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# CHEM 1320 Study Guide - Unified Atomic Mass Unit, Bromine, Dihydrogen Cation

13 pages40 viewsFall 2013

Department
Chemistry
Course Code
CHEM 1320
Professor
Ganley

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Chapter 3: Stoichiometry of Formulas and Equations
Mass Relationships in Chemical Reactions
8/28
Microscopic: atoms and molecules
Macroscopic: grams
Atomic mass: mass of an atom in amu
Carbon=12.01amu
Hydrogen=1.008amu
Oxygen=16amu
Average atomic mass: on other page
Mole (mol): Contains as many particles as there are atoms in 12
grams of 12C
1mol=NA=6.022x10^23
How big is a mole?
Large burger chain:
How long to serve a mole of hamburgers?
6.022x10^23 hamburgers
----------------------------------- = 1.67x10^14
3.6x10^9 hamburgers/day
=458 billion
years!
Counting objects of fixed relative mass:
12 apples @ 7g each=84g
12 oranges @4g each=48g
55.85gFe=6.022x10^23 atoms of Fe
32.07gS=6.022x10^23 atoms of S
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1 12C atom 12.00amu 1.66x10^-24g
--------------- x ------------------------------ = -----------------------
12.00amu 6.022x10^23 12C atoms 1amu
1amu=1.66x10^-24 or 1 g=6.022x10^23amu
conversion table=molar mass in g/mol
Molecular mass (or molecular weight) is the sum of the atomic
masses (in amu) in a molecule
SO2:
1S=32.07amu
1O=16.00amux2
------------------------
SO2=64.07amu
For any molecule: molecular mass (amu)=Molar mass (grams)
Table 3.1
How many atoms are in 0.551 g of K?
1mol K=39.10g K
1mol K=6.022x10^23 atoms K
0.551 g K 1 mol K 6.022x10^23 atoms K
x --------------- x ------------------------------- =
39.10 g K 1 mol K
=8.49x10^21 atoms K
How many H atoms are in 72.5 g of C3H8O?
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1 mol C3H8O=(3x12) + (8x1) +16=60 g C3H8O
1 mol C3H8O molecules=8 mol H atoms
1 mol H=6.002x10^23 atoms H
72.5C3H8O 1mol C3H8O 8 mol H atoms 6.022x10^23 Hatoms
x -------------- x --------------- x
------------------------ =
60g C3H8O 1mol C3H8O 1mol H atoms
5.82x10^24H atoms
8/30
Formula mass is the sum of the atomic masses (in amu) in a
formula unit of an ionic compound.
1Na=22.99amu
+
1Cl=35.45amu
=
Nacl=55.44amu
For any ionic compound, formula mass (amu)=molar mass (grams)
1 formula unit NaCl=58.44 amu
1 mole NaCl=58.44 g mol
Formula mass of Ca3(PO4)2 ?
3Ca=3x40.08amu
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