I. Moles• 1 mole is 6.02 x 1023 of anything!!
• 6.02 x 1023 is called Avogadro's number.
• A mole can be 6.02 x 1023 atoms or molecules
A Mole is a UnitSing-a-long!!!
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A. Empirical Formula
• Simplest ratio of atoms in a compound (Ex. C2H5)
• The subscript tells you how many moles of each ion in the compound.
• Ex. Al2O3 = 2 mol Al+3 3 mol O-2
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B. Molecular Formula• Actual ratios of atoms in a molecule or
compound (Ex. C4H10)
• Molecular formulas are whole-number multiples of an empirical formula
• Ex: C4H10 molecular formula
C2H5 empirical formula
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III. Stoichiometry
• The study of quantitative relationships that can be derived from chemical formulas and equations
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• 1 mole of atoms has a mass equal to the atom’s atomic mass in grams.
• Atomic mass located on periodic table.
• Round to the nearest TENTH ( 0.1)
Example:
C= 12.0 amu = 12.0 g/mol
O= 16.0 amu = 16.0 g/mol
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B. Gram Formula Mass (GFM)
• the sum of all the atomic masses in the formula of the substance
1. add up the mass of each atom in the formula.
2. Multiply by the number of each atom if there is more than one of each atom.
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Element Atomic Mass # of Atoms in
Formula
Product
H 1 2 2
O 16 1 16
Total Mass = 18 g
Example: silver nitrate
Element # of atoms Mass Product
Ag = 1 × 108amu = 108 g
N = 1 × 14amu = 14 g
O = 3 × 16 amu = 48 g
170g/mol
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Regents Practice
The gram formula mass of NH4Cl is
(1) 22.4 g/mole
(2) 28.0 g/mole
(3) 53.5 g/mole
(4) 95.5 g/mole
N 1 x 14.0 =
H 4 x 1.0 =
Cl 1 x 35.5 = _______
g/mole
1. Calculating Moles from Mass
Formula on table T in reference table
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given mass (g)
Gram formula mass
Mole =
2. Calculating Grams from Moles
• Rearrange the formula in
table T to solve for grams
given mass (g)
Gram formula mass
Mole =
Mole x GFMGrams =
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• Step1: Find the formula mass of the substance and express it in grams per mole
• Step 2: Apply the formula
mol =grams_
GFM
mol =390g__
110 g/mol
= 3.5 mol
CaCl2Ca = 40 × 1 = 40Cl = 35 × 2 = 70
110 g/mol