notes_Chapter 3 - hapter #3 : Stoichiometry - ole - Mass...

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Unformatted text preview: hapter #3 : Stoichiometry - ole - Mass Relationships in Chemical Systems 1. Atomic Masses 2. The Mole 3. Determining the Formula of an Unknown Compound 4. Writing and Balancing Chemical Equations 5. Calculating the amounts of Reactant and Product 6. Limiting Reagent Calculations: Atomic Mass Atomic Definitions Atomic Mass Unit (AMU) 1/12 the mass of a carbon - 12 atom on this scale Hydrogen has a mass of 1.008 AMU. Dalton (D) = The new name for the Atomic Mass Unit. One Dalton = one Atomic Mass Unit on this scale, 12 C has a mass of 12.00 Daltons. Isotopic Mass = The relative mass of an Isotope relative to the 12 C isotope standard = 12.00 amu. Atomic Mass or “Atomic Weight” of an element = the average of the masses of its naturally occurring isotopes weighted according to their abundances. Calculating Atomic Mass The Mass Spectrometer Operation of a Mass Spectrometer A. Sample Vaporized (Made into a gas). B. Electron guns removes an electron forming a positively charged species. C. Positive ion accelerated through an electric field. D. Magnetic deflection. • Lighter ions deflected more than heavier ones. E. Impact on detector 3.1) Operation of a Mass Spectrometer A B C D E Calculating the “Average” Atomic Mass of an Element 24 Mg (78.7%) 23.98504 amu 25 Mg (10.2%) 24.98584 amu 26 Mg (11.1%) 25.98636 amu Total = With Significant Digits = amu Problem: Calculate the average atomic mass of Magnesium! Magnesium has three stable isotopes, 24 Mg ( 78.7%); 25 Mg (10.2%); 26 Mg (11.1%). Calculating the “Average” Atomic Mass of an Element 24 Mg (78.7%) 23.98504 amu x 0.787 = 18.876226 amu 25 Mg (10.2%) 24.98584 amu x 0.102 = 2.548556 amu 26 Mg (11.1%) 25.98636 amu x 0.111 = 2.884486 amu 24.309268 amu Problem: Calculate the average atomic mass of Magnesium! Magnesium Has three stable isotopes, 24 Mg ( 78.7%); 25 Mg (10.2%); 26 Mg (11.1%). With Significant Digits = 24.3 amu CLASS PROBLEM Isotopes of Hydrogen Natural Abundance • 1 1 H 1 Proton 0 Neutrons 99.985 % 1.00782503 amu • 2 1 H ( D ) 1 Proton 1 Neutron 0.015 % 2.01410178 amu • 3 1 H (T) 1 Proton 2 Neutrons -------- ---------- The average mass of Hydrogen is 1.008 amu Element #8 : Oxygen, Isotopes • 16 8 O 8 Protons 8 Neutrons 99.759% 15.99491462 amu • 17 8 O 8 Protons 9 Neutrons 0.037% 16.9997341 amu • 18 8 O 8 Protons 10 Neutrons 0.204 % 17.999160 amu H 2 18 O WATER $700 / mL The Mole Not A Mole MOLE – just a number, like a dozen • The Mole is based upon the definition: The amount of substance that contains as many elementary particles as there are atoms in exactly 12 grams of carbon -12 (i.e., 12 C). 1 Mole = 6.022045 x 10 23 particles (atoms, molecules, ions, electrons, apples, hairs, etc…) = N A particles ~100 million x 100 million x 100 million Avogadro’s Number ( N A ) N A = 6.022045 x 10 23 = # of particles (atoms, molecules, ions, electrons, or…) in one mole of that thing....
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This note was uploaded on 02/06/2010 for the course CHEM 142 taught by Professor Iandearing during the Spring '10 term at University of Warsaw.

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notes_Chapter 3 - hapter #3 : Stoichiometry - ole - Mass...

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