   Chapter 4.4, Problem 4.4CYU ### Chemistry & Chemical Reactivity

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

#### Solutions

Chapter
Section ### Chemistry & Chemical Reactivity

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

# A 0523-g sample of the unknown compound CxHy was burned in air to give 1.612 g of CO2 and 0.7425 g of H2O. A separate experiment gave a molar mass for CxHy of 114 g/mol Determine the empirical and molecular formulas for the hydrocarbon.

Interpretation Introduction

Interpretation:

The empirical and molecular formula for the unknown hydrocarbon CxHy should 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

From the given masses the amount of CO2andH2O can be calculated.

Thus, amount of CO2andH2O isolated from the combustion are,

1.612gCO2×1molCO244.010gCO2=0.03662molCO20.7425gH2O×1molH2O18.015gH2O=0.04121molH2O

For every mole of CO2 isolated, 1 mol of C must have been present in the unknown compound.

So,

0.03662molCO2×1molCinunknown1molCO2=0.03662molC

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

Therefore,

0.04121molH2O×2molHinunknown1molH2O=0

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