Chapter 22, Problem 168CP

(a)

Interpretation Introduction

Interpretation: The two repeating units of ABS plastic assuming the three monomer units react in a $1:1:1$ mole ratio and in the same order as the monomers are to be drawn. The percent by mass of acrylonitrile, butadiene and styrene in the polymer sample is to be calculated and the relative numbers of monomer units in the given sample of ABS plastic is to be determined.

Concept introduction: The polymers (repeating structural units) are derived from the simple and reactive molecules, called as monomers. ABS plastic is a terpolymer of styrene, acrylonitrile and polybutadiene.

To determine: The structure of two repeating units of ABS plastic assuming the three monomer units react in a $1:1:1$ mole ratio and in the same order as the monomers.

Answer to Problem 168CP

Answer

The two repeating units of ABS plastic are shown in Figure 1.

Explanation of Solution

Explanation

The structure of the polymer of ABS plastic is shown in figure 1.

The reaction of Abs polymer synthesis is,

Figure 1

ABS plastic is a terpolymer synthesized by polymerizing styrene, acrylonitrile and polybutadiene. The chemical formula of ABS polymer is ${\left({\text{C}}_{\text{8}}{\text{H}}_{\text{8}}{\text{.C}}_{\text{4}}{\text{H}}_{\text{6}}{\text{.C}}_{\text{3}}{\text{H}}_{\text{3}}\text{N}\right)}_{\text{n}}$ whose structure of two repeating units of monomers is shown in Figure 1

(b)

Interpretation Introduction

Interpretation: The two repeating units of ABS plastic assuming the three monomer units react in a $1:1:1$ mole ratio and in the same order as the monomers are to be drawn. The percent by mass of acrylonitrile, butadiene and styrene in the polymer sample is to be calculated and the relative numbers of monomer units in the given sample of ABS plastic is to be determined.

Concept introduction: The polymers (repeating structural units) are derived from the simple and reactive molecules, called as monomers. ABS plastic is a terpolymer of styrene, acrylonitrile and polybutadiene.

To determine: The percent by mass of acrylonitrile, butadiene and styrene in the polymer sample.

Answer to Problem 168CP

Answer

The mass percent of acrylonitrile is $\underset{\_}{16.90\%}$.

The mass percent of butadiene is $\underset{\_}{17.22\%}$.

The mass percent of styrene is $\underset{\_}{33.18\%}$.

Explanation of Solution

Explanation

The mass percent of the three given monomers is calculated below.

Given

The mass of bromine to react completely with ABS plastic is $\text{0}\text{.605 g}$.

The mass of ABS plastic is $\text{1}\text{.20 g}$.

The molar mass of bromine is $158\text{g/mol}$.

The number of moles is calculated by the formula,

$\text{Number}\text{of}\text{moles}=\frac{\text{Given}\text{mass}}{\text{Molar}\text{mass}}$

Substitute the given value of the mass and molar mass of bromine in the above expression.

$\begin{array}{c}\text{Number}\text{of}\text{moles}\text{of}\text{bromine}=\frac{\text{Given}\text{mass}}{\text{Molar}\text{mass}}\\ =\frac{0.605\text{g}}{\text{158g/mol}}\\ =0.003829\text{mol}\end{array}$

Hence, each molecule in this polymer contains $0.003829\text{mol}$.

Therefore, $0.003829\text{mol}$ of bromine reacted with $0.003829\text{mol}$ of polymer.

The ABS plastic is constructed by equimolar ratio of the three molecules. Hence, each molecule is $0.003829\text{mol}$.

Therefore,

The mass of acrylonitrile, styrene and butadiene is calculated as,

The molar mass of acrylonitrile is $\text{53 g/mol}$.

The molar mass of butadiene is $\text{54 g/mol}$.

The molar mass of styrene is $\text{104 g/mol}$.

The mass of acrylonitrile, styrene and butadiene is calculated by using the formula,

$\text{Mass}=\text{Number of moles}\times \text{Molar mass}$.

Substitute the given value of the number of moles and molar mass of in the above expression.

For acrylonitrile,

$\begin{array}{c}\text{Mass of acrylonitrile}=\text{Number of moles}\times \text{Molar mass}\\ =\text{0}\text{.003829 mol}\times \text{53 g/mol}\\ =\text{0}\text{.2029 g}\end{array}$

For butadiene,

$\begin{array}{c}\text{Mass of butadiene}=\text{Number of moles}\times \text{Molar mass}\\ =\text{0}\text{.003829 mol}\times \text{54 g/mol}\\ =\text{0}\text{.2067 g}\end{array}$

For styrene

$\begin{array}{c}\text{Mass of styrene}=\text{Number of moles}\times \text{Molar mass}\\ =\text{0}\text{.003829 mol}\times 104\text{ g/mol}\\ =\text{0}\text{.3982 g}\end{array}$

Therefore,

Mass percent of acrylonitrile, styrene and butadiene is calculated as,

For acrylonitrile,

$\begin{array}{c}\text{Mass percent of acrylonitrile = }\frac{\text{0}\text{.2029}}{\text{1}\text{.20}}\text{×100}\\ \text{= }\underset{\_}{16.90\%}\end{array}$

For butadiene,

$\begin{array}{c}\text{Mass percent of butadiene = }\frac{\text{0}\text{.2067}}{\text{1}\text{.20}}\text{×100}\\ \text{= }\underset{\_}{17.22\%}\end{array}$

For styrene

$\begin{array}{c}\text{Mass percent of styrene = }\frac{\text{0}\text{.3982}}{\text{1}\text{.20}}\text{×100}\\ \text{= }\underset{\_}{33.18\%}\end{array}$

(c)

Interpretation Introduction

Interpretation: The two repeating units of ABS plastic assuming the three monomer units react in a $1:1:1$ mole ratio and in the same order as the monomers are to be drawn. The percent by mass of acrylonitrile, butadiene and styrene in the polymer sample is to be calculated and the relative numbers of monomer units in the given sample of ABS plastic is to be determined.

Concept introduction: The polymers (repeating structural units) are derived from the simple and reactive molecules, called as monomers. ABS plastic is a terpolymer of styrene, acrylonitrile and polybutadiene.

To determine: The relative numbers of monomer units in the given sample of ABS plastic.

Answer to Problem 168CP

Answer

The three monomer units are in $1:1:2$ molar ratios respectively.

Explanation of Solution

Explanation

The relative numbers of the monomer unit in ABS sample is explained below.

On the basis of the above results it is considered that the three monomer unit’s; acrylonitrile, butadiene and styrene are present in $1:1:2$ molar ratios respectively.