Meanings of acids, bases and salts for SS 1

Class: SS 1
Term: Third Term
Week: 3
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:

• Testing for acids or bases in fruits and vegetables
• Preparing types of salts

Previous Lesson: Avogadro Number, Mole Concept, Molar Volume and Ideal Gas Equation
Topic: Acids, Bases And Salts
Subject Matter: Meanings of acids, bases and salts, works

Specific Objectives

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

Cognitive Domain

• Define acids, bases and salts.
• Identify acids, bases and salts in various substances.
• State the uses of acids, bases and salts.
• Describe how acid-base indicators work.
• Explain neutralization reaction.
• Mention some common sources of acids and bases.
• Identify different types of salts.

Affective Domain

• Demonstrate critical thinking in classifying substances as acidic or basic.
• Communicate observations and conclusions clearly during practical activities.

Psychomotor Domain

• Test for acids or bases in fruits and vegetables using indicators.
• Illustrate the reactions of acids and bases using chemical reagents.

Social Domain

• Collaborate effectively in group activities involving identification 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
• A suitable Chemistry textbook for SS 1
• 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:

• Litmus paper (red and blue)
• Universal indicator solution and colour chart
• Samples of ripe and unripe fruits (e.g., lemon, lime, orange, unripe mango)
• Sour milk
• Extracts from flowers and leaves of plants (e.g., hibiscus, red cabbage)
• Chemicals: Sodium Hydroxide (NaOH) solution, Potassium Hydroxide (KOH) solution, Hydrochloric Acid (HCl) solution, Sulphuric Acid (H2SO4) solution
• Distilled water
• Test tubes and test tube rack
• Droppers
• Beakers

Rationale for the Lesson

This lesson is important as it introduces students to fundamental chemical concepts that are prevalent in everyday life, from the foods we eat to industrial processes. Understanding acids, bases, and salts provides a foundation for further study in chemistry and helps students appreciate the chemical nature of their environment. It also equips them with practical skills in identifying these substances.

Prerequisite/Previous Knowledge

Students should have basic knowledge of matter, mixtures, and solutions from their Junior Secondary School science classes.

Lesson Content/Board Summary

Acids, Bases And Salts

Meaning of Acids

Acids are substances that produce hydrogen ions (H⁺) when dissolved in water. They typically have a sour taste, are corrosive, and turn blue litmus paper red.

Common sources of acids include:

1. Citrus fruits (e.g., lemons, oranges) contain citric acid.
2. Vinegar contains acetic acid.
3. Sour milk contains lactic acid.
4. Stomach acid is hydrochloric acid (HCl).
5. Car batteries contain sulphuric acid (H₂SO₄).

Characteristics of Acids

1. They have a sour taste (e.g., lemon juice).
2. They are corrosive and can burn skin or damage materials.
3. They turn blue litmus paper red.
4. They react with active metals to produce hydrogen gas.
5. They react with bases to form salt and water (neutralization).
6. They react with carbonates and bicarbonates to produce carbon dioxide gas.

Uses of Acids

1. Hydrochloric acid (HCl) is used in the stomach for digestion and in cleaning metals.
2. Sulphuric acid (H₂SO₄) is used in car batteries, fertilizers, and detergents.
3. Nitric acid (HNO₃) is used in the production of fertilizers and explosives.
4. Acetic acid (CH₃COOH) is used as vinegar in food preservation and flavouring.
5. Citric acid is used as a food additive and preservative in soft drinks and sweets.

Meaning of Bases

Bases are substances that produce hydroxide ions (OH⁻) when dissolved in water. They typically have a bitter taste, feel slippery or soapy, and turn red litmus paper blue.

Common sources of bases include:

1. Soaps and detergents (contain sodium hydroxide or potassium hydroxide).
2. Antacids (contain magnesium hydroxide or aluminium hydroxide).
3. Baking soda (sodium bicarbonate, which is a weak base).
4. Household cleaning agents (e.g., ammonia solution).

Characteristics of Bases

1. They have a bitter taste.
2. They feel soapy or slippery to the touch.
3. They turn red litmus paper blue.
4. They react with acids to form salt and water (neutralization).
5. Strong bases are corrosive.

Uses of Bases

1. Sodium hydroxide (NaOH) is used in making soap, paper, and rayon.
2. Potassium hydroxide (KOH) is used in making liquid soaps and alkaline batteries.
3. Calcium hydroxide (Ca(OH)₂) is used in agriculture to neutralize acidic soil (liming) and in making mortar.
4. Magnesium hydroxide (Mg(OH)₂) is used as an antacid to relieve indigestion.
5. Ammonia (NH₃) solution is used in household cleaners and fertilizers.

Meaning of Salts

Salts are ionic compounds formed when an acid reacts with a base, where the hydrogen ion of the acid is replaced by a metal ion or ammonium ion. They are typically crystalline solids at room temperature.

Types of Salts

Salts can be classified into different types based on their composition or how they are formed:

1. Normal Salts: Formed when all the replaceable hydrogen ions of an acid are completely replaced by a metal or ammonium ion. Examples: NaCl, K₂SO₄.
2. Acid Salts: Formed when only a part of the replaceable hydrogen ions of a polybasic acid is replaced by a metal or ammonium ion. They still contain replaceable hydrogen. Examples: NaHSO₄, NaHCO₃.
3. Basic Salts: Formed when a base reacts with an acid and there is incomplete neutralization, leaving some hydroxide ions in the salt structure. Examples: Mg(OH)Cl, Pb(OH)NO₃.
4. Double Salts: Formed when two simple salts crystallize together from a single solution. Examples: Potash alum (K₂SO₄·Al₂(SO₄)₃·24H₂O).
5. Complex Salts: Contain complex ions, where a central metal atom is bonded to other molecules or ions (ligands). Examples: K₄[Fe(CN)₆].

Uses of Salts

1. Sodium chloride (NaCl) is used as common table salt for seasoning food and as a preservative.
2. Sodium bicarbonate (NaHCO₃) is used as baking soda in baking and as an antacid.
3. Calcium carbonate (CaCO₃) is used in building materials (limestone, marble) and as an antacid.
4. Potassium nitrate (KNO₃) is used in fertilizers and gunpowder.
5. Ammonium sulphate ((NH₄)₂SO₄) is used as a fertilizer.

Acid-Base Indicators

Acid-base indicators are weak organic acids or bases that change colour depending on the pH of the solution they are in. They are used to determine whether a substance is acidic, basic, or neutral.

How Acid-Base Indicators Work

Indicators work by undergoing a reversible colour change as the concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻) in the solution changes. Each indicator has a specific pH range over which it changes colour.

Examples of common indicators and their colour changes:

1. Litmus Paper:
   • In acidic solution: Blue litmus turns red.
   • In basic solution: Red litmus turns blue.
   • In neutral solution: No change.
2. Methyl Orange:
   • In acidic solution (pH < 3.1): Red
   • In basic solution (pH > 4.4): Yellow
3. Phenolphthalein:
   • In acidic solution (pH < 8.2): Colourless
   • In basic solution (pH > 10.0): Pink/Red
4. Universal Indicator: This is a mixture of several indicators that shows a range of colours across the entire pH scale, allowing for a more precise estimation of pH.
   • Strong acid: Red
   • Weak acid: Orange/Yellow
   • Neutral: Green
   • Weak base: Blue
   • Strong base: Violet/Purple

Neutralization Reaction

Neutralization is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water. The general equation for a neutralization reaction is:

Acid + Base → Salt + Water

For example, the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH):

HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

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/Engaging

Teacher’s Activity: The teacher greets the students and asks them to mention some common substances they use daily that taste sour or feel soapy. The teacher then links these properties to acids and bases.

Pupils’ Activity: Pupils respond by mentioning substances like lemon, vinegar, soap, etc.

Learning Point: Everyday acids and bases

Step 2: Meaning and Characteristics of Acids

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher defines acids, explains their characteristics (sour taste, corrosive, turns blue litmus red), and mentions common sources. The teacher demonstrates the effect of an acid (e.g., lemon juice or dilute HCl) on blue litmus paper.

Pupils’ Activity: Pupils listen, observe the demonstration, and ask questions for clarification.

Learning Point: Acid definition and properties

Step 3: Meaning and Characteristics of Bases

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher defines bases, explains their characteristics (bitter taste, soapy feel, turns red litmus blue), and mentions common sources. The teacher demonstrates the effect of a base (e.g., soap solution or dilute NaOH) on red litmus paper.

Pupils’ Activity: Pupils listen, observe the demonstration, and note the differences between acids and bases.

Learning Point: Base definition and properties

Step 4: Acid-Base Indicators and Their Workings

Time: 10 minutes

Teaching Skill: Explanation/Guided Activity

Teacher’s Activity: The teacher explains what acid-base indicators are and how they work, focusing on litmus paper and universal indicator. The teacher guides students to use litmus paper and universal indicator to identify acids and bases in substances like fruit juices (ripe/unripe), sour milk, and plant extracts.

Pupils’ Activity: Pupils actively participate in testing the substances, observing colour changes, and recording their findings.

Learning Point: Indicator function and use

Step 5: Neutralization Reaction

Time: 5 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains the concept of neutralization reaction as the reaction between an acid and a base to form salt and water. The teacher illustrates this using the reaction between HCl and NaOH.

Pupils’ Activity: Pupils listen, observe the chemical equation, and ask questions about the reaction.

Learning Point: Acid-base neutralization

Step 6: Meaning, Types and Uses of Salts

Time: 5 minutes

Teaching Skill: Explanation/Classification

Teacher’s Activity: The teacher defines salts, explains the different types (normal, acid, basic, double, complex salts), and discusses their various uses in daily life and industry.

Pupils’ Activity: Pupils listen and note down the definitions, types, and uses of salts.

Learning Point: Salts: meaning, types, uses

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. Define an acid and a base.
2. How does litmus paper help in identifying an acid or a base?
3. Mention two uses of acids and two uses of bases.
4. What is a neutralization reaction?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Acid-base-salt understanding

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 meanings, characteristics, uses of acids, bases, salts, and how indicators work 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: Summarizing

Teacher’s Activity: The teacher briefly summarises the main points of the lesson, reiterating the definitions and practical applications of acids, bases, and salts in everyday life. The teacher encourages students to observe these substances around them.

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

Learning Point: Consolidated lesson understanding

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your Chemistry notebook.

1. Differentiate between an acid salt and a normal salt, giving one example for each.
2. Describe an experiment you would carry out to determine if a given unknown solution is acidic or basic, stating the materials you would use and the expected observations.
3. List three common household items that are acidic and three that are basic, stating their main acidic or basic component if known.

Lesson Keywords

• Acid – A substance that produces hydrogen ions (H⁺) in water.
• Base – A substance that produces hydroxide ions (OH⁻) in water.
• Salt – An ionic compound formed from the reaction of an acid and a base.
• Indicator – A substance that changes colour in the presence of an acid or a base.
• Neutralization – A reaction between an acid and a base to form salt and water.
• Corrosive – Having the ability to cause damage by chemical action.

Differentiation

For students who grasp concepts quickly, encourage them to research the pH scale and its significance, or investigate the preparation methods for different types of salts. For students needing more support, provide simplified definitions and focus on identifying common acids and bases using litmus paper through repeated practice. Pair stronger students with weaker ones for practical activities.

Suggested Lesson Videos

For further understanding, search on YouTube for:

• Acids, Bases and Salts for SS1 Chemistry
• Acid-Base Indicators Explained