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# CHAPTER 9: THE MOLE CONCEPT

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CHAPTER 9 THE MOLE CONCEPT Problems 1 20 23 26 29 46 77 78 9 1 AVOGADRO S NUMBER The mole is a collective quantity Examples of collective quantities 1 dozen 12 1 pair 2 1 mole 6 02 x 1023 particles particles atoms ions molecules etc How big is this The volume of 6 02 1023 softballs is about equal to the volume of the Earth This extremely huge is known as Avogadro s number The mole has also been defined as the of C atoms in exactly 12 grams of Carbon 12 9 2 MOLE CALCULATIONS I Avogadro s number is a useful conversion factor E g 6 02 x10 23 atoms 6 02 x10 23 molecules or 1 mole 1 mole Example How many atoms are in 10 0 moles of Pb Example How many moles of C atoms are present in a sample of 1 25 1024 C atoms 9 3 MOLAR MASS Recall atomic mass is average mass for one atom of an element units amu For problems involving masses find the mass of the element on the periodic table E g atomic mass of Cl 35 45 amu Molar Mass mass in grams of 1 mole of substance units g mol Numerically same as atomic mass but units are different Comparison of masses 1 Carbon atom weighs 12 01 amu 1 mole of Carbon atoms weighs 12 01 g molar mass of C 12 01 g mol CHM 130 Chapter 9 1 H2O molecule weighs 18 02 amu 1 mole of H2O molecules weighs 18 02 g molar mass of H2O 18 02 g mol page 1 of 4 Example Calculate the molar mass for the following elements or compounds A O2 2 molar mass of O 2 16 00 g mol 32 00 g mol B NaCl C CO2 D K2SO4 E NH4 3PO4 9 4 MOLE CALCULATIONS II Molar Mass is also a useful conversion factor between grams to moles Use the unit analysis method write molar mass as a fraction make sure that the units cancel and give you the units that you are solving for Example What is the mass in grams of 0 0235 moles of Na Example What is the mass in grams of 3 75 moles of FeCl3 Example How many moles are in 12 6 grams of H2O 9 5 MOLAR VOLUME Avogadro s Law An equal number of gas molecules at the same temperature and pressure will occupy the same volume Molar volume is the volume occupied by 1

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