Big Idea: Matter & Atoms
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Mass Percent
Empirical and Molecular Formulas
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Determine the Mass Percent of each element in 𝐹𝑒𝑇𝑖𝑂3 .
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A tablet contains 0.025 mg of Vitamin D. The
entire tablet, however, has a mass of 0.115 g.
Calculate the mass percent of vitamin D in
the tablet.
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A sample of potassium permanganate
𝐾𝑀𝑛𝑂4 is known to contain some impurities.
It is found that 𝐾 + makes up 19.24% of the
entire mass of the sample.
All of the 𝐾 + comes from the 𝐾𝑀𝑛𝑂4
compound. Find the mass percent of 𝐾𝑀𝑛𝑂4
in the sample.
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Molecular Formulas
◦ Chemical formulas that provide the actual number
of each type of atom in molecule.
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Empirical Formulas
◦ Chemical formulas that provide relative number of
each type of atom in molecule…a ratio in simplest
form)
Common Name
Molecular Formula
Empirical Formula
Hydrogen Peroxide
𝐻2 𝑂2
𝐻𝑂
Ethylene
𝐶2 𝐻4
𝐶𝐻2
Dextrose
𝐶6 𝐻12 𝑂6
𝐶𝐻2 𝑂
Common Name
Molecular Formula
Empirical Formula
Water
𝐻2 𝑂
𝐻2 𝑂
Acetylene
𝐶2 𝐻2
𝐶𝐻
Hydrazine
𝑁2 𝐻4
𝑁𝐻2
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A sample of caffeine was found to contain
49.5% carbon, 28.9% nitrogen, 16.5% oxygen,
5.1% hydrogen. Calculate the empirical
formula for caffeine.
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Molecular Formulas
◦ Chemical formulas that provide the actual number
of each type of atom in molecule.
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The molecular formula for hydrogen peroxide
is 𝐻2 𝑂2 .
Calculate the molecular formula of caffeine if
the molar mass of caffeine is 194.2 g/mol.
Determination of percent composition &
empirical formula of an organic compound
composed of carbon, hydrogen & oxygen
uses the combustion analysis method.
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A 2.04 g sample containing C, H & O
underwent combustion analysis. 4.49 g of
CO2 and 2.45 g H2O were produced.
Determine the empirical formula.
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Use stoichiometry to find the grams of carbon
and hydrogen.
◦ Subtract the total mass from the sum of the masses
of carbon & hydrogen to find the mass of oxygen.
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Find moles of carbon, hydrogen & oxygen.
Find the empirical formula.