What is the empirical formula for a compound containing only carbon and hydrogen if it is known to contain 84.21% carbon? If the molar mass is 114 g/mol, what is the molecular formula of this compound?
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What is the empirical formula for a compound containing only carbon and hydrogen if it is known to contain 84.21% carbon? If the molar mass is 114 g/mol, what is the molecular formula of this compound?
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Answer:
Since the compound contains carbon & hydrogen only, it’s a hydrocarbon. As the Carbon is 84.21%, the hydrogen must be 100–84.21=15.79%.
To get the total number of each atom in the compound, divide the % by the molar mass of each atom.
Carbon = 84.21 divided by 12.01= 7.012 & Hydrogen = 15.79 divided by 1 = 15.79
By approximation, C=7 & H=16, and this gives the simplest ratio of each atom in the compound, ie, it’s Empirical Formula, EF=C7H16
The molar mass of the compound is 114g/mol. Using this information, we can work out the molecular formula as follows:
Molecular Formula, MF= (C7H16) times X=114.
ie, (12.01 X 7 + 16 X 1) times X = 114.
(84.07+16) times X = 114.
Therefore X= 114 divided by 100.07 = 1.1392, which is approximately equal to 1. ie, the MF is C7H16 & the name is heptane which is an Alkane hydrocarbon.
Explanation:
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