chem chapter 3

chem chapter 3 - Chapter 3 Stoichiometry Average mass of...

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Chapter 3 Stoichiometry
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Average mass of the object Objects behave as though they were all identical. Example 1. A pile of marbles weigh 394.80 g. 10 marbles weigh 37.60 g. How many marbles are in the pile?
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Average atomic mass (amu) Elements occur in nature as mixtures of isotopes. Carbon (C) 12 C 98.89% 13 C 1.11% 14 C < 0.01% 98.89% of 12 amu + 1.11% of 13.0034 amu = (0.9889)(12 amu) + (0.0111)(13.0034 amu) = 12.01 amu exact number (standard) There is not a single atom with mass 12.01
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Average atomic mass (amu) There is not a single atom with mass 12.01 We can consider carbon to be composed of only one type of atom with a mass of 12.01. This enables us to count atoms of natural carbon by weighing a sample of carbon.
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Atomic mass Sodium has a mass of 22.99 amu on the periodic table Weighted average mass of different sodium Isotopes (13) 22 Na, 23 Na, 24 Na Na 22.99 11 Chlorine (Cl) as an example: mass 35.5 amu 35 Cl and 37 Cl 75% 35 Cl, and 25% 37 C 75*35 + .25*37 = 35.5
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Mass spectrometer
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Mass spectrometer Atoms or molecules are passed into a beam of electrons. Atoms or molecules loose electrons and become ions An external magnetic field is applied to the ions. The ions travel through the field and the path of their direction is bent according to their interaction with the external field. Heavier ions are deflected less that lighter ones. Where they hit the plate is indicative of their mass.
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Mass spectrometer
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Exercise Example 2. An element consists of 62.60% of an isotope with mass 186.956 amu and 37.40% of an isotope with mass 184.953 amu. Calculate the average atomic mass and identify the element .
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The Mole (mol) SI Unit and is used to measure the amount of substance •T h e mole is to the amount of substance as the gram is to mass. Used for counting atoms Defined: The number equal to the number of carbon atoms in exactly 12 grams of pure 12 C. 1 mole of something = 6.022 x 10 23
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The Mole A dozen represents 12 items (eggs or donuts) The mole represents a numerical value. A mole will always equal 6.02 X 10 23 atoms or molecules Atoms and molecules are very very small Represents: A specific number of particles (atoms, molecules) A definite and specified mass of a substance 1 mole C = 6.022 x 1023 C atoms = 12.01 g C The mass of 1 mol of an element = the atomic mass in grams
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The Mole 2 ( H 2 ) +1 ( O 2 ) 2 ( H 2 O ) The Mole: A unit representing a very big number 2 moles of H 2 molecules react with 1 mole of O 2 molecules to produce 2 moles of H 2 O molecules Each reaction has a fixed Mole Ratio that can be used for calculations
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Example 3. Calculate the number of iron atoms in a 4.48 mole sample of iron. 2.70×10
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chem chapter 3 - Chapter 3 Stoichiometry Average mass of...

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