Problem 70 - Chemistry: The Central Science

Question

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

Step-by-Step Solution

Answer

(a) The empirical formula of starch is C6H12O6, as it is composed of glucose units. (b) The monomer that forms the basis of the starch polymer is glucose. (c) The bond connecting the monomer units in starch is an alpha-1,4-glycosidic bond, which is a type of ether bond.

Step 1: (a) Empirical formula of starch

Starch is a carbohydrate polymer made up of glucose monomer units. The empirical formula of glucose is C6H12O6. Since starch is composed entirely of glucose units, its empirical formula is also C6H12O6.

Step 2: (b) Monomer that forms the basis of the starch polymer

The monomer that forms the basis of the starch polymer is glucose. Glucose is a simple sugar with the molecular formula C6H12O6.

Step 3: (c) Type of bond that connects the monomer units in starch

The type of bond that connects the monomer units in starch is a glycosidic bond. Specifically, it is an alpha-1,4-glycosidic bond. This bond is a type of ether bond, formed between hydroxyl groups of two glucose monomers through a dehydration synthesis reaction, which means an ether bond connects the monomer units in starch.

Key Concepts

Empirical Formula of Starch

The empirical formula is the simplest whole-number ratio of atoms in a compound. For starch, which is composed entirely of glucose monomers, it's significant because it mirrors the glucose units themselves.
Glucose, a simple sugar, has the molecular formula C_6H_{12}O_6. However, when it comes to complex carbohydrates like starch, the empirical formula highlights the base unit that repeats.
Starch itself is a polymer where each glucose unit is linked together. Even though the entire polymer is extensive, the empirical formula remains the same as glucose: C_6H_{12}O_6. This shows the consistent nature of glucose as a building block within starch.

Glucose in Starch

Glucose plays a fundamental role in creating starch, acting as the monomeric unit.
Monomers are the single units that bond together to form polymers, like how beads come together to form a necklace.
In the case of starch, glucose is this bead. It has a molecular formula of C_6H_{12}O_6, making it a hexose sugar due to its six carbon atoms.

• Glucose is crucial as it provides energy and structural integrity with its stable carbon backbone.
• This simple sugar is the most common monosaccharide in many biological structures.

By understanding glucose, you grasp the fundamental sugar that constructs more complex carbohydrates like starch.

Glycosidic Bond Formation

Understanding how glucose units connect in starch involves examining the glycosidic bond.
These bonds act as the glue holding each glucose monomer together. Specifically, in starch, the connection is called an alpha-1,4-glycosidic bond.

• An alpha-1,4 glycosidic bond forms when the hydroxyl group on the first carbon of one glucose molecule bonds to the hydroxyl group on the fourth carbon of another glucose molecule.
• This bond is classified as an ether bond, created through a dehydration synthesis process where a water molecule is removed during formation.

This bonding pattern is crucial because it determines the physical properties and digestibility of starch, influencing how it is utilized in biological systems.