Imp Questions For All Chapters – General Science Class 8
Short Questions
1. What is an acid?
- An acid is a substance that tastes sour and turns blue litmus red.
2. What is a base?
- A base is a substance that tastes bitter and turns red litmus blue.
3. What is a neutral substance?
- A neutral substance is neither acidic nor basic, like water and common salt.
4. Give two examples of acids.
- Hydrochloric acid (HCl) and Sulphuric acid (H₂SO₄).
5. Give two examples of bases.
- Sodium hydroxide (NaOH) and Calcium hydroxide (Ca(OH)₂).
6. What is an indicator?
- An indicator is a substance that changes color in acids and bases (e.g., litmus, methyl orange).
7. What is the color of blue litmus in acid?
- It turns red in acid.
8. What is the color of red litmus in a base?
- It turns blue in a base.
9. What is neutralization?
- The reaction between an acid and a base that forms salt and water.
10. What are the products of a neutralization reaction?
- Salt and water.
11. Which acid is found in lemon?
- Citric acid.
12. Which acid is found in vinegar?
- Acetic acid.
13. Which acid is found in tamarind?
- Tartaric acid.
14. What is the pH scale used for?
- The pH scale is used to measure how acidic or basic a substance is (range: 0-14).
15. Which acid is used in car batteries?
- Sulphuric acid (H₂SO₄).
Long Questions
1. How can we identify acids and bases using indicators?
- We can identify acids and bases using litmus paper, methyl orange, and phenolphthalein. Acids turn blue litmus red, while bases turn red litmus blue. Methyl orange turns red in acid and yellow in base, while phenolphthalein remains colorless in acid and turns pink in base.
2. Why is sulphuric acid important in industries?
- Sulphuric acid is used in fertilizers, paints, detergents, and car batteries. It is also used in petroleum refining, textile production, and metal cleaning, making it one of the most important industrial chemicals.
3. How can we check if an unknown liquid is an acid?
- To check if a liquid is an acid, we can use a litmus paper test or methyl orange test. If blue litmus turns red, or methyl orange turns red, the substance is acidic. We can also check with the pH scale, where acids have a pH below 7.
4. What are the main properties of acids?
- Acids are sour in taste, turn blue litmus red, and have a pH below 7. They react with metals to release hydrogen gas, with carbonates to produce carbon dioxide, and with bases to form salt and water in neutralization reactions.
5. What are the main properties of bases?
- Bases are bitter in taste, feel slippery, and turn red litmus blue. They have a pH above 7 and react with acids to form salt and water. Some bases, like sodium hydroxide and calcium hydroxide, are used in making soaps and cleaning agents.
6. How does neutralization help in daily life?
- Neutralization helps in relieving acidity, as antacids like milk of magnesia neutralize excess stomach acid. Farmers use lime to reduce soil acidity, and toothpaste neutralizes acids in the mouth to prevent tooth decay.
7. Why is hydrochloric acid important?
- Hydrochloric acid is used in cleaning metal surfaces, making chloride salts, and digesting food in the stomach. It is also used in laboratories and industries for chemical production and in household cleaning agents.
8. Why does metal corrode in saltwater?
- Metals corrode in saltwater because the salt and moisture react with the metal, forming rust or oxide layers. This weakens the metal, making it brittle and reducing its strength over time, which is why ships and bridges require anti-rust coatings.
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