📖 Lesson 2: Physical and Chemical Properties of Acids, Bases, and Salts

👩🏽‍🏫 Introduction

Hello again, curious learner! 👋🏽

In our previous lesson, we learned the basic definitions of acids, bases, and salts. Today, we will dive deeper to explore their fascinating physical and chemical properties. Knowing these properties will allow you to handle these substances safely and use them effectively in everyday life—from cooking your favorite dish to cleaning household items or even understanding important natural processes!

By the end of this lesson, you’ll confidently identify acids, bases, and salts based on their characteristics and chemical behaviors.

📘 Core Concepts

🔹 Physical Properties

Physical properties are features we can observe without changing the chemical nature of a substance.

🔹 Chemical Properties

Chemical properties describe how a substance interacts with other substances chemically.

Properties of Acids:

• Reaction with Metals: Acids react with metals (like zinc or magnesium) to produce hydrogen gas.

  Example:

  2HCl(aq)+Zn(s)→ZnCl2(aq)+H2(g) 

• Reaction with Carbonates: Acids react with carbonate compounds to release carbon dioxide gas.

  Example:

  2HCl(aq)+CaCO3(s)→ CaCl2(aq)+CO2(g)+H2O(l)

Properties of Bases:

• Reaction with Acids (Neutralization): Bases react with acids to form salt and water.

  Example:

  NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)

• Reaction with Ammonium Salts: Bases react with ammonium salts to release ammonia gas.

  Example:

  Ca(OH)2(aq)+2NH4Cl(s)→CaCl2(aq)+2H2O(l)+2NH3(g)

Properties of Salts:

• Reaction with Water (Solubility): Salts often dissolve in water, forming ions, though solubility varies.

• Reaction upon Heating: Some salts decompose on heating to form gases or other simpler substances.

  Example (heating calcium carbonate):

  CaCO3(s) →Δ CaO(s)+CO2(g) 

🧪 Real-Life Example

🔹 Acids in Everyday Cleaning: Household vinegar (acetic acid) can remove stains and mineral build-up (like limescale) due to its acidic properties. It reacts chemically with calcium carbonate deposits, dissolving them away.

$$\text{Acetic Acid}+\text{Calcium Carbonate (stains)}\to \text{Calcium Acetate}+\text{CO₂ gas}+\text{Water}$$

🧩 Sample Problem Walkthrough

🧠 Problem:
Predict the products when hydrochloric acid (HCl) reacts with magnesium (Mg).

✅ Step-by-Step Solution:

• Step 1: Write down reactants clearly:

  $$HCl+Mg\to ?$$

• Step 2: Remember, acids react with metals to produce hydrogen gas (H₂) and a salt.

• Step 3: Magnesium and hydrochloric acid will form magnesium chloride (MgCl₂) and hydrogen gas:

  Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)Mg(s)+2HCl(aq)→MgCl2​(aq)+H2​(g)

• Step 4: Confirm product formation (hydrogen gas bubbles observed).

✔️ Answer:
The products formed are magnesium chloride (MgCl₂) and hydrogen gas (H₂).

✍🏽 Practice Exercises

1. True or False:

(a) Bases feel slippery on the skin.
(b) Salts turn red litmus blue.
(c) Acids produce hydrogen gas when reacting with metals.

Answers:
(a) True
(b) False (Salts are neutral and do not affect litmus paper)
(c) True

2. Complete the following reaction:

H₂SO₄ (aq)+Zn (s)→?+?

Answer:

H2SO4(aq)+Zn(s)→ZnSO4(aq)+H2(g)

3. Short Answer:

Why do acids, bases, and salts conduct electricity in solution?

Sample Answer:
They produce ions (charged particles) when dissolved in water, allowing electricity to flow through the solution.

🌀 Recap

Today we learned:

• Physical properties of acids, bases, and salts (taste, feel, litmus paper test, conductivity).

• Chemical properties like acids reacting with metals or carbonates, bases reacting with acids or ammonium salts, and salts decomposing upon heating.

• Everyday examples like vinegar cleaning and antacid medications illustrate these properties.

💭 Reflection Prompt

Think about your kitchen or bathroom at home. Can you find one acid, one base, and one salt product? List these items in your science journal and explain how knowing their properties helps you use them safely and effectively. Share your thoughts with a classmate or family member!