Carbohydrates

(a) Glucose + HI → n-hexane
(b) Glucose + Br₂ water → gluconic acid

(a) Br₂ water
When D-glucose is treated with bromine water (Br₂ in H₂O), the aldehyde (-CHO) group at C-1 is selectively oxidized to a carboxylic acid (-COOH), forming D-gluconic acid.

(b) HCN
When D-glucose is treated with hydrogen cyanide (HCN), the -CHO (aldehyde) group at C-1 reacts with HCN, forming a cyanohydrin (-C(OH)(CN)). This reaction increases the carbon chain by one, leading to the formation of a cyanohydrin derivative.

Monosaccharides, Disaccharides, and Polysaccharides

A disaccharide is a carbohydrate composed of two monosaccharide units joined by a glycosidic bond. Let's explore the components involved in this category.

Monosaccharides:

• Glucose is a monosaccharide, a simple sugar that serves as a primary source of energy for the body.
• Fructose is another monosaccharide, often found in fruits and honey.

Disaccharides:

• Lactose is a disaccharide made up of two monosaccharide units: glucose and galactose. It is commonly found in milk and is the sugar that gives milk its sweetness.

Polysaccharides:

• Amylose is a polysaccharide made up of long chains of glucose units. It is a component of starch, which is a storage form of glucose in plants.

Conclusion:

- Glucose and fructose are monosaccharides, meaning they are single sugar units. - Lactose is a disaccharide composed of two monosaccharides: glucose and galactose. - Amylose is a polysaccharide made up of multiple glucose units.

Summary:

Thus, out of the given options, lactose is the disaccharide, formed by the glycosidic bond between glucose and galactose.

The question asks which statement about glucose is not true. Let's evaluate each option:

• Glucose is an aldose: Glucose is indeed an aldose, as it contains an aldehyde group at the first carbon. Hence, this statement is true.
• On heating with HI, glucose forms n-hexane: This is a characteristic reaction where the entire glucose molecule reduces to n-hexane when treated with hydrogen iodide. Thus, this statement is also true.
• It exists in furanose form: Glucose typically forms a pyranose ring when cyclized, not a furanose form. Therefore, this statement is not true about glucose.
• It does not give Schiff's test: Glucose does not give a positive Schiff's test because while it contains an aldehyde group, it forms a stable cyclic hemiacetal form that typically doesn't react with Schiff's reagent. Hence, this statement is true.

Considering the analysis above, the statement that is not true about glucose is: It exists in furanose form.