Calculations based on Compounds
Objective: To calculate formulas of compounds from data
Samples are analyzed to determine type & amount of each
component (type of atoms)
Chapter 11, pp. 322 - 324
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Molar mass
Practice mole conversions
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Check answers from methane problems
Determining formulas based on data
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% composition
Empirical formulas
Molecular formulas
Chemistry Essential Standard
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2.2.5 To analyze quantitatively the composition
of a substance (empirical formula, molecular
formula, percent composition, and hydrates)
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Calculate empirical formula from mass or % composition from
experimental data
Calculate molecular formula from empirical formula using
molecular weight
Determine the percentage composition by mass of a given
compound
Perform calculations based on percent composition
Determine the composition of hydrates using experimental data
Molar Mass for Compounds
Molar Mass for Compounds
Names:
Molar Mass for Compounds
Names:
Practice
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What is the molar mass of Magnesium oxide?
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What is the number of moles of 60 g of Mg?
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How many moles are in 40 g of O?
CH₄
Mole
Ammonia side for homework
Methane
1)
What is the molar mass of CH₄?
2)
How many moles are present in 34 grams of
CH₄?
3)
How many grams are in 11.5 moles of CH₄?
4)
How many moles are there in 3.4 x
10²⁴ molecules of CH₄?
5)
How many molecules are in 8.5 moles of CH₄?
Mole calculations- methane
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6) How many molecules are in 300 grams of
CH₄?
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7) How many grams are in 5.2 x
10²⁴ molecules of CH₄?
Moles & mass (small sheet)
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25 g NaCl
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2.5 moles NaCl
Hydrate:
Copper II Sulfate – Penta Hydrate
35 grams of CuSO₄⁃5H₂O
3.2 moles of CuSO₄⁃5H₂O
See Mass and Moles Worksheet
Calculations based on Compounds
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Percent composition of each component in a
compound
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Empirical Formula: formula derived from
experimental data
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Based on mass
Smallest possible whole number ratio of
subscripts
Molecular Formula: actual number of atoms
of each element (actual subscripts)
Percent Composition – by mass
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Show the contribution of each component to
the mass of the compound
Applies to all compounds
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Nuts & Bolts/Beans
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Determining % composition
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Magnesium chloride
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Magnesium oxide
Determining % composition
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Magnesium carbonate
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Magnesium nitrate
Write the steps to determine %
composition
1. First,
2. For each type of atom, the % is calculated
by:
3. The answers are checked by …
Video segment
Molecular vs. Empirical Formulas
Molecular Formula
Empirical Formula
H2 O
CH3COOH
CH2O
C6H12O6
By looking at the
compounds above,
Predict what type of
compounds are used
Empirical Formula
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Based on analytical data from an unknown
sample
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Steps:
Percent to mass
Mass to mole
Divide by small
Multiply ‘til whole
Empirical formula: steps
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Example 1. A compound consists of 72.2%
magnesium and 27.8% nitrogen by mass.
What is the empirical formula?
Percent to mass
Mass to mole
Divide by small
Multiply ‘til whole
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A compound is analyzed and found to contain
68.54% carbon, 8.63% hydrogen, and
22.83% oxygen. The molecular weight of the
compound is known to be approximately 140
g/mol. What is the empirical formula?
Percent to
mass
Mass to mole
Divide by
small
Multiply ‘til
whole
Video: Empirical formulas
Molecular formulas
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To calculate molecular formulas, you must
know:
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Empirical Formula
Molecular mass of the compound
Empirical formula?
Molecular mass?
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A 1.50 g sample of hydrocarbon undergoes
complete combustion to produce CO₂ and H₂O.
The empirical formula of this compound is CH₃.
Its molecular mass has been determined to be
about 78. What is the molecular formula?
Empirical formula?
Molecular mass?
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Caffeine has the following percent
composition: carbon 49.48%, hydrogen
5.19%, oxygen 16.48% and nitrogen 28.85%.
Its molecular mass is 194.19 g/mol. What is
its molecular formula?