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Unformatted text preview: so lving problems invo lving massmolenumber relat ionships of elements or compounds, we can use: · The molar mass to convert between mass and mo les.
· Avogadro’s number (6.02x10 23 ) to convert between mo les and number of entit ies. Examples: 1. How many moles o f iron are present in 25.0 g of iron? 25.0 g Fe ( 1 mole ) = 0.448 mol Fe 55.85 g 2. What is the mass of 5.00 mo le of water? 3. How many magnesium atoms are present in 5.00 g of Mg? 1 mol 6.02x10 23 atoms 5.00 g Mg( )( ) =1.24x1023 atoms Mg 24.3 g 1 mol 4. How many mo lecules o f HCl are present in 25.0 g of HCl? 17 Chemistry 51 Chapter 6 MOLES OF ELEMENTS IN A FORMULA
· The subscripts in a chemical formula of a compound indicate the number of atoms of each type of element. For example, in a mo lecule of aspirin, C9H8O4, there are 9 carbon atoms, 8 hydrogen atoms and 4 oxygen atoms.
· The subscript also indicates the number of mo les of each element in one mo le of the compound. For example, one mo le o f aspirin contains 9 mo les of carbon atoms, 8 mo les o f hydrogen atoms and 4 mo les of oxygen atoms. C9H8O4 Atoms in 1 molecule Carbon 9 atoms C Hydrogen 8 atoms H Oxygen 4 atoms O Moles of atoms in 1 mole 9 mo les C 8 mo les H 4 mo les O · Using the subscripts from the aspirin formula, one can write the fo llowing conversio n factors for each of the elements in 1 mole of aspirin: 9 moles C
1 mole C 9 H 8 O 4 8 moles H
1 mole C 9 H 8 O 4 4 moles O 1 mole C 9 H 8O 4 Examples: 1. Determine the mo les of C atoms in 1 mo le of each of the fo llowing substances: a) Acetaminophen used in Tyleno l, C8H9NO2 b) Zinc dietary supplement, Zn(C2H3O2)2 2. How many carbon atoms are present in 1.50 mo les of aspirin, C9H8O4? 18 Chemistry 51 Chapter 6 SUMMARY OF MASSMOLE CALCULATIONS Mass Mass of element Particles Moles Molar Mass Moles of element Avogadro’s No. Atoms or ions F o r m u l a Mass of compound Molar Mass Moles of compound 19 Avogadro’s No. Molecules or formula units of compound Chemistry 51 Chapter 6 STOICHIOMETRY
· Stoichiometry is the quant itative relat ionship between the reactants...
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