Hydrolysis of Sucrose and Starch for SS 3

Class: SS 3
Term: First Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Topic: GIANT MOLECULES
Subject Matter: Hydrolysis of sucrose and starch

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Define hydrolysis in the context of carbohydrates.
• State the conditions required for the hydrolysis of sucrose and starch.
• Identify the products formed from the hydrolysis of sucrose and starch.
• Explain the chemical equations for the hydrolysis of sucrose and starch.

Affective Domain

• Appreciate the importance of hydrolysis in biological and industrial processes.
• Observe the experimental demonstration of hydrolysis with keen interest.

Psychomotor Domain

• Demonstrate the simple hydrolysis of sucrose and starch in a laboratory setting.
• Test for the presence of reducing sugars after hydrolysis.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Essential Chemistry for Senior Secondary Schools by O. S. Adebayo and others
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Sucrose solution
• Starch solution
• Dilute hydrochloric acid
• Benedict’s solution
• Iodine solution
• Test tubes and test tube rack
• Bunsen burner or spirit lamp
• Beakers
• Water bath
• Droppers
• Safety goggles

Rationale for the Lesson

This lesson is important as it provides students with a foundational understanding of carbohydrate breakdown, a process central to digestion and industrial applications. Understanding hydrolysis helps students grasp how complex sugars are converted into simpler forms, which is crucial for metabolism and various chemical industries.

Prerequisite/Previous Knowledge

Students should have prior knowledge of carbohydrates, including their classification (monosaccharides, disaccharides, polysaccharides), and basic chemical reactions involving acids and heat.

Lesson Content/Board Summary

GIANT MOLECULES

Hydrolysis of Sucrose

Hydrolysis is a chemical reaction in which a compound reacts with water, causing the breaking of a bond in the compound and the addition of a hydrogen atom and a hydroxyl group to the fragments. For carbohydrates, it involves the breakdown of complex sugars into simpler ones in the presence of water, usually with an acid catalyst and heat.

Sucrose is a disaccharide (non-reducing sugar) composed of one glucose unit and one fructose unit. Its hydrolysis breaks the glycosidic bond, yielding these two monosaccharides.

Conditions for hydrolysis of sucrose:

1. Presence of dilute acid (e.g., HCl or H₂SO₄).
2. Heating.

Equation for hydrolysis of sucrose:

( text{C}_{12}text{H}_{22}text{O}_{11(aq)} + text{H}_2text{O}_{(l)} xrightarrow{text{dilute acid, heat}} text{C}_6text{H}_{12}text{O}_{6(aq)} + text{C}_6text{H}_{12}text{O}_{6(aq)} )

Where:

1. ( text{C}_{12}text{H}_{22}text{O}_{11} ) = Sucrose
2. ( text{H}_2text{O} ) = Water
3. ( text{C}_6text{H}_{12}text{O}_{6} ) = Glucose
4. ( text{C}_6text{H}_{12}text{O}_{6} ) = Fructose

Both glucose and fructose are reducing sugars.

Hydrolysis of Starch

Starch is a polysaccharide, a complex carbohydrate made up of many glucose units linked together. Its complete hydrolysis breaks down these long chains into individual glucose molecules.

The hydrolysis of starch occurs in stages:

1. Starch is first broken down into dextrins (smaller polysaccharides).
2. Dextrins are further hydrolysed to maltose (a disaccharide).
3. Maltose is finally hydrolysed to glucose (a monosaccharide).

Conditions for hydrolysis of starch:

1. Presence of dilute acid (e.g., HCl or H₂SO₄) or enzymes (e.g., amylase).
2. Heating.

Equation for complete hydrolysis of starch:

( (text{C}_6text{H}_{10}text{O}_5)_n + ntext{H}_2text{O} xrightarrow{text{dilute acid, heat}} ntext{C}_6text{H}_{12}text{O}_6 )

Where:

1. ( (text{C}_6text{H}_{10}text{O}_5)_n ) = Starch
2. ( ntext{H}_2text{O} ) = Water
3. ( ntext{C}_6text{H}_{12}text{O}_6 ) = Glucose

The final product of complete starch hydrolysis is glucose, which is a reducing sugar.

Tests for Hydrolysis Products

1. Test for Starch: Add a few drops of iodine solution. A blue-black colour indicates the presence of starch. As hydrolysis proceeds, the colour will change from blue-black to reddish-brown (dextrins) and finally become colourless (no starch).
2. Test for Reducing Sugars (Glucose, Fructose, Maltose): Add Benedict’s solution to the hydrolysed sample and heat gently in a water bath. A colour change from blue to green, yellow, orange, or brick-red precipitate indicates the presence of reducing sugars.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity.

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Recalling

Teacher’s Activity: The teacher greets the students and asks questions about their previous knowledge of carbohydrates, focusing on disaccharides and polysaccharides. For example, “What are some examples of complex sugars you know?” and “How do plants store energy?”

Pupils’ Activity: Students respond to the questions, recalling information about carbohydrates like starch and sucrose.

Learning Point: Prior carbohydrate knowledge

Step 2: Introduction to Hydrolysis

Time: 7 minutes

Teaching Skill: Explanation/Definition

Teacher’s Activity: The teacher introduces the concept of hydrolysis, explaining it as a chemical reaction involving water to break down larger molecules into smaller ones. The teacher relates it to the breakdown of food in the body.

Pupils’ Activity: Students listen attentively and ask questions for clarification on the definition of hydrolysis.

Learning Point: Meaning of hydrolysis

Step 3: Demonstration of Sucrose Hydrolysis

Time: 10 minutes

Teaching Skill: Demonstration/Observation

Teacher’s Activity: The teacher demonstrates the hydrolysis of sucrose. This involves heating a sucrose solution with dilute hydrochloric acid. Before and after heating, the teacher tests for reducing sugars using Benedict’s solution to show the formation of glucose and fructose.

Pupils’ Activity: Students observe the demonstration carefully, noting the changes in the test for reducing sugars before and after hydrolysis.

Learning Point: Sucrose hydrolysis demonstration

Step 4: Explanation of Sucrose Hydrolysis

Time: 5 minutes

Teaching Skill: Explanation/Equation formulation

Teacher’s Activity: The teacher explains the process observed in the sucrose hydrolysis demonstration, writing the chemical equation on the board and highlighting the products (glucose and fructose) and conditions (acid, heat).

Pupils’ Activity: Students copy the equation and notes into their notebooks and ask questions about the reaction mechanism.

Learning Point: Sucrose hydrolysis equation

Step 5: Demonstration of Starch Hydrolysis

Time: 8 minutes

Teaching Skill: Demonstration/Observation

Teacher’s Activity: The teacher demonstrates the hydrolysis of starch. This involves heating a starch solution with dilute hydrochloric acid. The teacher performs iodine tests at intervals to show the disappearance of starch and then tests for reducing sugars using Benedict’s solution to show the formation of glucose.

Pupils’ Activity: Students observe the colour changes with iodine and Benedict’s solution, noting the progressive breakdown of starch.

Learning Point: Starch hydrolysis demonstration

Step 6: Explanation of Starch Hydrolysis

Time: 5 minutes

Teaching Skill: Explanation/Equation formulation

Teacher’s Activity: The teacher explains the stages of starch hydrolysis (dextrins, maltose, glucose) and writes the overall chemical equation for complete hydrolysis on the board, emphasizing the conditions and final product.

Pupils’ Activity: Students copy the equation and notes on starch hydrolysis, clarifying any doubts about the intermediate products.

Learning Point: Starch hydrolysis equation

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is hydrolysis?
2. Name the products formed when sucrose is hydrolysed.
3. State two conditions necessary for the hydrolysis of starch.
4. How would you test for the presence of glucose after starch hydrolysis?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding hydrolysis concepts

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on the hydrolysis of sucrose and starch, including equations and tests, into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson information

Step 9: Conclusion

Time: 1 minute

Teaching Skill: Reinforcement

Teacher’s Activity: The teacher briefly recaps the main points of the lesson, emphasizing the importance of hydrolysis in breaking down complex carbohydrates into simpler sugars.

Pupils’ Activity: Students listen and prepare for the next lesson.

Learning Point: Hydrolysis concept reinforced

Continuous Assessment/Further Study

Type: Homework/Further Reading

Instruction: Answer the following questions in your notebook. You may also research the industrial applications of carbohydrate hydrolysis.

1. Write the balanced chemical equation for the hydrolysis of sucrose, clearly naming all reactants and products.
2. Describe the expected colour changes when iodine solution is added to starch solution at different stages of its hydrolysis.
3. Explain why sucrose is considered a non-reducing sugar while its hydrolysis products are reducing sugars.
4. Research and list two industrial uses of starch hydrolysis.

Lesson Keywords

• Hydrolysis – A chemical reaction involving water to break down a compound.
• Sucrose – A disaccharide (table sugar) made of glucose and fructose.
• Starch – A polysaccharide, a complex carbohydrate made of many glucose units.
• Glucose – A monosaccharide, a simple sugar, and a reducing sugar.
• Fructose – A monosaccharide, a simple sugar, and a reducing sugar.
• Benedict’s solution – A reagent used to test for reducing sugars.
• Iodine solution – A reagent used to test for starch.
• Reducing sugar – A sugar capable of acting as a reducing agent.

Differentiation

For weaker learners: Provide simplified diagrams of the hydrolysis reactions and pre-prepared test tubes for the demonstrations to minimise errors. Focus on identifying the main products and conditions. Provide a handout with the key equations.

For faster learners: Challenge them to research the role of specific enzymes (e.g., sucrase, amylase) in the biological hydrolysis of these carbohydrates. Encourage them to explore the quantitative aspects of the reactions or other examples of giant molecule hydrolysis.

Suggested Lesson Videos

For further understanding, search on YouTube for: hydrolysis of sucrose and starch chemistry

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure all chemicals (sucrose, starch, dilute HCl, Benedict’s solution, iodine solution) and apparatus (test tubes, Bunsen burner, water bath) are ready and in good working condition. Safety goggles must be worn by both the teacher and students during the practical demonstrations. Start by engaging students with questions about carbohydrates to activate prior knowledge. Clearly explain the concept of hydrolysis before proceeding to the practical demonstrations. During the demonstrations, ensure students can clearly see the colour changes for the Benedict’s and iodine tests. Guide students through the chemical equations for both sucrose and starch hydrolysis, emphasizing the conditions and products. Allow ample time for students to copy the Board Summary notes (Step 8) which include the definitions, equations, and tests. For the “visit to a local sugar” activity mentioned in the seed, this can be planned as a separate educational excursion or assigned as a project for further study, as it extends beyond the scope of a single 45-minute lesson. Continuously check for understanding through questions and provide support to struggling learners while challenging advanced ones with extension tasks.