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Mobile App Chapter 19: Problem 82
(a) Draw a structural formula showing the polymer that can be formed from the following monomers (show four units): (1) propylene, (2) 1-butene, (3) 2-butene. (b) How many ethylene units are in a polyethylene molecule that has a molar mass of 35,000 ?
Short Answer
Expert verified
Polymers: ...-CH2-CH(CH3)-..., ...-CH2-CH(CH2-CH3)-..., ...-CH3-CH-...; 1250 ethylene units.
Step by step solution
01
Understand monomers
Identify the structural formulas of the given monomers: propylene, 1-butene, and 2-butene.
02
Structural formula of propylene
The structure of propylene (C3H6) is: CH2=CH-CH3
03
Structural formula of 1-butene
The structure of 1-butene (C4H8) is: CH2=CH-CH2-CH3
04
Structural formula of 2-butene
The structure of 2-butene (C4H8) is: CH3-CH=CH-CH3
05
Polymer from propylene
Propylene polymerizes to form poly(propylene), which has the structure: ...-CH2-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-...
06
Polymer from 1-butene
1-butene polymerizes to form poly(1-butene), which has the structure: ...-CH2-CH(CH2-CH3)-CH2-CH(CH2-CH3)-CH2-CH(CH2-CH3)-CH2-CH(CH2-CH3)-...
07
Polymer from 2-butene
2-butene polymerizes to form poly(2-butene), which has the structure: ...-CH3-CH-CH(CH3)-CH3-CH-CH(CH3)-CH3-CH-CH(CH3)-CH3-CH-CH(CH3)-...
08
Molar mass of ethylene
Each ethylene unit (CH2=CH2) in polyethylene has a molar mass of 28 g/mol (2 carbon atoms at 12 g/mol each and 4 hydrogen atoms at 1 g/mol each).
09
Calculate number of ethylene units
The number of ethylene units in a polyethylene molecule with a molar mass of 35,000 g/mol is found by dividing the total molar mass by the molar mass of one ethylene unit: Number of units = 35000 g/mol / 28 g/mol = 1250
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Monomers
Monomers are the building blocks of polymers. They are small, simple molecules that can join together to form long chains, called polymers. Imagine monomers as individual LEGO bricks. When you snap them together, you create a larger structure. Monomers have specific structures and chemical properties that allow them to bond with other monomers. Common monomers include ethylene, propylene, and butene. Each type of monomer forms a different polymer with unique properties.
Structural Formula
The structural formula of a monomer shows the arrangement of atoms and bonds within the molecule. It's like a blueprint that tells us how the atoms are connected. For example, the structural formula for propylene (C3H6) is CH2=CH-CH3. This tells us that propylene has a double bond between two carbon atoms and a single bond connecting the third carbon atom. Similarly, 1-butene (C4H8) has the structure CH2=CH-CH2-CH3, where the double bond is at the first carbon, while 2-butene (C4H8) has CH3-CH=CH-CH3, indicating the double bond is between the second and third carbon. These blueprints are critical for understanding how monomers connect to form polymers.
Molar Mass
Molar mass is the mass of one mole of a substance, usually measured in grams per mole (g/mol). It helps us understand how heavy a molecule is by summing the masses of all its atoms. In the context of polymers, knowing the molar mass of the repeating unit (monomer) helps calculate the mass of the entire polymer. For instance, the molar mass of an ethylene unit (CH2=CH2) is 28 g/mol, calculated as (2 carbons x 12 g/mol) + (4 hydrogens x 1 g/mol). To find how many ethylene units make up a polyethylene molecule of molar mass 35,000 g/mol, we divide the total mass by the mass of one unit: 35,000 g/mol ÷ 28 g/mol = 1250 units.
Ethylene Units
Ethylene units are the simplest building blocks in polyethylene, a common plastic. Each ethylene unit is composed of two carbon atoms and four hydrogen atoms, symbolized as CH2=CH2. When these units polymerize, they form long chains. The process usually involves breaking the double bond and linking multiple ethylene units in a head-to-tail fashion: ...-CH2-CH2-CH2-CH2-... The length of these chains can vary, but they typically consist of thousands of ethylene units. This chain formation and the length of the polymer determine the properties, such as strength and flexibility, of the resulting polyethylene material.
Polymer Types
Polymers come in a variety of types based on the monomers they are composed of and their structural arrangements. Some common polymers include poly(propylene), poly(1-butene), and poly(2-butene). For example:
- Poly(propylene): Formed from the monomer propylene (CH2=CH-CH3), it has the repeated unit ...-CH2-CH(CH3)-...
- Poly(1-butene): Created from 1-butene (CH2=CH-CH2-CH3), its repeating unit is ...-CH2-CH(CH2-CH3)-...
- Poly(2-butene): Derived from 2-butene (CH3-CH=CH-CH3), its unit is ...-CH3-CH-CH(CH3)-...
