Deliquescent, Efflorescent, Hygroscopic and Solubility of Salts in Water for SS 1

Class: SS 1
Term: Third Term
Week: 5
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:

• Preparing types of salts
• Demonstrating solubility of substances and recording through drawing of apparatus set-up, and making short notes of the activities performed

Previous Lesson: Neutralization Reactions, the pH Scale and Properties of Salts
Topic: Acids, Bases And Salts: Deliquescent, Efflorescent, Hygroscopic
Subject Matter: Deliquescent, Efflorescent, Hygroscopic, Solubility of salts in water

Specific Objectives

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

Cognitive Domain

• Define the terms: hygroscopic, efflorescent, and deliquescent.
• Explain the solubility of salts in water.
• State general properties of salts.
• Distinguish between various applications of pH value.

Affective Domain

• Appreciate the importance of understanding salt properties in everyday life.
• Demonstrate careful handling of chemicals during experiments.

Psychomotor Domain

• Prepare simple salts by neutralization reactions.
• Demonstrate the solubility of different substances in water.
• Record observations from solubility tests.

Social Domain

• Collaborate effectively in group activities during practical demonstrations.

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:

• Various salt samples (e.g., anhydrous copper(II) sulfate, sodium hydroxide pellets, hydrated sodium carbonate, sodium chloride, calcium chloride)
• Beakers
• Test tubes and test tube rack
• Spatulas
• Stirring rods
• Distilled water
• Chemicals (NaOH, KOH, HCl, H2SO4) for salt preparation demonstration
• Bunsen burner, tripod stand, gauze mat, evaporating dish (for salt preparation demonstration)
• Watch glass
• pH paper or universal indicator (for pH application discussion)

Rationale for the Lesson

This lesson is important for students to understand the diverse physical properties of salts, particularly their interaction with water and atmospheric moisture. This knowledge is fundamental to various chemical processes, industrial applications, and everyday observations, enhancing their practical understanding of chemical substances.

Prerequisite/Previous Knowledge

Students should have a basic understanding of acids, bases, and salts, including their general definitions and common examples.

Lesson Content/Board Summary

Acids, Bases And Salts: Deliquescent, Efflorescent, Hygroscopic and Solubility of Salts in Water

Properties of Salts

Salts are ionic compounds formed from the reaction of an acid and a base. They generally exhibit the following properties:

1. Most salts are crystalline solids at room temperature.
2. They typically have high melting and boiling points.
3. Many salts are soluble in water, forming aqueous solutions.
4. In molten state or as aqueous solutions, salts conduct electricity due to the presence of mobile ions.
5. Salts can be neutral, acidic, or basic depending on the strength of the acid and base from which they are formed.

Preparation of Salts

Salts can be prepared through various methods, including neutralization reactions:

1. Neutralization Reaction: This involves the reaction between an acid and a base to form a salt and water.

General Equation: Acid + Base (rightarrow) Salt + Water

1. Example 1: Preparation of Sodium Chloride (NaCl)

Sodium chloride can be prepared by the reaction of hydrochloric acid with sodium hydroxide:

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

1. Example 2: Preparation of Copper(II) Sulfate (CuSO4)

Copper(II) sulfate can be prepared by the reaction of sulfuric acid with copper(II) oxide (an insoluble base):

(text{H}_2text{SO}_4text{(aq)} + text{CuO(s)} rightarrow text{CuSO}_4text{(aq)} + text{H}_2text{O(l)})

Solubility of Salts in Water

Solubility refers to the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature to form a saturated solution.

1. Factors Affecting Solubility:

• Temperature: For most solid salts, solubility increases with an increase in temperature.
• Nature of Solute and Solvent: “Like dissolves like” – ionic salts are generally soluble in polar solvents like water.

1. General Solubility Rules for Salts:

• All nitrates ((text{NO}_3^-)) are soluble.
• All alkali metal (Group 1) salts and ammonium ((text{NH}_4^+)) salts are soluble.
• Most chlorides ((text{Cl}^-)), bromides ((text{Br}^-)), and iodides ((text{I}^-)) are soluble, except those of silver ((text{Ag}^+)), lead ((text{Pb}^{2+})), and mercury(I) ((text{Hg}_2^{2+})).
• Most sulfates ((text{SO}_4^{2-})) are soluble, except those of barium ((text{Ba}^{2+})), lead ((text{Pb}^{2+})), strontium ((text{Sr}^{2+})), and calcium ((text{Ca}^{2+})).
• Most carbonates ((text{CO}_3^{2-})), phosphates ((text{PO}_4^{3-})), and sulfides ((text{S}^{2-})) are insoluble, except those of alkali metals and ammonium.
• Most hydroxides ((text{OH}^-)) are insoluble, except those of alkali metals and barium.

Hygroscopic Substances

Hygroscopic substances are those that readily absorb moisture from the atmosphere without dissolving in it to form a solution. They simply become damp or moist.

1. Characteristics: They increase in mass when exposed to air due to water absorption.
2. Examples: Anhydrous copper(II) sulfate ((text{CuSO}_4)), silica gel, concentrated sulfuric acid ((text{H}_2text{SO}_4)).
3. Uses: Often used as drying agents (desiccants) to remove moisture from gases or other substances.

Deliquescent Substances

Deliquescent substances are a type of hygroscopic substance that absorb so much moisture from the atmosphere that they eventually dissolve in the absorbed water to form a solution.

1. Characteristics: They turn into a liquid solution when exposed to moist air.
2. Examples: Sodium hydroxide pellets ((text{NaOH})), potassium hydroxide pellets ((text{KOH})), calcium chloride ((text{CaCl}_2)), iron(III) chloride ((text{FeCl}_3)).
3. Distinction from Hygroscopic: All deliquescent substances are hygroscopic, but not all hygroscopic substances are deliquescent. Deliquescent substances absorb enough moisture to form a solution, while other hygroscopic substances only become damp.

Efflorescent Substances

Efflorescent substances are hydrated crystalline solids that lose their water of crystallization to the atmosphere when exposed to air, turning into an anhydrous or lower hydrate form and often becoming powdery.

1. Characteristics: They lose mass and may change appearance (e.g., from crystalline to powdery) upon exposure to dry air.
2. Examples: Washing soda ((text{Na}_2text{CO}_3 cdot 10text{H}_2text{O})), Glauber’s salt ((text{Na}_2text{SO}_4 cdot 10text{H}_2text{O})), hydrated copper(II) sulfate ((text{CuSO}_4 cdot 5text{H}_2text{O})).
3. Conditions: Efflorescence occurs when the vapour pressure of the hydrated salt is greater than the partial pressure of water vapour in the surrounding atmosphere.

Applications of pH Value

The knowledge of pH value is crucial in various fields:

1. Agriculture: Soil pH affects nutrient availability and crop growth. Farmers adjust soil pH for optimal yields.
2. Medicine: The pH of blood and other body fluids must be maintained within a narrow range for proper bodily functions.
3. Industry: pH control is essential in many industrial processes, such as brewing, paper manufacturing, and wastewater treatment.
4. Daily Life: pH is important in household products (e.g., soaps, detergents, shampoos) and food preservation.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Review

Teacher’s Activity: The teacher greets the students and asks them to recall what they know about salts, their formation, and general properties. The teacher then introduces the topic of the day, explaining that they will explore specific properties of salts related to water and atmospheric moisture.

Pupils’ Activity: Pupils respond to questions about salts and listen attentively to the introduction.

Learning Point: Basic salt concepts reviewed

Step 2: Properties and Preparation of Salts

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the general properties of salts and demonstrates the preparation of a simple salt like sodium chloride or copper(II) sulfate using neutralization, highlighting the reactants and products. The teacher guides students to observe the process.

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

Learning Point: Salt properties and preparation

Step 3: Solubility of Salts in Water

Time: 10 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher defines solubility and explains the factors affecting it, such as temperature and the nature of the solute/solvent. The teacher discusses general solubility rules for common salts.

Pupils’ Activity: Pupils listen, take notes, and participate in discussions about solubility.

Learning Point: Definition and factors of solubility

Step 4: Practical Demonstration of Solubility

Time: 10 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher guides students to test the solubility of different salt samples (e.g., NaCl, (text{CuSO}_4), (text{CaCO}_3)) in water at room temperature. Students observe which salts dissolve and which do not. The teacher encourages them to record their observations.

Pupils’ Activity: Pupils actively participate in the solubility tests, observe the changes, and record their findings.

Learning Point: Observing salt solubility

Step 5: Hygroscopic and Deliquescent Substances

Time: 8 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher introduces hygroscopic and deliquescent substances, defining each term. The teacher demonstrates with samples like anhydrous copper(II) sulfate (hygroscopic) and sodium hydroxide pellets (deliquescent), showing their interaction with atmospheric moisture over a short period. The teacher guides students to search for meanings of these terms (Activity 2).

Pupils’ Activity: Pupils listen, observe the demonstrations, define the terms, and note examples.

Learning Point: Hygroscopic and deliquescent definitions

Step 6: Efflorescent Substances and pH Applications

Time: 7 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher defines efflorescent substances and provides examples like washing soda. The teacher differentiates between hygroscopic, deliquescent, and efflorescent properties. Finally, the teacher briefly discusses various applications of pH value in daily life and industry.

Pupils’ Activity: Pupils listen, ask questions, and note the distinctions and pH applications.

Learning Point: Efflorescent and pH applications

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 hygroscopic, deliquescent, and efflorescent substances.
2. Explain what is meant by the solubility of salts in water.
3. State two general properties of salts.
4. Give two examples of deliquescent substances.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding 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 deliquescent, efflorescent, hygroscopic substances, and solubility 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: Consolidation

Teacher’s Activity: The teacher briefly recaps the main points of the lesson, emphasizing the distinct ways salts interact with water and moisture, and their importance in chemistry and everyday applications. The teacher encourages students to observe these phenomena around them.

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

Learning Point: Consolidating salt properties

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook:

1. Differentiate clearly between hygroscopic, deliquescent, and efflorescent substances, providing two examples for each.
2. List three factors that affect the solubility of a salt in water.
3. Explain why sodium hydroxide pellets are stored in airtight containers.
4. Suggest two real-life applications where understanding the solubility of salts is important.
5. Describe how you would prepare a sample of sodium sulfate ((text{Na}_2text{SO}_4)) from sulfuric acid and sodium hydroxide.

Lesson Keywords

• Hygroscopic – Substances that absorb moisture from the atmosphere without dissolving.
• Deliquescent – Substances that absorb enough moisture from the atmosphere to dissolve and form a solution.
• Efflorescent – Hydrated substances that lose their water of crystallization to the atmosphere.
• Solubility – The maximum amount of solute that can dissolve in a given solvent at a specific temperature.
• Neutralization – A reaction between an acid and a base to form salt and water.
• pH Value – A measure of the acidity or alkalinity of a solution.

Differentiation

For students who may struggle, provide simplified definitions and focus on identifying examples through visual aids. Encourage peer support during practical activities. For advanced learners, challenge them to research and present on more complex solubility rules or industrial applications of these salt properties, such as the use of desiccants in packaging.

Suggested Lesson Videos

For further understanding, students can search on YouTube for:

• “Hygroscopic Deliquescent Efflorescent substances chemistry”
• “Solubility of salts in water SS1 Chemistry”
• “Preparation of salts by neutralization”