Problem 67 - Chemistry: The Central Science

Question

Indicate whether each statement is true or false: (a) Disaccharides are a type of carbohydrate. (b) Sucrose is a monosaccharide. (c) All carbohydrates have the formula \(\mathrm{C}_{\mathrm{a}} \mathrm{H}_{2 \mathrm{~m}} \mathrm{O}_{\mathrm{m}}\).

Step-by-Step Solution

Answer

(a) True: Disaccharides are a type of carbohydrate composed of two monosaccharides joined together by a glycosidic bond. (b) False: Sucrose is a disaccharide, not a monosaccharide, as it consists of glucose and fructose joined together. (c) False: The general formula for carbohydrates is \(\mathrm{C}_{\text{n}}(\mathrm{H}_{2 \mathrm{O}})_{\text{n}}\) but not all carbohydrates strictly follow this formula, especially in the case of complex carbohydrates like polysaccharides.

Step 1: Understanding Disaccharides

Disaccharides are a type of carbohydrate that consists of two monosaccharides joined together by a glycosidic bond. Some examples of disaccharides include sucrose, lactose, and maltose.

Step 2: Verifying Statement (a)

Since disaccharides are carbohydrates that consist of two monosaccharides, statement (a) is true. Statement (b): Sucrose is a monosaccharide.

Step 3: Understanding Sucrose

Sucrose is a disaccharide that is composed of two monosaccharides, glucose and fructose, joined together by a glycosidic bond.

Step 4: Verifying Statement (b)

Since sucrose is a disaccharide and not a monosaccharide, statement (b) is false. Statement (c): All carbohydrates have the formula \(\mathrm{C}_{\mathrm{a}} \mathrm{H}_{2 \mathrm{~m}} \mathrm{O}_{\mathrm{m}}\).

Step 5: Understanding Carbohydrate Formula

The general formula for carbohydrates is \(\mathrm{C}_{\text{n}}(\mathrm{H}_{2 \mathrm{O}})_{\text{n}}\), where n is the number of carbon atoms. However, not all carbohydrates strictly follow this formula, as some may have additional functional groups or structural variations, especially in the case of more complex carbohydrates like polysaccharides.

Step 6: Verifying Statement (c)

Since not all carbohydrates follow the formula \(\mathrm{C}_{\mathrm{a}} \mathrm{H}_{2 \mathrm{~m}} \mathrm{O}_{\mathrm{m}}\), statement (c) is false.

Key Concepts

Disaccharides

Disaccharides are an essential type of carbohydrates. They are formed when two monosaccharide molecules link together through a covalent bond, known as a glycosidic bond. This process typically involves a condensation reaction that releases a water molecule. Some common examples of disaccharides include sucrose, lactose, and maltose.

• Sucrose: Found in many plants, commonly known as table sugar, and it's formed from glucose and fructose.
• Lactose: Known as milk sugar, it is composed of glucose and galactose.
• Maltose: Often present in germinating grains, formed by two glucose molecules.

Disaccharides play a crucial role in energy metabolism and are significant components of our diet. They are digested by enzymes into monosaccharides that can be absorbed into the bloodstream.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and are considered the building blocks of more complex sugars like disaccharides and polysaccharides. These simple sugars consist of one sugar unit and can exist in a linear or ring structure. Common examples of monosaccharides include glucose, fructose, and galactose.

• Glucose: Known as blood sugar; it's a primary energy source for cells.
• Fructose: Often found in fruits; it's sweeter than glucose and also used as a key energy source.
• Galactose: Part of milk sugar; similar in structure to glucose but with differences that affect its metabolism.

Monosaccharides are absorbed directly into the bloodstream during digestion, allowing for quick energy release. Their simple structure and quick absorption make them indispensable for various biological processes.

Carbohydrate Formula

The general formula for carbohydrates is often expressed as \[\mathrm{C}_n(\mathrm{H}_{2\mathrm{O}})_n\]. This formula suggests that carbohydrates are essentially hydrates of carbon. This means that for every carbon atom, there is a water molecule. However, not all carbohydrates adhere strictly to this ratio, especially as they become more complex.
Carbohydrates like disaccharides and polysaccharides may have variations from the basic formula due to their structural complexity and additional functional groups. Hence, while the formula is a useful general guide, it's not an absolute rule.
Understanding these variations is important as they can affect the properties and biological functions of carbohydrates, influencing aspects like solubility, digestibility, and energy content.