Chapter 2: Acids, Bases, and Salts – CBSE Class 10 Science

Chapter 2: Acids, Bases, and Salts – Class 10 Science Revision Notes

Welcome to your ultimate revision guide on Chapter 2: Acids, Bases, and Salts for CBSE Class 10 Science. These concise, high-yield notes are tailored to help you maximize marks in board and school exams. Each section covers the most important points you must remember, presented in simple language with clear examples. Let’s dive in!

1. Understanding Acids

An acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. According to the Brønsted–Lowry definition, an acid is a proton donor. Common examples include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH). Acids have the following key properties:

They taste sour.
They turn blue litmus paper red.
They conduct electricity because they produce free-moving ions in solution.

2. Key Features of Bases

A base is a proton acceptor, releasing hydroxide ions (OH⁻) in an aqueous solution. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂). Bases exhibit these characteristics:

They taste bitter and feel slippery.
They turn red litmus paper blue.
They also conduct electricity due to ion formation.

3. Formation and Properties of Salts

Salts are ionic compounds formed by the neutralization reaction between an acid and a base. A general reaction:

Acid + Base → Salt + Water

For example:

HCl + NaOH → NaCl + H₂O

Salts also have distinctive properties:

They are often crystalline solids with high melting points.
They dissolve in water to produce electrolytic solutions.
Their aqueous solutions can be acidic, basic, or neutral depending on the parent acid and base.

4. The pH Scale: Measuring Acidity and Alkalinity

The pH scale ranges from 0 to 14 and measures the concentration of hydrogen ions:

pH < 7: Acidic solution
pH = 7: Neutral solution
pH > 7: Basic solution

Each pH unit represents a tenfold change in H⁺ concentration. For example, a solution with pH 3 is ten times more acidic than one with pH 4.

5. Indicators: Natural and Synthetic

Indicators are substances that change color in acidic or basic media. They are crucial for titration experiments. Key indicators:

Litmus: Red in acids, blue in bases.
Phenolphthalein: Colorless in acidic/neutral solutions, pink in basic solutions.
Methyl Orange: Red in acidic, yellow in basic solutions.

6. Neutralization Reactions and Their Applications

Neutralization is the process where an acid and a base react to form salt and water. These reactions have many real-life applications:

Antacid tablets neutralize excess stomach acid.
Soil treatment: Basic lime is added to acidic soil to adjust pH.
Manufacture of soap uses alkali to neutralize fats (saponification).

7. Important Reactions You Must Remember

Here are some exam-centric reactions:

Acid + Metal → Salt + Hydrogen Gas
Example: 2HCl + Zn → ZnCl₂ + H₂↑
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
Example: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂↑
Acid + Metal Hydroxide → Salt + Water
Example: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

8. Everyday Examples and Importance

Understanding acids, bases, and salts is essential because they are everywhere:

Citric acid in citrus fruits gives the sour taste.
Sodium bicarbonate (baking soda) is used in baking and cleaning.
Bleaching powder (a salt) disinfects water.

9. Important Definitions and Formulae

Remember these key terms and formulae for quick recall:

Conjugate Acid-Base Pair: Acid and base that differ by one H⁺ ion.
pH = -log[H⁺]
Strength vs. Concentration: Strength refers to degree of ionization; concentration refers to amount of solute per liter of solution.

10. Exam Preparation Tips

Follow these strategies to score high:

Write balanced chemical equations for all reactions in the chapter.
Use diagrams of pH scale and titration curves in answers.
Practice with NCERT exemplar and previous year questions.
Highlight key points in answers using bolded keywords.

11. Quick Revision Checklist

Before the exam, go through this checklist:

Definitions of acids, bases, and salts.
Properties of acids and bases (litmus test, taste, conductivity).
Important reactions with metals, carbonates, hydroxides.
pH scale and calculation of pH.
Common indicators and their color changes.

12. Summary

This article has provided concise, exam-oriented notes on Chapter 2: Acids, Bases, and Salts. By focusing on definitions, reactions, important terms, and tips, you can enhance your conceptual clarity and maximize your score. Good luck with your studies!

Disclaimer: These notes are for quick revision purposes. Always refer to your NCERT textbook and consult your teacher for detailed explanations. This guide is not a substitute for full textbook study.