Ionic compounds are composed of discrete cations and anions combined in ratios to yield electrically neutral bulk matter. The model shows the molecular structure of aspirin, C 9H 8O 4.ġ51.16 amu Formula Mass for Ionic Compounds The average mass of an aspirin molecule is 180.15 amu. Likewise, the molecular mass of an aspirin molecule, C 9H 8O 4, is the sum of the atomic masses of nine carbon atoms, eight hydrogen atoms, and four oxygen atoms, which amounts to 180.15 amu ( Figure 2). The model shows the molecular structure of chloroform. The average mass of a chloroform molecule, CHCl 3, is 119.37 amu, which is the sum of the average atomic masses of each of its constituent atoms. Figure 1 outlines the calculations used to derive the molecular mass of chloroform, which is 119.37 amu. The average molecular mass of a chloroform molecule is therefore equal to the sum of the average atomic masses of these atoms. The molecular formula of chloroform indicates that a single molecule contains one carbon atom, one hydrogen atom, and three chlorine atoms. Consider chloroform (CHCl 3), a covalent compound once used as a surgical anesthetic and now primarily used in the production of the “anti-stick” polymer, Teflon. Formula Mass for Covalent Substancesįor covalent substances, the formula represents the numbers and types of atoms composing a single molecule of the substance therefore, the formula mass may be correctly referred to as a molecular mass. These ideas can be extended to calculate the formula mass of a substance by summing the average atomic masses of all the atoms represented in the substance’s formula. In an earlier chapter, we described the development of the atomic mass unit, the concept of average atomic masses, and the use of chemical formulas to represent the elemental makeup of substances. Understanding the relationship between the masses of atoms and the chemical formulas of compounds allows us to quantitatively describe the composition of substances. For example, Dalton’s atomic theory was an attempt to explain the results of measurements that allowed him to calculate the relative masses of elements combined in various compounds. We can argue that modern chemical science began when scientists started exploring the quantitative as well as the qualitative aspects of chemistry. Define the amount unit mole and the related quantity Avogadro’s numberĮxplain the relation between mass, moles, and numbers of atoms or molecules, and perform calculations deriving these quantities from one another.Calculate formula masses for covalent and ionic compounds.Earlier, we found the molar mass of CO 2 to be 44.01 g/mol.īy the end of this section, you will be able to: Solution: We use dimensional analysis and the the molar mass of carbon dioxide to solve this problem. Problem: How many grams are in 0.762 mol of CO 2?
AL MOLAR MASS HOW TO
Likewise, now that we know how to determine molar masses for molecules, we can use this to solve problems, too. Solution: We use dimensional analysis and an equivalent term for Avogadro’s number to solve this problem. Problem: How many atoms are in 2.15 mol of solid sodium metal? Now that we’ve seen Avogadro’s number, we can use this value to solve problems. + 2 x (molar mass of O atoms) = 2 x (16.00 g/mol) = 32.00 g/molĤ4.01 g/mol Using Avogadro’s Number in Calculations How do we determine the molar masses of molecules? We do this by adding up the molar masses of all the atoms that comprise that molecule.Ģ x (molar mass of O atoms) = 2 x (16.00 g/mol) = 32.00 g/molġ x (molar mass of C atoms) = 1 x (12.01 g/mol) = 12.01 g/mol Molar masses of atoms are found directly on the periodic table.
We use the term molar mass to describe how many grams are in one mole of a substance.
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