Q.Sucrose (cane sugar) is a disaccharide. One molecule of sucrose on hydrolysis gives _______.

The key idea is that sucrose is a disaccharide composed of one glucose unit and one fructose unit linked by an $\alpha$‑1,2‑glycosidic bond. Hydrolysis breaks this bond.

1. Sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$) + $\text{H}_2\text{O}$ $\xrightarrow{\text{acid or invertase}}$ glucose + fructose.
2. The products are one molecule of D‑glucose and one molecule of D‑fructose — not two of the same monosaccharide.

The key to this question is knowing the composition of sucrose. Many students memorise that maltose gives two glucoses, and lactose gives glucose + galactose, but sucrose is different. It’s the common table sugar, and its structure is $\alpha$-D-glucopyranosyl-(1→2)-$\beta$-D-fructofuranoside. That mouthful simply means: one glucose ring linked to one fructose ring via their anomeric carbons.

When you hydrolyse sucrose — with dilute acid or the enzyme invertase — that glycosidic bond breaks. Water adds across the bond, and you get the two free monosaccharides.

1. Identify the monomers. Sucrose is not made of two identical units. It’s a heterodisaccharide: one glucose and one fructose.
2. What does hydrolysis do? Hydrolysis cleaves the bond between the two sugars. Each monomer gets an –OH and an –H from water, restoring their individual ring structures.
3. Count the products. One sucrose molecule → one glucose + one fructose. No extra molecules appear.

Concept: Hydrolysis of Disaccharides

Method: Structural Recall of Sucrose Composition

Steps:

1. Recall the structure of sucrose

   Sucrose is a disaccharide composed of one glucose unit and one fructose unit linked by an $\alpha$‑1,2‑glycosidic bond.

2. Understand hydrolysis

   Hydrolysis breaks the glycosidic bond by adding a water molecule ($H_2O$), releasing the two monosaccharide units.

3. Write the reaction

4. Count the products The products are 1 molecule of glucose and 1 molecule of fructose.

Final Answer:

(C) 1 molecule of glucose + 1 molecule of fructose

Common Mistakes on Sucrose Hydrolysis

The Correct Answer

The correct answer is (C) 1 molecule of glucose + 1 molecule of fructose.

Sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$) on hydrolysis yields:

Mistake #1: Thinking sucrose gives two glucose molecules

Why students make this mistake:

They confuse sucrose with maltose (which is glucose + glucose) or cellobiose (also glucose + glucose). Many students memorise "disaccharide → two monosaccharides" and assume both are the same.

How to avoid:

• Memorise the specific composition of each common disaccharide:
  • Sucrose = glucose + fructose
  • Maltose = glucose + glucose
  • Lactose = glucose + galactose
• Draw the structures once — seeing the different rings (glucose has an aldehyde group, fructose has a ketone group) helps fix the pairing.

Mistake #2: Choosing two glucose + one fructose (option B)

Why students make this mistake:

They think "disaccharide" means two sugars, but then add an extra monosaccharide by mistake — often because they recall that sucrose is made from glucose and fructose, but then think hydrolysis adds something.

How to avoid:

• Remember: hydrolysis breaks one bond → one water molecule adds → two monosaccharides result.
• A disaccharide has exactly two monosaccharide units. Hydrolysis cannot produce three sugars.
• Use the formula check: $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + \text{C}_6\text{H}_{12}\text{O}_6$ Two molecules of $\text{C}_6\text{H}_{12}\text{O}_6$ — but they are different isomers (glucose and fructose).

Mistake #3: Choosing two fructose molecules (option D)

Why students make this mistake:

They remember that sucrose is "invert sugar" and that fructose is sweeter, so they assume both products are fructose.

How to avoid:

• Learn the glycosidic bond in sucrose: it is $\alpha$-(1→2) between glucose and fructose.
• The bond involves the anomeric carbon of both — so the products are one glucose and one fructose, not two of the same.
• Remember the invert sugar fact: it is an equimolar mixture of glucose and fructose — not pure fructose.

Quick Memory Aid

Final tip: In exam questions, if you see "cane sugar" or "table sugar", immediately think glucose + fructose — never anything else.