Question

Why is cellulose insoluble in water?

Short answer

Answer: Cellulose is insoluble in water due to its extensive network of strong hydrogen bonds between its linear chains. These hydrogen bonds within cellulose are much stronger than the hydrogen bonds formed between water molecules. As a result, water molecules cannot effectively break the hydrogen bonds between cellulose chains, preventing cellulose from dissolving in water.

Step-by-step solution

Understand the structure of cellulose

Cellulose is a long-chain polysaccharide, consisting of β-D-glucose monomers linked together by β(1→4) glycosidic bonds. These β(1→4) glycosidic bonds create a linear, unbranched structure, which allows the cellulose chains to lie closely together and form strong hydrogen bonds between adjacent chains.

Define solubility and the role of hydrogen bonding

Solubility is the ability of a solute to dissolve in a solvent, and it is largely dependent on the strength and type of molecular interactions occurring between solute and solvent molecules. In order for a substance to dissolve in water, it must form hydrogen bonds with the water molecules. These new hydrogen bonds between solute and solvent must be of comparable or stronger strength than the bonds within the solute and within the solvent for the substance to dissolve.

Compare hydrogen bonding in cellulose and water

Water molecules are able to form hydrogen bonds with each other because of the polarity of the O-H bonds in water. These hydrogen bonds keep the water molecules together and promote solubility of polar substances. In cellulose, the hydrogen bonds are formed between the hydroxyl groups (-OH) of adjacent cellulose chains. The extensive hydrogen bonding between cellulose chains results in the formation of a sturdy, three-dimensional network.

Explain why cellulose is insoluble in water

The reason why cellulose is insoluble in water is due to the extensive network of hydrogen bonds formed between the cellulose chains. These hydrogen bonds are much stronger than the hydrogen bonds formed between water molecules. When water molecules try to interact with cellulose, they are not able to compete with the strength of the hydrogen bonds within cellulose, thus cannot effectively break the hydrogen bonds between cellulose chains. As a consequence, cellulose remains insoluble in water.