Problem 69 - Chemistry: The Central Science

Question

(a) What is the empirical formula of cellulose? (b) What is the monomer that forms the basis of the cellulose polymer? (c) What bond connects the monomer units in cellulose: amide, acid, ether, ester, or alcohol?

Step-by-Step Solution

Answer

(a) The empirical formula of cellulose is \(C_6H_{10}O_5\). (b) The monomer that forms the basis of the cellulose polymer is the glucose molecule, specifically beta-glucose. (c) The bond that connects the monomer units in cellulose is an ether bond.

Step 1: (a) Determine the empirical formula of cellulose

(Cellulose is a complex carbohydrate with the molecular formula \(C_6H_{10}O_5\). In order to find the empirical formula, we need to simplify this formula to its lowest terms. Divide the ratios of the elements by their greatest common divisor, which in this case is 1. Therefore, the empirical formula of cellulose is the same as its molecular formula: \(C_6H_{10}O_5\).)

Step 2: (b) Identify the monomer of cellulose

(Cellulose is a polymer composed of repeated monomer units. The monomer that forms the basis of the cellulose polymer is the glucose molecule. Specifically, cellulose is made up of beta-glucose units, which have the molecular formula \(C_6H_{12}O_6\).)

Step 3: (c) Determine the bond connecting the monomer units in cellulose

(To identify the bond connecting monomer units in cellulose, we need to examine how glucose molecules are linked together. In cellulose, glucose molecules are joined by beta-1,4-glycosidic linkages. These linkages involve the formation of ether bonds between the hydroxyl groups (-OH) of adjacent glucose molecules. Therefore, the bond that connects monomer units in cellulose is an ether bond.)

Key Concepts

Empirical Formula

The empirical formula is the simplest integer ratio of the atoms within a compound. It's a representation of the proportions of each element in a molecule, without showing the actual numbers of atoms in the molecule.

In the context of cellulose, a complex carbohydrate, understanding its empirical formula is vital to grasping the basic structural unit of this abundant natural polymer. An empirical formula is derived by reducing the molecular formula to its simplest whole number ratio. For cellulose, given the molecular formula as \(C_6H_{10}O_5\), the greatest common divisor of the subscripts is 1. Therefore, the empirical formula for cellulose remains \(C_6H_{10}O_5\), indicating that for every six carbon atoms, there are ten hydrogen atoms and five oxygen atoms in the simplest ratio defining this substance's composition.

Being able to determine the empirical formula is a foundational skill in chemistry which facilitates the understanding of more complex structures and reactions involving the compound in question.

Polymer Chemistry

Polymer chemistry is a branch of chemistry that focuses on the study of polymers, large molecules composed of repeating structural units known as monomers. These monomers can join together in various ways to create diverse materials with unique properties.

Cellulose is a prime example of a natural polymer. In nature, it is the primary structural component of plant cell walls and is essential for maintaining the rigidity and strength of the plant structure. The monomer unit for the cellulose polymer is glucose, a simple sugar with the formula \(C_6H_{12}O_6\). Through a dehydration reaction, these glucose molecules link together to form the long chains characteristic of cellulose.

Understanding the polymerization process, in which monomers like glucose connect end to end, helps us to understand the development of the complex structure of cellulose and its properties such as insolubility in water, high tensile strength, and resistance to many chemicals.

Glycosidic Linkage

Glycosidic linkage is the type of covalent bond that connects two sugar molecules, including within polysaccharides like cellulose. This bond is crucial for the structure and stability of carbohydrate polymers.

In cellulose, each glucose monomer is linked to the next through a specific type of glycosidic bond known as the beta-1,4-glycosidic linkage. This bond forms when a hydroxyl group (\(-OH\)) of one glucose molecule reacts with another, releasing a molecule of water (\(H_2O\)) and creating an ether bond.

The orientation of the glucose units and the type of glycosidic bond greatly influence the properties of cellulose. The beta-1,4-glycosidic linkages in cellulose give it a straight, rigid structure that allows it to form strong fibrous materials. Understanding these linkages provides insight into how the structure of cellulose contributes to its function in nature as well as its utilization in human-made materials.