Day 4: Acids, Bases, and pH | Middle Stage Science | Apex Institute of Maths and Sciences

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Day 4: Acids, Bases, and pH | Middle Stage Science | Apex Institute of Maths and Sciences

Day 4: Acids, Bases, and pH 🧪

Middle Stage Science | Apex Institute of Maths and Sciences

🎯 1. Concept: Chemical Nature

Chemical substances can be classified based on their nature into Acids and Bases. When an acid and a base react together, they cancel each other out to form salt and water. This is called Neutralization.

  • Acids: Sour in taste, turn blue litmus paper Red. (Example: Lemon juice, Vinegar).
  • Bases: Bitter in taste, soapy to touch, turn red litmus paper Blue. (Example: Baking soda, Soap).
  • Neutral Substances: Neither acidic nor basic. (Example: Pure water, Salt).

💡 2. Measuring Strength

The pH Scale measures how acidic or basic a substance is, ranging from 0 to 14:

  • pH < 7: Acidic (0 is the strongest acid).
  • pH = 7: Neutral.
  • pH > 7: Basic/Alkaline (14 is the strongest base).

🌍 3. Science in Our Daily Life

Antacids: When you have “acidity” in your stomach, you take an antacid. Since the stomach produces too much hydrochloric acid, the antacid (which is a base) performs a Neutralization reaction to make you feel better.

Soil Testing: Farmers test the pH of soil. If the soil is too acidic, they add “quicklime” (a base) to neutralize it so crops can grow.

📝 4. Home Indicator Task

Task: Red cabbage contains a natural indicator. Boil a few leaves in water to get purple juice. Add it to lemon juice and baking soda. Record the color changes! (Purple to Pink/Red = Acid; Purple to Green/Blue = Base).

✅ 5. Day 4 Research Assessment

Use the chemical logic provided above to answer the questions.

Easy
1. What is the taste of most acidic substances?
Solution: Acids are sour in taste, like lemons (Part 1).
Easy
2. Bases turn red litmus paper into which color?
Solution: Bases turn red litmus blue (Part 1).
Easy
3. What is the pH value of a neutral substance like pure water?
Solution: A pH of 7 is exactly neutral (Part 2).
Easy
4. Which of these is a common base found in kitchens?
Solution: Baking soda is a common base (Part 1).
Medium
5. A substance with a pH of 3 is considered:
Solution: Any value below 7 on the pH scale is acidic (Part 2).
Medium
6. The reaction between an acid and a base is called:
Solution: Neutralization occurs when an acid and base cancel each other (Part 1).
Medium
7. If you have stomach acidity, why do you take an antacid?
Solution: Antacids are bases that neutralize stomach acid (Part 3).
Medium
8. A substance with a pH of 12 is:
Solution: Values above 7 are basic; 12 is high on the basic side (Part 2).
Hard
9. Assertion: Lemon juice turns blue litmus red.
Reason: Lemon juice is acidic in nature.
Solution: Acids always turn blue litmus paper red (Part 1).
Hard
10. What are the two main products of a neutralization reaction?
Solution: Neutralization always results in the formation of salt and water (Part 1).
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