   Chapter 4.4, Problem 4.5CYU

Chapter
Section
Textbook Problem

A 0.1342-g sample of a compound composed of C, H, and O was burned in oxygen and 0.240 g of CO2 and 0.0982 g of H2O was isolated. What is the empirical formula of the compound? If the experimentally determined molar mass is 74.1 g/mol, what is the molecular formula of the compound?

Interpretation Introduction

Interpretation:

The empirical formula and molecular formula of the given compound 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 masses the of CO2andH2O amount of carbon and hydrogen present in the sample can be determined as follows,

Thus, amount of CandH isolated from the combustion are,

0.240gCO2×1molCO244.010gCO2×1molC1molCO2×12.01gC1molC=0.06549gC0.0982gH2O×1molH2O18.015gH2O×2molH1molH2O×1.008gH1molH=0.01099gmol H

The mass of oxygen in the sample can be determined from the mass of original sample and the masses of carbon and oxygen in the sample as follows,

Massofsample=0.1342g=0.06549gC+0.01099gH+xgO

MassofO=0.05772gO

Amount of Carbon, Hydrogen and Oxygen can be calculated from its mass and molar mass as follows,

Amountofcarbon=0.06549gC×1molC12.01gC=0

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