How do i find the empirical and molecular formulas of benzene?
By admin on Dec 27, 2009 in Chemistry
vbchick757 asked:
Benzene contains only carbon and hydrogen and has a molar mass of 78.1 g/mol. Analysis shows the compound to be 7.73% by mass. Find the empirical and molecular formulas of benzene.
Benzene contains only carbon and hydrogen and has a molar mass of 78.1 g/mol. Analysis shows the compound to be 7.73% by mass. Find the empirical and molecular formulas of benzene.
On Dec 28, 2009, Johnny D said:
I’m assuming you meant to say “7.73% hydrogen by mass.”
7.73 g H x 1 mol H/1 g H=7.73 mol H
100-7.73=92.27
92.27 g C x 1 mol C/12 g C=7.69 mol C
C=7.69/7.69=1
H=7.73/7.69=1
Empirical formula: CH
CH=13 g/mol
78.1/13=6
Molecular formula=6(CH)=C6H6
On Dec 28, 2009, vicinic said:
you missed a word after 7.73%. I’ll add the word hydrogen.
so 7.73% of the 78.1 is in hydrogen. That means that their is 6.03 grams of H for every 78.1. divide the 6.03 by the Mw of H and you get 5.999 or 6 H molecules.
The remaining mass is carbons , so 78.1 – 6.03 leaves 72 or so. Divide that by the mole wt C and you get 6, therefore there are 6 carbons and 6 hydrogens.
C6H6.