formula of a compound shows the lowest whole number ratio of the atoms in the compound. It does not express the composition of a molecule. 

In section 6.2, you learned how to calculate the empirical formula of a compound based on percentage composition data obtained by experiment. In section 6.3, you will learn how chemists use the empirical formula of a compound and its molar mass to determine the molecular formula of a compound. 

The carbon-hydrogen combustion analyzer can also be used to find the empirical formula of a compound that contains carbon, hydrogen, and one other element, such as oxygen. The difference between the mass of the sample and the mass of the hydrogen and carbon produced is the mass of the third element. 

Predict the empirical formula of a compound using the periodic table, and test your prediction through experimentation. 

Use the molar mass and empirical formula of a compound to determine the molecular (actual) formula of the compound. 

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