Ch_03a_0920

# Ch_03a_0920 - Chapter 3 Stoichiometry: Chemical...

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2 Chapter 3 Stoichiometry: Chemical Calculations 1. Calculations based on chemical formulas 2. The use of chemical equations 3. Calculations based on chemical equations 3 Example: water - H 2 O Molecular Mass Molecular mass is the sum of the masses of the atoms represented in a molecular formula. 2 Hydrogen atoms 2(1.0079 u) 1 Oxygen atom + 15.9994 u = 18.0152 u

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4 Molecular Mass Glucose - C 6 H 12 O 6 = 6( 12.0107 u ) + 12( 1.0079 u ) + 6( 15.9994 u ) = 180.1154 u Sulfur dioxide - SO 2 = 32.066 u + 2( 15.9994 u ) = 64.065 u 5 Formula Mass Formula mass is the sum of the masses of the atoms or ions present in a formula unit. Na + Cl - Na + Na + Cl - Cl - Cl - Na + Crystal of sodium chloride One Na + and one Cl make a formula unit for sodium chloride The mass of one formula unit is: = 22.9898 u + 35.4527 u = 58.4425 u
6 consider the formation of carbon dioxide At the molecular level . .. Problem: how does one determine # of carbon atoms? Note that the mass of C atom in grams is ~2.00 x 10 –23 g! 7 Avogadro’s Number, N A A mole (mol) is an amount of substance that contains as many elementary entities as there are atoms in exactly 12 g of the carbon-12 isotope. The number of elementary entities in one mole of anything N A = 6.02214199 x 10 23 entities mol –1 -or- 1 mole 6.022 x 10 23 entities 12 g of the carbon-12 isotope

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8 Examples of N A 1 mole of stars in the universe = 6.022 x 10 23 stars 1 mole of pennies = 6.022 x 10 23 pennies (beats the lottery!) 1 mole of tennis balls = 6.022 x 10 23 tennis balls
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## This note was uploaded on 05/06/2008 for the course CHEM 103 taught by Professor Forgot during the Spring '07 term at CUNY City.

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Ch_03a_0920 - Chapter 3 Stoichiometry: Chemical...

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