Chemistry: An Atoms First Approach
Chemistry: An Atoms First Approach
2nd Edition
ISBN: 9781305079243
Author: Steven S. Zumdahl, Susan A. Zumdahl
Publisher: Cengage Learning
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Chapter 5, Problem 79E

Express the composition of each of the following compounds as the mass percents of its elements.

a. formaldehyde, CH2O

b. glucose, C6H12O6

c. acetic acid, HC2H3O2

(a)

Expert Solution
Check Mark
Interpretation Introduction

Interpretation: The percentage composition (by mass) of each element in the given compounds CH2O,C6H12O6 and HC2H3O2 is to be calculated.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

To determine: The percentage composition (by mass) of each element in formaldehyde (CH2O) compound.

Explanation of Solution

The atomic weight of carbon (C) is 12.01g/mol . In the compound CH2O , only one carbon atom is present. Hence, mass of carbon in CH2O is 12.01g/mol .

The atomic weight of oxygen (O) is 15.999g/mol . In the compound CH2O , only one oxygen atom is present. Hence, mass of oxygen in CH2O is 15.999g/mol .

The atomic weight of hydrogen (H) is 1.008g/mol . In the compound CH2O , two hydrogen atoms are present. Hence, mass of hydrogen in CH2O is,

2×1.008g/mol=2.016g/mol

The molar mass is the sum of mass of individual atoms present in it.

Hence, molar mass of CH2O is calculated as,

12.01g/mol+15.999g/mol+2.016g/mol=30.025g/mol

Formula

The mass percent of element is calculated as,

Mass%ofelement=MassofelementMolarmassofcompound                                         (1)

Substitute the values of mass of carbon and molar mass of CH2O in the above equation.

Mass%ofCatom=MassofCatomMolarmassofCH2O=(12.01g/mol30.025g/mol)×100=40.00%_

Substitute the values of mass of hydrogen and molar mass of CH2O in equation (1).

Mass%ofHatom=MassofHatomMolarmassofCH2O=(2.016g/mol30.025g/mol)×100=6.714%_

Substitute the values of mass of oxygen and molar mass of CH2O in equation (1).

Mass%ofOatom=MassofOatomMolarmassofCH2O=(15.999g/mol30.025g/mol)×100=53.28%_

The percentage composition (by mass) of carbon, hydrogen and oxygen is 40.00%_ , 6.714%_ and 53.28%_ respectively.

Conclusion

The percentage composition of any element is calculated by dividing the total mass of that element with molar mass of compound.

(b)

Expert Solution
Check Mark
Interpretation Introduction

Interpretation: The percentage composition (by mass) of each element in the given compounds CH2O,C6H12O6 and HC2H3O2 is to be calculated.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

To determine: The percentage composition (by mass) of each element in glucose (C6H12O6) compound.

Explanation of Solution

The atomic weight of carbon (C) is 12.01g/mol . In the compound C6H12O6 , six carbon atoms are present. Hence, mass of carbon in C6H12O6 is,

6×12.01g/mol=72.06g/mol

The atomic weight of oxygen (O) is 15.999g/mol . In the compound C6H12O6 , six oxygen atoms are present. Hence, mass of oxygen in C6H12O6 is,

6×15.999g/mol=95.994g/mol

The atomic weight of hydrogen (H) is 1.008g/mol . In the compound C6H12O6 , twelve hydrogen atoms are present. Hence, mass of hydrogen in C6H12O6 is,

12×1.008g/mol=12.096g/mol

The molar mass is the sum of mass of individual atoms present in it.

Hence, molar mass of C6H12O6 is calculated as,

72.06g/mol+95.994g/mol+12.096g/mol=180.15g/mol

Formula

The mass percent of element is calculated as,

Mass%ofelement=MassofelementMolarmassofcompound                                         (1)

Substitute the values of mass of carbon and molar mass of C6H12O6 in the above equation.

Mass%ofCatom=MassofCatomMolarmassofC6H12O6=(72.06g/mol180.15g/mol)×100=40.00%_

Substitute the values of mass of hydrogen and molar mass of C6H12O6 in equation (1).

Mass%ofHatom=MassofHatomMolarmassofC6H12O6=(12.096g/mol180.15g/mol)×100=6.714%_

Substitute the values of mass of oxygen and molar mass of C6H12O6 in equation (1).

Mass%ofOatom=MassofOatomMolarmassofC6H12O6=(95.994g/mol180.15g/mol)×100=53.28%_

Conclusion

The percentage composition of any element is calculated by dividing the total mass of that element with molar mass of compound.

(c)

Expert Solution
Check Mark
Interpretation Introduction

Interpretation: The percentage composition (by mass) of each element in the given compounds CH2O,C6H12O6 and HC2H3O2 is to be calculated.

Concept introduction: The atomic mass is defined as the sum of number of protons and number of neutrons.

Molar mass of a substance is defined as the mass of the substance in gram of one mole of that compound.

The molar mass of any compound can be calculated by adding of atomic weight of individual atoms present in it.

To determine: The percentage composition (by mass) of each element in acetic acid (HC2H3O2) compound.

Explanation of Solution

The atomic weight of carbon (C) is 12.01g/mol . In the compound HC2H3O2 , two carbon atoms are present. Hence, mass of carbon in HC2H3O2 is,

2×12.01g/mol=24.02g/mol

The atomic weight of oxygen (O) is 15.999g/mol . In the compound HC2H3O2 , two oxygen atoms are present. Hence, mass of oxygen in HC2H3O2 is,

2×15.999g/mol=31.998g/mol

The atomic weight of hydrogen (H) is 1.008g/mol . In the compound HC2H3O2 , four hydrogen atoms are present. Hence, mass of hydrogen in HC2H3O2 is,

4×1.008g/mol=4.032g/mol

The molar mass is the sum of mass of individual atoms present in it. Hence, molar mass of HC2H3O2 is calculated as,

24.02g/mol+31.998g/mol+4.032g/mol=60.05g/mol

Formula

The mass percent of element is calculated as,

Mass%ofelement=MassofelementMolarmassofcompound                                         (1)

Substitute the values of mass of carbon and molar mass of HC2H3O2 in the above equation.

Mass%ofCatom=MassofCatomMolarmassofHC2H3O2=(24.02g/mol60.05g/mol)×100=40.00%_

Substitute the values of mass of hydrogen and molar mass of HC2H3O2 in equation (1).

Mass%ofHatom=MassofHatomMolarmassofHC2H3O2=(4.032g/mol60.05g/mol)×100=6.72%_

Substitute the values of mass of nitrogen and molar mass of HC2H3O2 in equation (1).

Mass%ofOatom=MassofOatomMolarmassofC3H3N=(31.998g/mol60.05g/mol)×100=53.28%_

Conclusion

The percentage composition of any element is calculated by dividing the total mass of that element with molar mass of compound.

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Chapter 5 Solutions

Chemistry: An Atoms First Approach

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