Will the following carbohydrates produce a positive Benedict’s test?
(b) lactose

Verified step by step guidance

1. Understand that Benedict's test is used to identify reducing sugars, which have free aldehyde or ketone groups capable of reducing copper(II) ions to copper(I) oxide, resulting in a color change.
2. Recognize that lactose is a disaccharide composed of glucose and galactose linked by a β(1→4) glycosidic bond.
3. Determine if lactose has a free anomeric carbon that can open to form an aldehyde group, which is necessary for a positive Benedict's test.
4. Recall that in lactose, the glucose unit has a free anomeric carbon, allowing it to act as a reducing sugar.
5. Conclude that since lactose has a free anomeric carbon, it will produce a positive Benedict's test, indicating it is a reducing sugar.

Key Concepts

Benedict's Test

Benedict's test is a qualitative assay used to detect reducing sugars in a solution. When a reducing sugar is present, the copper(II) ions in the Benedict's reagent are reduced to copper(I) oxide, resulting in a color change that can range from green to brick red, depending on the amount of sugar present. This test is commonly used in biochemistry to identify sugars like glucose and lactose.

Reducing Sugars

Reducing sugars are carbohydrates that can donate electrons to other molecules, thus reducing them. This property is due to the presence of a free aldehyde or ketone group in their structure. Common examples include glucose, fructose, and lactose, which can all participate in redox reactions, making them detectable by tests like Benedict's.

Lactose

Lactose is a disaccharide sugar composed of glucose and galactose, commonly found in milk. It is classified as a reducing sugar because it has a free aldehyde group when in solution, allowing it to react with Benedict's reagent. Therefore, lactose will produce a positive result in a Benedict's test, indicating the presence of reducing sugars.