Chemistry: An Atoms-Focused Approach
Chemistry: An Atoms-Focused Approach
14th Edition
ISBN: 9780393912340
Author: Thomas R. Gilbert, Rein V. Kirss, Natalie Foster
Publisher: W. W. Norton & Company
Question
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Chapter 7, Problem 7.5VP
Interpretation Introduction

To find:

Which two hydrocarbons with the molecular structures shown in Figure P7.5 have the same percent composition?

Expert Solution & Answer
Check Mark

Answer to Problem 7.5VP

Solution:

Molecules (b) C2H4 and (d) C6H12 have same percent composition.

Explanation of Solution

1) Formula:

Percent composition is the percent by mass of an element in a compound:

Percent composition of element= Mass of elementMolecular mass*100

2) Calculations:

In the given Figure P7.5 black sphere represents C  atoms and white sphere represents H  atoms.

a) Molecule (a) contains six C  atoms and six H  atoms i.e. molecular formula is C6H6

Mass of 6 atoms C=6 atoms C×12.01 amu1  atom C=72.06 amu

Mass of 6 atoms H=6 atoms H×H= 6.048 amu

Molecular mass of C6H6=72.06 amu+6.048 amu= 78.108 amu.

Percent composition of C= Mass of CMolecular mass *100

= 72.0678.108*100=92.26%

Percent composition of H= Mass of HMolecular mass *100

= 6.04878.108*100=7.74%

b) Molecule (b) contains two C  atoms and four H  atoms i.e. molecular formula is C2H4

Mass of 2 atoms  C=2 atoms C×12.01 amu1  atom C=24.02 amu

Mass of 4 atoms H=4 atoms H×1.008 amu1  atom H= 4.032 amu

Molecular mass of C2H4=24.02 amu+4.032 amu=28.052 amu.

Percent composition of C= 24.0228.052*100=85.63%

Percent composition of H= 4.032 28.052*100=14.37%

c) Molecule (c) contains three C atoms and eight H  atoms i.e. molecular formula is C3H8

Mass of 3 atoms  C=3 atoms C×12.01 amu1  atom C=36.03 amu

Mass of 8 atoms H=8 atoms H×1.008 amu1  atom H=8.064 amu

Molecular mass of C3H8=8.064 amu+36.03  amu=44.094 amu.

Percent composition of C= 36.03 44.094*100=%

Percent composition of H= 8.06444.094*100=18.29%

d) Molecule (d) contains six C atoms and twelve H atoms i.e. molecular formula is C6H12

Mass of 6 atoms C=6 atoms C×12.01 amu1  atom C=72.06 amu

Mass of 12 atoms H=12 atoms H×1.008 amu1  atom H= 12.096 amu

Molecular mass of C6H12=72.06 amu+12.096 amu= 84.156 amu.

Percent composition of C= 72.0684.156*100=85.63%

Percent composition of H= 12.09684.156*100=14.37%

Therefore, molecule (b) and (d) have same percent composition.

Conclusion:

First, we calculate the mass of the number of atoms of C and H, and then calculate the percent composition of C and H using molecular mass of compound.

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Chapter 7 Solutions

Chemistry: An Atoms-Focused Approach

Ch. 7 - Prob. 7.11QACh. 7 - Prob. 7.12QACh. 7 - Prob. 7.13QACh. 7 - Prob. 7.14QACh. 7 - Prob. 7.15QACh. 7 - Prob. 7.16QACh. 7 - Prob. 7.17QACh. 7 - Prob. 7.18QACh. 7 - Prob. 7.19QACh. 7 - Prob. 7.20QACh. 7 - Prob. 7.21QACh. 7 - Prob. 7.22QACh. 7 - Prob. 7.23QACh. 7 - Prob. 7.24QACh. 7 - Prob. 7.25QACh. 7 - Prob. 7.26QACh. 7 - Prob. 7.27QACh. 7 - Prob. 7.28QACh. 7 - Prob. 7.29QACh. 7 - Prob. 7.30QACh. 7 - Prob. 7.31QACh. 7 - Prob. 7.32QACh. 7 - Prob. 7.33QACh. 7 - Prob. 7.35QACh. 7 - Prob. 7.36QACh. 7 - Prob. 7.37QACh. 7 - Prob. 7.38QACh. 7 - Prob. 7.39QACh. 7 - Prob. 7.40QACh. 7 - Prob. 7.41QACh. 7 - Prob. 7.42QACh. 7 - Prob. 7.43QACh. 7 - Prob. 7.44QACh. 7 - Prob. 7.45QACh. 7 - Prob. 7.46QACh. 7 - Prob. 7.47QACh. 7 - Prob. 7.48QACh. 7 - Prob. 7.49QACh. 7 - Prob. 7.50QACh. 7 - Prob. 7.51QACh. 7 - Prob. 7.52QACh. 7 - Prob. 7.53QACh. 7 - Prob. 7.54QACh. 7 - Prob. 7.55QACh. 7 - Prob. 7.56QACh. 7 - Prob. 7.57QACh. 7 - Prob. 7.58QACh. 7 - Prob. 7.59QACh. 7 - Prob. 7.60QACh. 7 - Prob. 7.61QACh. 7 - Prob. 7.62QACh. 7 - Prob. 7.63QACh. 7 - Prob. 7.64QACh. 7 - Prob. 7.65QACh. 7 - Prob. 7.66QACh. 7 - Prob. 7.67QACh. 7 - Prob. 7.68QACh. 7 - Prob. 7.69QACh. 7 - Prob. 7.70QACh. 7 - Prob. 7.71QACh. 7 - Prob. 7.72QACh. 7 - Prob. 7.73QACh. 7 - Prob. 7.74QACh. 7 - Prob. 7.75QACh. 7 - Prob. 7.76QACh. 7 - Prob. 7.77QACh. 7 - Prob. 7.78QACh. 7 - Prob. 7.79QACh. 7 - Prob. 7.80QACh. 7 - Prob. 7.81QACh. 7 - Prob. 7.82QACh. 7 - Prob. 7.83QACh. 7 - Prob. 7.84QACh. 7 - Prob. 7.85QACh. 7 - Prob. 7.86QACh. 7 - Prob. 7.87QACh. 7 - Prob. 7.88QACh. 7 - Prob. 7.89QACh. 7 - Prob. 7.90QACh. 7 - Prob. 7.91QACh. 7 - Prob. 7.92QACh. 7 - Prob. 7.93QACh. 7 - Prob. 7.94QACh. 7 - Prob. 7.95QACh. 7 - Prob. 7.96QACh. 7 - Prob. 7.97QACh. 7 - Prob. 7.98QACh. 7 - Prob. 7.99QACh. 7 - Prob. 7.100QACh. 7 - Prob. 7.101QACh. 7 - Prob. 7.102QACh. 7 - Prob. 7.103QACh. 7 - Prob. 7.104QACh. 7 - Prob. 7.105QACh. 7 - Prob. 7.106QACh. 7 - Prob. 7.107QACh. 7 - Prob. 7.108QACh. 7 - Prob. 7.109QACh. 7 - Prob. 7.110QA
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