Concept explainers
Anthraquinone contains only carbon, hydrogen, and oxygen. When 4.80 mg anthraquinone is burned, 14.2 mg CO2 and 1.65 mg H2O are produced. The freezing point of camphor is lowered by 22.3°C when 1.32 g anthraquinone is dissolved in 11.4 g camphor. Determine the empirical and molecular formulas of anthraquinone.
Interpretation: The empirical formula and molecular formula of Anthraquinone has to be determined.
Concept Introduction:
The ratio of the elements present in a compound and not the arrangement of the atoms are called as Empirical formula
Molecular formula is the representation of sum of number of atoms and molecules, not their arrangement in structure.
Answer to Problem 132IP
The empirical formula of Anthraquinone is
The molecular formula of Anthraquinone is
Explanation of Solution
Record the data
Mass of Carbon dioxide =
Mass of Water =
Freezing point of Camphor =
Mass of Anthraquinone burned =
Mass of Anthraquinone Dissolved =
Mass of Camphor =
To calculate the mass percent of Carbon, Hydrogen and Oxygen
Atomic mass of Carbon =
Molar mass of Carbon dioxide =
Atomic mass of Hydrogen =
Molar mass of Water =
Mass of Carbon =
Mass percentage of Carbon =
=
Mass of Hydrogen =
Mass percentage of Hydrogen =
=
Mass percentage of Oxygen =
=
Mass percentage of Carbon =
Mass percentage of Water =
Mass percentage of Oxygen =
To calculate the empirical formula
Mass percentage of Carbon =
Mass percentage of Hydrogen =
Mass percentage of Oxygen =
Out of
Therefore, the empirical formula is
Record the given info
Freezing point of Camphor =
Molal freezing point depression constant =
Mass of Anthraquinone burned =
Mass of Anthraquinone Dissolved =
Mass of Camphor =
To calculate the mass of Anthraquinone (m),
Molal of Anthraquinone =
Moles of Anthraquinone =
=
Moles of Anthraquinone =
To calculate the molar mass
Moles of Anthraquinone =
Mass of Anthraquinone Dissolved =
Molar mass of Anthraquinone =
=
To determine the Molecular formula of Anthraquinone
Empirical formula mass =
Molar mass of Anthraquinone =
Molar mass of Anthraquinone is twice the empirical mass of Anthraquinone, therefore the molecular mass of Anthraquinone is
Molecular Mass of Anthraquinone =
The moles of individual elements were calculated by using the mass percentages to their molar masses. The moles of the individual elements were divided by smallest ratio of moles and approximated to determine the empirical formula. The empirical formula was found to be
The molecular mass of Anthraquinone is calculated by using the molar mass and empirical formula mass. The molecular mass of Anthraquinone was
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