Wake-up
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Wake-up
1. Determine the empirical formula for the following: 28.4% Copper and 71.6% Bromine
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Molecular Formula
What are Molecular Formulas?How to calculate molecular formulas?
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Empirical FormulaA chemical formula that shows the lowest whole
number ratio of all atoms in a compound
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Molecular FormulaA chemical formula that shows the total number
and kinds of atoms in a molecule
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Recall from yesterday
Compound A is Empirical Formula
Compound B is Molecular Formula
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How to find Molecular Formulas?1. Write down what you know.
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of
butane?
Empirical formula = C2H5
Molar Mass = 60g/mol
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How to find Molecular Formulas?2. Calculate/Find the Empirical Formula
(if needed)
C2H5
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of
butane?
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How to find Molecular Formulas?3. Calculate the empirical formula mass (efm)
using the empirical formula
C = 2 x 12.01 = 24.02H = 5 x 1.00 = 5
Empirical Formula Mass = 24.02 + 5
29.02
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How to find Molecular Formulas?4. Divide the molar mass (that is provided in the
problem) by the empirical formula mass
The simplest formula for butane is C2H5 and its molecular mass is 60g/mol. What is the molecular formula of
butane?
60g/mol29.02g = 2 mole
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How to find Molecular Formulas?5. Multiply the empirical formula subscripts by
the whole number you found in step 4 to get the molecular formula.
C2H5 x 2 = C4H10
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Example #1The simplest formula for vitamin C is C3H4O3.
Experimental data indicates that the molecular mass of vitamin C is about 180 g/mol. What is
the molecular formula of vitamin C?
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Example #2A compound contains 18.8% sodium, 29%
chlorine, and 52.2% oxygen, by mass. If the molar mass of the compound in 122.44 g/mol,
determine the empirical and molecular formulas.
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Example #3Caffeine has an elemental analysis of 49.48%
carbon, 5.190% hydrogen, 16.47% oxygen, and 28.85% nitrogen. It has a molar mass of 194.19
g/mol. What is the molecular formula of caffeine?
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Molecular Formula
What are Molecular Formulas?How to calculate molecular formulas?