Chy102-Tutorial 03

Chy102-Tutorial 03 - General Chemistry General Chem. 102...

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1 General Chemistry Chem. 102 for Engineering General Chemistry General Chemistry Tutorial 3
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2 Objectives ¾ Define atomic masses ¾ Atomic masses and isotopic abundance ¾ Define the mole ¾ Calculate the number of moles ¾ Calculate the molar mass of any compound ¾ Determine the percent composition of compounds ¾ Determine the formula of compounds ¾ Balance chemical equations ¾ Stoichiometry in chemical reaction ¾ Calculations involving a limiting reactants ¾ Calculation of percent yield of a product
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3 Example 1 Assume that magnesium consists of three isotopes having the abundances and masses given in table to the left. According to these data, calculate the average atomic mass of magnesium. 25.983 amu 11.17% 26 Mg 24.986 amu 10.13% 25 Mg 23.985 amu 78.70% 24 Mg Mass Abundance Isotope a) 25.00 amu b) 2.431 amu c) 2431 amu d) 24.31 amu e) None of the above. 31 . 24 90 . 2 53 . 2 88 . 18 100 983 . 25 17 . 11 100 986 . 24 13 . 10 100 985 . 23 70 . 78 ) Mg ( mass Atomic = + + = × + × + × = Solution 100 ) (y mass atomic )% ( ....... 100 ) (y mass atomic )% ( 100 ) (y mass atomic )% ( ) ( n 2 2 1 1 × + + × + × = n y y y y mass Atomic Generally: Generally: 1 amu = 1/12 of mass of 12C isotope = 1.66054 • 10 -24 g
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4 Example 2 The two isotopes of potassium with significant abundance in nature are 39 K (isotopic mass 38.96 amu, 93.27%) and 41 K (isotopic mass 40.96 amu, 6.73%). Fluorine has only one naturally occurring isotope, 19 F (isotopic mass 18.99 amu). Calculate the molar mass of potassium fluoride. Average atomic mass of K = 38.96 x (93.27/100) + 40.96 x (6.73/100) = 39.09 Since fluorine has only one isotope, atomic mass of F = 18.99 Molar mass of KF = 39.09 + 18.99 = 58.08 Solution:
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5 Example 3 Silver (atomic weight 107.868) has two naturally-occurring isotopes with isotopic
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This note was uploaded on 12/13/2010 for the course CHEM 102 taught by Professor Raafat during the Spring '10 term at Ain Shams University.

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Chy102-Tutorial 03 - General Chemistry General Chem. 102...

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