   Chapter 2, Problem 151GQ

Chapter
Section
Textbook Problem

Polystyrene can be prepared by heating styrene with tribromobenzoyl peroxide in the absence of air. A sample prepared by this method has the empirical formula Br3C6cH3(C8H8)n, where the value of n can vary from sample to sample. If one sample has 0.105% Br, what is the value of n?

Interpretation Introduction

Interpretation: The value of n in the empirical formula of the given compound Br3C6H3(C8H8)n should be determined if the sample has 0.105%Br

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Moles: One mole is equivalent to the mass of the substance consists same number of units equal to the atoms present in 12g of 12C.
• From given mass of substance moles could be calculated by using the following formula,

Molesofsubstance GivenmassofsubstanceMolecularmass

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

A sample of polystyrene was prepared by heating styrene with tribromobenzoyl peroxide in the absence of air and the empirical formula of the compound is Br3C6H3(C8H8)n.

If the sample contains 0.105%Br the value of n in the empirical formula of the compound can be determined as follows,

Molecular mass of the Bromine in the compound is 3×79.9040molarmassofBr=239.7g/mol

Molecular mass of  Br3C6H3=314.7g/mol

Molar mass of C8H8         =  104g/mol

Molecular mass of the given compound Br3</

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