   Chapter 2, Problem 89PS

Chapter
Section
Textbook Problem

Cumene, a hydrocarbon, is a compound composed only of C and H. It is 89.94% carbon, and its molar mass is 120.2 g/mol. What are the empirical and molecular formulas of cumene?

Interpretation Introduction

Interpretation:

The empirical formula and molecular formula of the cumene is to be determined if the molar mass is 120.2g/mol.

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Equation for finding Molecular formula from the empirical formula,

MolarmassEmpiricalformula mass × Empirical formula

• Equation for number moles from mass and molar mass,

Numberofmoles=MassingramsMolarmass

• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
Explanation

Mass percent of carbon, and hydrogen in cumene is given as 89.94% and 10089.94=10.06%.

Mass percent of an element means, 100g of compound contains that mass percent of an element in grams. Therefore, mass of carbon and hydrogen are 89.94g and 10.06g respectively in 100g of cumene.

Equation for number moles from mass and molar mass is,

Numberofmoles=MassingramsMolarmass

Therefore,

The number of moles of carbon is,

Numberofmoles=89.94g12.01g/mol=7.48mol

The number of moles of hydrogen is,

Numberofmoles=10

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