   Chapter 2, Problem 144GQ

Chapter
Section
Textbook Problem

Which of the following statements about 57.1 g of octane, C8H18 is (are) not true?(a) 57.1 g is 0.500 mol of octane.(b) The compound is 84.1% C by weight.(c) The empirical formula of the compound is C4H9).(d) 57.1 g of octane contains 28.0 g of hydrogen atoms.

Interpretation Introduction

Interpretation: From the given statements the incorrect statement regarding about 57.1g of octane C8H18 should be determined.

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Mass percentage is one way to represent the concentration of an element in a compound or a component in a mixture. Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
• Equation for number moles from mass and molar mass,

Numberofmoles=MassingramsMolarmass

Explanation

Reason for the correct answer:

Given,

57.1g Of octane C8H18 the mass percentage of hydrogen in the compound is 15.75%.

(18gH114.23g×100%) = 15.75%

The mass of hydrogen atoms in 57.1g of octane C8H18 is,

15.75100×57.1=8.9g

Therefore, the statement d 57.1gof octane contains 28.0gof hydrogen atoms is incorrect about 57.1g of octane C8H18.

Hence, the correct option is (d).

Reasons for the incorrect statements:

Given

Statement a is correct because 57.1gofoctaneis0.500moloctane

Number of moles in octane =   57.1g114.23g/mol=0.5mol

Given statement b the compound is 84.1% C by weight.

Weight percentage of Carbon in 57

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