Chapter 4, Problem 91GQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Benzoquinone, a chemical used in the dye industry and in photography, is an organic compound containing only C, H, and O. What is the empirical formula of the compound if 0.105 g of the compound gives 0.257 g of CO2 and 0.0350 g of H2O when burned completely in oxygen?

Interpretation Introduction

Interpretation:

The empirical formula of benzoquinone has to be determined.

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

• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mol (g/mol).
Explanation

Given that 0.105â€‰g of benzoquinone burns in oxygen then give 0.257â€‰â€‰g of CO2 and 0.0350â€‰g of H2O

From the given masses the amount of CO2 and H2O can be calculated.

Thus, amount of CO2 and H2O are,

â€‚Â 0.257â€‰â€‰gâ€‰â€‰CO2â€‰Ã—â€‰1â€‰molâ€‰CO244.010â€‰gâ€‰CO2â€‰=â€‰0.00583molâ€‰CO20.0350â€‰gâ€‰H2Oâ€‰Ã—1â€‰molâ€‰H2O18.015â€‰gâ€‰H2Oâ€‰=â€‰0.00194â€‰molâ€‰H2O

For every mole of CO2 isolated, 1 mol of Carbon must have been present in the benzoquinone.

Hence,

â€‚Â 0.00583â€‰molâ€‰CO2â€‰Ã—1 mol C in menthol1 mol CO2â€‰=â€‰0.00583â€‰molâ€‰C

For every mole of H2O isolated, 2 mol of Hydrogen must have been present in the unknown compound.

Therefore,

â€‚Â 0.00194â€‰molâ€‰H2Oâ€‰Ã—2 mol H in menthol1 mol H2Oâ€‰=â€‰0.00388â€‰molâ€‰H

The mass of the substance can be determined by multiplying the amount of substance with its molar mass.

The mass of carbon and Hydrogen are 0.0699gâ€‰â€‰andâ€‰â€‰0.0039gâ€‰ respectively

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