Chapter 23, Problem 7QAP

Interpretation Introduction

Interpretation:

From the given table, the polymer with the largest molar mass needs to be determined. Assuming the number of monomer units are same in all the polymers.

Concept introduction:

A polymer is a long chain consists of large number of monomer units. In a polymer, the monomers are linked to each other in a continuous or repetitive manner. These monomer units are linked to each other either through the formation of peptide linkage, glycosidic linkage or by removal of any moiety such as a water molecule. Polyvinyl chloride, Bakelite and polystyrene are some of the examples of polymers.

Answer to Problem 7QAP

The molar mass of styrene is largest of all and thus polystyrene has the largest molar mass.

Explanation of Solution

If all the polymers contain the same number of monomer units, the molar mass of polymers can be compared by comparing the molar mass of monomers in it.

(1)

In the table mentioned in the problem, the 1^st polymer contains ethylene as a monomer unit. Ethylene consists of 2 carbon and 4 hydrogen atoms. The molar mass can be calculated as follows:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\end{array}\right)$

Putting the values,

$\begin{array}{c}\text{Molar mass of monomer unit = 2 }\times \text{ 12 g/mol + 4 }\times \text{ 1 g/mol}\\ \text{= 28 g/mol}\end{array}$

(2)

The 2^nd polymer shown in table consists of propylene as a monomer unit. Propylene consists of 3 carbon and 6 hydrogen atoms.

The molar mass can be calculated as follows:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\end{array}\right)$

Putting the values,

$\text{Molar mass of monomer unit = 3 }\times \text{ 12 + 6 }\times \text{ 1 = 42 g /mol}$

(3)

The 3^rd polymer shown in table consists of vinyl chloride as monomer unit. Vinyl chloride consists of 2 carbon and 3 hydrogen and 1 chlorine atom.

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\\ \text{+ }\left(\text{Number of Cl}\right)\left(\text{molar mass of Cl}\right)\end{array}\right)$

Putting the values,

$\begin{array}{c}\text{Molar mass of monomer unit = 2 }\times \text{ 12 + 3 }\times \text{ 1 + 1 }\times \text{ 35 }\\ \text{= 62 g /mol}\end{array}$

(4)

The 4^th polymer shown in table consists of acrylonitrile as monomer unit. Acrylonitrile consists of 3 carbon, 3 hydrogen and 1 nitrogen atoms. The molar mass can be calculated as follows:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\\ \text{+ }\left(\text{Number of N}\right)\left(\text{molar mass of N}\right)\end{array}\right)$

Putting the values,

$\begin{array}{c}\text{Molar mass of monomer unit = 3 }\times \text{ 12 + 3 }\times \text{ 1 + 1 }\times \text{ 14 }\\ \text{= 53 g /mol}\end{array}$

(5)

The 5^th polymer shown in table consists of styrene as monomer unit. Styrene consists of 8 carbon and 8 hydrogen atoms. The molar mass can be calculated as follows:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\end{array}\right)$

$\begin{array}{c}\text{Molar mass of monomer unit = 8 }\times \text{ 12 + 8 }\times \text{ 1 }\\ \text{= 104 g /mol}\end{array}$

(6)

The 6^th polymer shown in table consists of methyl methacrylate as monomer unit. Methacrylate consists of 2 carbon and 2 oxygen atoms. The molar mass can be calculated as follow:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of H}\right)\left(\text{molar mass of H}\right)\\ \text{+ }\left(\text{Number of O}\right)\left(\text{molar mass of O}\right)\end{array}\right)$

Putting the values,

$\begin{array}{c}\text{Molar mass of monomer unit = 5 × 12+ 8 × 1 + 2 × 16 }\\ \text{= 101 g /mol}\end{array}$

(7)

The 7^th polymer shown in table consists of tetrafluoroethylene as monomer unit. Tetrafluoroethylene consists of 2 carbon and 4 fluorine atoms. The molar mass can be calculated as follows:

$\text{Molar mass of monomer unit = }\left(\begin{array}{l}\left(\text{Number of C}\right)\left(\text{molar mass of C}\right)\\ \text{+ }\left(\text{Number of F}\right)\left(\text{molar mass of F}\right)\end{array}\right)$

Putting the values,

$\begin{array}{c}\text{Molar mass of monomer unit= 2 }\times \text{ 12 + 4 }\times \text{ 18 }\\ \text{= 100 g /mol}\end{array}$

The molar mass of styrene (5) is largest of all and thus polystyrene have the largest molar mass.

Conclusion

Thus, the molar mass of polystyrene is maximum.