You are given a 5 mM solution of sucrose. If you hydrolyse it by adding equal volume of 10
Mm HCl, what would be the final concentration of glucose and fructose in the hydrolysate?
A. 5 mM glucose and 5 mM fructose
B. 2.5 mM glucose and 2.5 mM fructose
C. 1.25 mM glucose and 1.25 mM fructose
D. 1.25 mM glucose and 2.5 mM fructose

Hydrolysing Sucrose with HCl: Final Sugar Concentrations Explained

Introduction

Hydrolysis reactions are essential in biochemistry, especially when breaking down complex sugars. A common question in exams and interviews is:

You are given a 5 mM solution of sucrose. If you hydrolyze it by adding equal volume of 10 mM HCl, what would be the final concentration of glucose and fructose in the hydrolysate?

Let’s walk through the concept step-by-step and determine the right answer.

Step 1: Understand the Reaction

Sucrose is a disaccharide composed of glucose and fructose. When hydrolyzed (with acid like HCl), it breaks down into its two monosaccharide components:

            sucrose+H2O→glucose+fructose                

So, 1 mole of sucrose gives 1 mole of glucose and 1 mole of fructose.

Step 2: Consider Dilution from Mixing

You have:

• 5 mM sucrose solution (initial volume V)
• Equal volume of 10 mM HCl added (volume V)

After mixing, the total volume doubles. This means the concentration of sucrose becomes:

                                          5 mM/2   

                                        =2.5 mM

Step 3: Hydrolysis Conversion

Assuming complete hydrolysis, the entire 2.5 mM sucrose gets converted to:

• 2.5 mM glucose
• 2.5 mM fructose

✅ Correct Answer: B. 2.5 mM glucose and 2.5 mM fructose

Why HCl is Used

Hydrochloric acid (HCl) provides the acidic condition needed to catalyze the hydrolysis of sucrose. The higher the HCl concentration, the faster the reaction proceeds.

Conclusion

When a 5 mM sucrose solution is hydrolyzed by mixing with an equal volume of 10 mM HCl, the sucrose concentration is halved due to dilution. Upon complete hydrolysis, the final concentrations are:

• 2.5 mM glucose
• 2.5 mM fructose

This type of question tests your grasp of dilution, reaction stoichiometry, and basic carbohydrate chemistry.

Always account for volume changes when mixing solutions before calculating final concentrations!