Chapter 7 Acid Base Chemistry is one of the most important chapters in Class 9 Chemistry. It helps students understand the fundamental concepts of acids and bases, their reactions, and their role in daily life and the environment.
In this chapter, you will learn:
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What acids and bases are and how they behave in water.
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Different theories of acids and bases, including the Arrhenius and Bronsted-Lowry concepts.
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The key properties of acids and bases that make them useful in labs, industries, and everyday life.
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The causes and effects of acid rain, which is an important environmental issue.
These notes are carefully prepared to be easy to understand, student-friendly, and exam-focused. They will help you grasp the key ideas quickly, revise effectively, and perform confidently in your exams.
Whether you are new to the topic or preparing for exams, these notes make learning Acid Base Chemistry simple and clear.
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❓ Frequently Asked Questions (FAQs)
Q1. What is an acid?
An acid is a substance that releases H⁺ ions (protons) in water. It usually tastes sour and turns blue litmus paper red.
Example: HCl, H₂SO₄
Q2. What is a base?
A base is a substance that releases OH⁻ ions in water. It usually tastes bitter, feels slippery, and turns red litmus paper blue.
Example: NaOH, Ca(OH)₂
Q3. Give an example of a Bronsted-Lowry acid-base reaction.
NH₃ + H₂O → NH₄⁺ + OH⁻
Here, NH₃ is a base (accepts H⁺) and H₂O is an acid (donates H⁺).
Q4. What is acid rain?
Acid rain is rainwater containing excess acids like H₂SO₄ or HNO₃. It is caused by pollution from factories and burning fossil fuels and can harm buildings, plants, and water bodies.
Q5. Name one property of acids and bases
- Acids: Sour taste, turn blue litmus red, conduct electricity.
- Bases: Bitter taste, slippery feel, turn red litmus blue, conduct electricity.
Class 9 Chemistry – Chapter 7: Acid Base Chemistry MCQs
1. Which of the following is an acid?
(a) NaOH
(b) HCl ✅
(c) NH₄OH
(d) Ca(OH)₂
2. Which of the following is a base?
(a) H₂SO₄
(b) CH₃COOH
(c) NaOH ✅
(d) HCl
3. According to Bronsted-Lowry, an acid is:
(a) Proton acceptor
(b) Proton donor ✅
(c) Electron donor
(d) Electron acceptor
4. When metals react with acids, they:
(a) Dissolve
(b) Form salts
(c) Release hydrogen gas
(d) All of the above ✅
5. Acid rain is caused by:
(a) Excess acids in rainwater ✅
(b) Water pollution
(c) Earthquakes
(d) Sunlight
6. Which property is common to all acids?
(a) Bitter taste
(b) Turn red litmus blue
(c) Sour taste ✅
(d) Slippery feel
7. Which property is common to all bases?
(a) Sour taste
(b) Turn blue litmus red
(c) Slippery feel ✅
(d) Evolve hydrogen gas
8. A weak acid:
(a) Completely dissociates in water
(b) Partially dissociates in water ✅
(c) Does not react with metals
(d) Turns red litmus red
9. A strong base:
(a) Partially dissociates in water
(b) Completely dissociates in water ✅
(c) Tastes sour
(d) Turns blue litmus red
10. Example of Bronsted-Lowry acid-base reaction:
(a) NaOH + HCl → NaCl + H₂O
(b) NH₃ + H₂O → NH₄⁺ + OH⁻ ✅
(c) HCl + Zn → ZnCl₂ + H₂
(d) CH₃COOH → CH₃COO⁻ + H⁺