Anthracene, a hydrocarbon obtained from coal, has an empericalformula of C7H5. To find its molecularformula, you dissolve 0.500g in 30.0g of benzene. The boilingpoint of pure benzene is 80.10 o C, whereas the solutionhas a boiling point of 80.34 oC . What is the molecularformula of anthracene?

Anthracene, a hydrocarbon obtained from coal, has an empericalformula of C7H5. To find its molecularformula, you dissolve 0.500g in 30.0g of benzene. The boilingpoint of pure benzene is 80.10 o C, whereas the solutionhas a boiling point of 80.34 oC . What is the molecularformula of anthracene?

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asked 2021-01-31
Anthracene, a hydrocarbon obtained from coal, has an empericalformula of C7H5. To find its molecularformula, you dissolve 0.500g in 30.0g of benzene. The boilingpoint of pure benzene is 80.10 o C, whereas the solutionhas a boiling point of 80.34 oC . What is the molecularformula of anthracene?

Answers (1)

2021-02-01
?Tb= Kbm; Kb= 2.53oC/m for benzene m =?Tb/Kb \(\displaystyle={\frac{{{\left({80.34}{o}{C}-{80.10}{o}{C}\right)}}}{{{\left({2.53}{o}\frac{{C}}{{m}}\right)}}}}={0.095}{m}={0.095}\) moles anthracene/1000 g solvent
moles of anthracene = (0.095 moles/1000g benzene)(30.0g benzene) 2.85\times 10-3moles
MW anthracene = \(\displaystyle{\frac{{{0.500}{g}}}{{{2.85}\times{10}-{3}{m}{o}\le{s}}}}\) = 175.44g/mole
whole number to multiply subscripts in empirical formula =175.44/empirical formula weight anthracene = \(\displaystyle{\frac{{{175.44}}}{{{89}}}}\) = 1.97 =2
Molecular formula of anthracene is C14H10
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