   Chapter 22, Problem 160IP

Chapter
Section
Textbook Problem

# Helicenes are extended fused polyaromatic hydrocarbons that have a helical or screw-shaped structure.a. A 0.1450-g sample of solid helicene is combusted in air to give 0.5063 g CO2. What is the empirical formula of this helicene?b. If a 0.0938-g sample of this helicene is dissolved in 12.5 g of solvent to give a 0.0175 M solution, what is the molecular formula of this helicene?c. What is the balanced reaction for the combustion of this helicene?

(a)

Interpretation Introduction

Interpretation: The empirical formula and the molecular formula of the given helicene are to be calculated. The balanced chemical reaction for the combustion of helicene is to be stated.

Concept introduction: Helicines are defined as the polycyclic aromatic compounds in which the aromatic ring is annulated to provide helically shaped molecule. The molecular formula of any organic compound is determined by using empirical formula when the percent of each element is given in the compound.

To determine: The empirical formula of the given helicene.

Explanation

Explanation

The empirical formula of the given helicene is C5H3 .

Helicene is an aromatic compound so it must contain carbon and hydrogen atoms.

Given

Weight of CO2 is 0.5063 g .

Weight of compound is 0.1450 g .

The weight of carbon is calculated by using the formula,

Weight of carbon=Weight of CO2×Molecular weight of carbonMolecular weightof CO2

The molar mass of carbon is 12g/mol .

The molar mass of carbon dioxide is 44g/mol .

Substitute the value of weight of CO2 , molecular weight of carbon and CO2 to calculate the weight of carbon in the above formula.

Weight of carbon=Weight of CO2×Molecular weight of carbonMolecular weightof CO2=0.5063 g×12 g/mol44 g/mol=0.1380 g

The weight of carbon is 0.1380 g .

Therefore the weight of hydrogen is calculated as,

Weight of hygrogen=Weight of compoundWeight of carbon=0.1450 g0.1380 g=0.007 g

Therefore the number of moles of carbon and hydrogen is calculated by the formula,

Numberofmoles=GivenmassMolarmass

Substitute the value of the given mass and the molar mass, to calculate the number of moles of carbon and hydrogen in the above equation

(b)

Interpretation Introduction

Interpretation: The empirical formula and the molecular formula of the given helicene are to be calculated. The balanced chemical reaction for the combustion of helicene is to be stated.

Concept introduction: Helicines are defined as the polycyclic aromatic compounds in which the aromatic ring is annulated to provide helically shaped molecule. The molecular formula of any organic compound is determined by using empirical formula when the percent of each element is given in the compound.

To determine: The molecular formula of the given helicene.

(c)

Interpretation Introduction

Interpretation: The empirical formula and the molecular formula of the given helicene are to be calculated. The balanced chemical reaction for the combustion of helicene is to be stated.

Concept introduction: Helicines are defined as the polycyclic aromatic compounds in which the aromatic ring is annulated to provide helically shaped molecule. The molecular formula of any organic compound is determined by using empirical formula when the percent of each element is given in the compound.

To determine: The balanced chemical reaction for the combustion of helicene.

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