Finding Emperical and Molecular Formulas (3.3.1) Flashcards
• Analysis by mass is used to determine the ratio of elements in a sample.
• Analysis by mass is used to determine the ratio of elements in a sample.
• The empirical formula is the chemical formula of a compound written with the simplest ratio of elements.
• The empirical formula is the chemical formula of a compound written with the simplest ratio of elements.
• The molecular formula is the exact atomic formula of a compound.
• The molecular formula is the exact atomic formula of a compound.
Chemists are often called upon to identify unknown
substances. Analysis by mass is used to determine
the ratio of elements in a sample.
Analysis by mass gives the percent composition
of each element in a compound.
In this example, the compound was found to contain
39.9% carbon, 6.70% hydrogen, and 53.4% oxygen.
Chemists are often called upon to identify unknown
substances. Analysis by mass is used to determine
the ratio of elements in a sample.
Analysis by mass gives the percent composition
of each element in a compound.
In this example, the compound was found to contain
39.9% carbon, 6.70% hydrogen, and 53.4% oxygen.
The percent composition can be used to determine
the empirical formula of a compound.
An empirical formula is a chemical formula that
indicates only the relative numbers of atoms of
each type in a molecule. Subscripts in empirical
formulas are always the smallest integer ratios for
the atoms involved. Empirical formulas show the
relative molar ratio of each element in a compound
to the other elements in the compound.
The empirical formula can be determined from the
percent composition by assuming a 100 gram
sample, and converting the percent composition to
masses of each element. These masses can be
converted to moles using the molar mass of each
element. Finally, the moles are converted to the
simplest molar ratio by dividing by the smallest
number of moles.
In this example, the empirical formula is C1H2O1 or
just CH2O. However, this is the empirical formula of
many different compounds, such as formaldehyde
(CH2O), acetic acid (C2H4O2), and glycerine
(C3H6O3).
The percent composition can be used to determine
the empirical formula of a compound.
An empirical formula is a chemical formula that
indicates only the relative numbers of atoms of
each type in a molecule. Subscripts in empirical
formulas are always the smallest integer ratios for
the atoms involved. Empirical formulas show the
relative molar ratio of each element in a compound
to the other elements in the compound.
The empirical formula can be determined from the
percent composition by assuming a 100 gram
sample, and converting the percent composition to
masses of each element. These masses can be
converted to moles using the molar mass of each
element. Finally, the moles are converted to the
simplest molar ratio by dividing by the smallest
number of moles.
In this example, the empirical formula is C1H2O1 or
just CH2O. However, this is the empirical formula of
many different compounds, such as formaldehyde
(CH2O), acetic acid (C2H4O2), and glycerine
(C3H6O3).
The molecular formula is the exact atomic formula
of a compound. The subscripts in the molecular
formula of a compound are integer multiples of the
subscripts in the empirical formula of that
compound.
Mass spectrometry can be used to determine the
molar mass (the molecular formula weight) of the
compound. The ratio of the molecular formula
weight to the empirical formula weight is an integer
(n). This integer is the number that the subscripts of
the empirical formula must be multiplied by to yield
the molecular formula.
In this example, the empirical formula is CH2O. The
molecular formula is a multiple of that formula,
CnH2nOn. The integer n is found to be 2 by dividing
the molecular formula weight by the empirical
formula weight. Therefore, the molecular formula is
C2H4O2.
The molecular formula is the exact atomic formula
of a compound. The subscripts in the molecular
formula of a compound are integer multiples of the
subscripts in the empirical formula of that
compound.
Mass spectrometry can be used to determine the
molar mass (the molecular formula weight) of the
compound. The ratio of the molecular formula
weight to the empirical formula weight is an integer
(n). This integer is the number that the subscripts of
the empirical formula must be multiplied by to yield
the molecular formula.
In this example, the empirical formula is CH2O. The
molecular formula is a multiple of that formula,
CnH2nOn. The integer n is found to be 2 by dividing
the molecular formula weight by the empirical
formula weight. Therefore, the molecular formula is
C2H4O2.
Even the molecular formula does not uniquely
identify the compound. C2H4O2 could be vinegar,
but it could also be other compounds. Further tests
would have to be performed to uniquely identify the
compound.
Even the molecular formula does not uniquely
identify the compound. C2H4O2 could be vinegar,
but it could also be other compounds. Further tests
would have to be performed to uniquely identify the
compound.
