Neutralization Reactions, the pH Scale and Properties of Salts for SS 1

Class: SS 1
Term: Third Term
Week: 4
Age: 15 years
Duration: 60 minutes
Subject: Chemistry
Curriculum Theme: The chemical world
Focal competence: Identifying acids, bases and salts in substances
Key competencies/values: Critical Thinking; Communication
Skills:

• Measuring acidity and alkalinity using pH meter
• Preparing types of salts

Previous Lesson: Meanings of acids, bases and salts
Topic: Acids, Bases And Salts: Neutralization Reaction
Subject Matter: Neutralization reaction, Relative acidity and alkalinity (the pH scale) Properties of salts

Specific Objectives

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

Cognitive Domain

• Write balanced equations for neutralization reactions.
• Describe the pH scale.
• Discuss the importance of pH values in various contexts.
• Identify normal, acidic, and basic salts.

Affective Domain

• Appreciate the critical thinking involved in understanding chemical reactions.
• Communicate effectively about chemical concepts.

Psychomotor Domain

• Demonstrate the ability to measure acidity and alkalinity (e.g., using a pH meter if available).
• Outline the steps for preparing different types of salts.

Social Domain

• Collaborate in discussions about the properties of substances.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• Essential Chemistry for Senior Secondary Schools by O. Y. Ababio
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts showing the pH scale with examples of common substances
• Samples of ripe and unripe fruits
• Sour milk
• Flowers and leaves of plants (for natural indicators, if applicable)
• Chemicals: Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH), Hydrochloric Acid (HCl), Sulphuric Acid (H₂SO₄)
• Distilled water
• Test tubes and racks
• Beakers
• Droppers
• pH paper or universal indicator solution (if pH meter is unavailable)

Rationale for the Lesson

This lesson is important for understanding fundamental chemical reactions and the properties of common substances. It provides a basis for comprehending how acids and bases interact and how the pH of a solution affects various biological, industrial, and environmental processes. Knowledge of salts and their properties is essential for practical applications in daily life and further studies in chemistry.

Prerequisite/Previous Knowledge

Students should have basic knowledge of acids and bases, including their definitions and general properties, from previous lessons.

Lesson Content/Board Summary

Neutralization Reaction, The pH Scale and Properties of Salts

Neutralization Reaction

A neutralization reaction is a chemical reaction between an acid and a base (or alkali) that produces a salt and water. In this reaction, the hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH⁻) from the base to form water (H₂O), while the remaining ions form the salt.

General Equation:

Acid + Base → Salt + Water

Examples:

1. Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

[ text{HCl(aq)} + text{NaOH(aq)} rightarrow text{NaCl(aq)} + text{H}_2text{O(l)} ]

2. Sulphuric acid + Potassium hydroxide → Potassium sulphate + Water

[ text{H}_2text{SO}_4text{(aq)} + 2text{KOH(aq)} rightarrow text{K}_2text{SO}_4text{(aq)} + 2text{H}_2text{O(l)} ]

The pH Scale

The pH scale is a numerical scale used to specify the acidity or alkalinity (basicity) of an aqueous solution. It ranges from 0 to 14.

1. pH < 7: Indicates an acidic solution. The lower the pH value, the stronger the acid.
2. pH = 7: Indicates a neutral solution.
3. pH > 7: Indicates an alkaline (basic) solution. The higher the pH value, the stronger the base.

Examples of pH values for common substances:

1. Battery acid: ~0
2. Lemon juice: ~2
3. Vinegar: ~2.5
4. Orange juice: ~3.5
5. Coffee: ~5
6. Milk: ~6.5
7. Pure water: 7 (neutral)
8. Blood: ~7.4
9. Baking soda solution: ~8.5
10. Ammonia solution: ~11
11. Bleach: ~12.5
12. Drain cleaner: ~14

Importance of pH Values

The pH value is very important in various aspects of life and industry:

1. Agriculture: Soil pH affects nutrient availability and crop growth. Different crops thrive at specific pH ranges.
2. Biology and Medicine: Human blood pH is strictly maintained between 7.35 and 7.45 for proper body function. Enzymes in the body also function optimally at specific pH values.
3. Food Industry: pH is critical in food preservation, fermentation, and quality control (e.g., in dairy products, soft drinks).
4. Water Treatment: pH adjustment is necessary for effective coagulation, disinfection, and corrosion control in water purification.
5. Environmental Monitoring: The pH of rivers and lakes indicates pollution levels, especially acid rain effects.
6. Everyday Products: Many personal care products like shampoos and soaps are formulated to be pH-balanced for skin and hair health.

Types of Salts

Salts can be classified into normal, acidic, and basic salts based on their composition and the extent of neutralization.

Normal Salts

These are formed by the complete replacement of all ionizable hydrogen atoms of an acid by a metal or ammonium ion. They do not contain replaceable hydrogen atoms or hydroxyl groups.

Examples:

1. Sodium chloride (NaCl)
2. Potassium sulphate (K₂SO₄)
3. Calcium nitrate (Ca(NO₃)₂)

Preparation Example:

[ text{HCl(aq)} + text{NaOH(aq)} rightarrow text{NaCl(aq)} + text{H}_2text{O(l)} ]

Acidic Salts

These are formed by the incomplete replacement of ionizable hydrogen atoms of a polybasic acid (an acid with more than one replaceable hydrogen atom) by a metal or ammonium ion. They still contain replaceable hydrogen atoms.

Examples:

1. Sodium hydrogen sulphate (NaHSO₄) from sulphuric acid
2. Sodium hydrogen carbonate (NaHCO₃) from carbonic acid
3. Potassium dihydrogen phosphate (KH₂PO₄) from phosphoric acid

Preparation Example:

[ text{H}_2text{SO}_4text{(aq)} + text{NaOH(aq)} rightarrow text{NaHSO}_4text{(aq)} + text{H}_2text{O(l)} ]

Basic Salts

These are formed by the incomplete replacement of hydroxyl groups (OH⁻) of a polyacidic base (a base with more than one hydroxyl group) by an acid radical. They still contain replaceable hydroxyl groups.

Examples:

1. Magnesium hydroxide chloride (Mg(OH)Cl)
2. Lead(II) hydroxide nitrate (Pb(OH)NO₃)
3. Zinc hydroxide chloride (Zn(OH)Cl)

Preparation Example:

[ text{Mg(OH)}_2text{(aq)} + text{HCl(aq)} rightarrow text{Mg(OH)Cl(aq)} + text{H}_2text{O(l)} ]

Properties of Salts

Some salts exhibit specific behaviours when exposed to the atmosphere due to their interaction with moisture.

Hygroscopic Substances

These are substances that absorb moisture from the atmosphere without dissolving in it. They simply become damp or sticky.

Examples:

1. Anhydrous calcium chloride (CaCl₂)
2. Silica gel
3. Concentrated sulphuric acid

Deliquescent Substances

These are substances that absorb so much moisture from the atmosphere that they dissolve in the absorbed water to form a solution. This process is called deliquescence.

Examples:

1. Sodium hydroxide (NaOH) pellets
2. Iron(III) chloride (FeCl₃)
3. Magnesium chloride (MgCl₂)

Efflorescent Substances

These are crystalline hydrated salts that lose their water of crystallisation to the atmosphere when exposed, becoming powdery. This process is called efflorescence.

Examples:

1. Sodium carbonate decahydrate (washing soda), Na₂CO₃·10H₂O
2. Copper(II) sulphate pentahydrate (blue vitriol), CuSO₄·5H₂O
3. Glauber’s salt (sodium sulphate decahydrate), Na₂SO₄·10H₂O

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Recalling

Teacher’s Activity: The teacher greets the students and asks them to recall what they learned about acids and bases in the previous lesson, including their general properties.

Pupils’ Activity: Pupils respond by mentioning properties of acids (sour taste, turn blue litmus red) and bases (bitter taste, turn red litmus blue).

Learning Point: Review of acids/bases

Step 2: Neutralization Reaction

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains what a neutralization reaction is, stating that it’s a reaction between an acid and a base to form salt and water. The teacher writes the general equation and provides examples, demonstrating with HCl and NaOH if possible using an indicator to show the neutral point.

Pupils’ Activity: Pupils observe the demonstration, listen to the explanation, and copy the equations into their notebooks.

Learning Point: Acid-base reaction explained

Step 3: The pH Scale

Time: 10 minutes

Teaching Skill: Explanation/Visual Aid

Teacher’s Activity: The teacher introduces the pH scale, explaining its range (0-14) and how it indicates acidity, neutrality, or alkalinity. The teacher uses a chart to show common substances and their pH values and demonstrates with pH paper or universal indicator using various samples (e.g., lemon juice, soap solution, distilled water).

Pupils’ Activity: Pupils observe the chart and demonstration, identify the pH of different substances, and understand the concept of pH values.

Learning Point: pH scale interpretation

Step 4: Importance of pH Values

Time: 5 minutes

Teaching Skill: Discussion/Elaboration

Teacher’s Activity: The teacher leads a discussion on the importance of pH values in everyday life, agriculture, biology, and industry, linking it to the examples provided in the content scope.

Pupils’ Activity: Pupils contribute to the discussion by giving examples of where pH is important, such as soil for farming or blood pH.

Learning Point: Practical pH applications

Step 5: Types of Salts

Time: 10 minutes

Teaching Skill: Explanation/Classification

Teacher’s Activity: The teacher explains the three main types of salts: normal, acidic, and basic salts. For each type, the teacher defines it, provides chemical examples, and explains how they are formed, guiding students to identify and prepare them conceptually.

Pupils’ Activity: Pupils listen, ask questions for clarification, and identify the characteristics of each salt type.

Learning Point: Salt classification explained

Step 6: Properties of Salts

Time: 5 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher discusses the properties of hygroscopic, deliquescent, and efflorescent substances, providing examples for each. The teacher guides students to discuss observable changes when these substances are exposed to air.

Pupils’ Activity: Pupils listen, observe, and discuss the differences in how these substances interact with atmospheric moisture.

Learning Point: Hygroscopic, deliquescent, efflorescent

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. Write a balanced equation for the neutralization of sulphuric acid by potassium hydroxide.
2. Describe the pH scale and state the pH range for acidic, neutral, and alkaline solutions.
3. Give two reasons why understanding pH values is important.
4. Differentiate between a normal salt and an acidic salt with an example for each.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Neutralization, pH, salt properties

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on neutralization reactions, the pH scale, and properties of salts into their notebooks.

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

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarization

Teacher’s Activity: The teacher briefly summarizes the key concepts of neutralization, the pH scale, and the different types and properties of salts, reinforcing their importance in chemistry and daily life. The teacher addresses any remaining questions.

Pupils’ Activity: Pupils listen attentively and ask final questions.

Learning Point: Lesson concepts consolidated

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Answer the following questions in your notebook.

1. Define neutralization reaction and give two examples of strong acid-strong base neutralization.
2. Explain what the pH scale measures. Provide the approximate pH values for pure water, stomach acid, and household ammonia.
3. Discuss three practical applications where knowing the pH value is crucial.
4. Classify the following salts as normal, acidic, or basic: NaNO₃, NaH₂PO₄, Zn(OH)NO₃.
5. Describe the difference between hygroscopic and deliquescent substances, giving one example for each.

Lesson Keywords

• Neutralization – A chemical reaction between an acid and a base, producing a salt and water.
• pH Scale – A scale from 0 to 14 indicating the acidity or alkalinity of a solution.
• Acidic Solution – A solution with a pH value less than 7.
• Alkaline Solution – A solution with a pH value greater than 7.
• Neutral Solution – A solution with a pH value of 7.
• Normal Salt – A salt formed by complete replacement of acidic hydrogen atoms.
• Acidic Salt – A salt formed by incomplete replacement of acidic hydrogen atoms.
• Basic Salt – A salt formed by incomplete replacement of basic hydroxyl groups.
• Hygroscopic – Absorbing moisture from the air without dissolving.
• Deliquescent – Absorbing enough moisture from the air to dissolve and form a solution.
• Efflorescent – Losing water of crystallisation to the atmosphere.

Differentiation

For students who may struggle, provide simplified examples of neutralization reactions and use visual aids extensively for the pH scale. Encourage peer tutoring. For advanced learners, challenge them to research more complex neutralization reactions or investigate the pH of various local environmental samples (e.g., rainwater, soil samples) and discuss their implications.

Suggested Lesson Videos

Search on YouTube for: neutralization reaction pH scale salts SS1 chemistry