🔥 Chapter 2: Acids, Bases and Salts
🎯 Class 10 Science Best Notes (With Hindi Explanation)

🧪 1. What are Acids and Bases?
Acids are substances that taste sour and turn blue litmus red.
Bases are substances that taste bitter and turn red litmus blue.
🔹 Example of Acid: Hydrochloric acid (HCl)
🔹 Example of Base: Sodium hydroxide (NaOH)
👉 Hindi Explanation:
Acids wo padarth hote hain jo khatte hote hain aur blue litmus ko red bana dete hain.
Bases wo padarth hote hain jo kadwe hote hain aur red litmus ko blue bana dete hain.

🧾 2. Indicators
Indicators are substances that change color in acids or bases.
🔹 Example: Litmus, Phenolphthalein, Methyl Orange
👉 Hindi Explanation:
Indicators wo padarth hote hain jo acid ya base mein apna rang badalte hain.

🧪 3. Reaction of Acids and Bases with Metals
🔹 Acids + Metals → Salt + Hydrogen Gas
Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑
👉 Hindi Explanation:
Acids jab metals se react karte hain to namak aur hydrogen gas nikalti hai.

🔹 Bases + Metals → Salt + Hydrogen Gas (Less Reactive)
Example: Zn + NaOH → Na₂ZnO₂ + H₂↑

⚗️ 4. Reaction of Acids with Metal Carbonates and Metal Hydrogen Carbonates
🔹 Acid + Metal Carbonate → Salt + Water + CO₂
Example:
CaCO₃ + HCl → CaCl₂ + H₂O + CO₂↑
👉 Hindi Explanation:
Acid jab metal carbonate se react karta hai to namak, paani aur carbon dioxide gas banti hai.

💥 5. Neutralisation Reaction
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
👉 Hindi Explanation:
Jab acid aur base react karte hain to namak aur paani banta hai. Ise neutralisation kahte hain.

💧 6. pH Scale
The pH scale measures the concentration of H⁺ ions in a solution.

• pH < 7 → Acidic
  
  

• pH = 7 → Neutral
  
  

• pH > 7 → Basic
  👉 Hindi Explanation:
  pH scale batata hai kisi solution mein H⁺ ions kitne hain.
  pH kam hone ka matlab acid zyada hai, aur pH zyada hone ka matlab base zyada hai.
  
  

🧂 7. Important Salts and Their Uses

🔹 (i) Sodium Chloride (NaCl)
Common salt used in food.

🔹 (ii) Baking Soda (NaHCO₃)
Used in baking cakes.
Preparation: NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
👉 Hindi Explanation:
Baking soda ek salt hai jo cake banane mein use hota hai.

🔹 (iii) Washing Soda (Na₂CO₃.10H₂O)
Used in cleaning clothes.
👉 Hindi Explanation:
Kapde dhone ke liye washing soda ka use hota hai.

🔹 (iv) Plaster of Paris (CaSO₄.½H₂O)
Used in making casts.
👉 Hindi Explanation:
POP ka use toot gaye hathon pairon ko bandhne ke liye hota hai.

📘 Important Questions for Practice — With Answers

✅ 1 Mark Questions

1. What is the chemical formula of baking soda?
   👉 NaHCO₃
   
   

2. What is the nature of bases?
   👉 Bases are bitter and turn red litmus blue.
   
   

3. Name an indicator used in the laboratory.
   👉 Litmus / Phenolphthalein / Methyl orange
   
   

4. Write one use of Plaster of Paris.
   👉 It is used in making casts in hospitals.
   
   

✅ 2 Mark Questions

1. What happens when zinc reacts with hydrochloric acid?
   👉 Hydrogen gas is released and zinc chloride (ZnCl₂) is formed.
   Equation: Zn + 2HCl → ZnCl₂ + H₂↑
   
   

2. State the difference between acids and bases (any two).
   | Property | Acids | Bases | |----------------|---------------------------|--------------------------| | Taste | Sour | Bitter | | Litmus Effect | Turns blue litmus red | Turns red litmus blue |
   
   

✅ 3 Mark Questions

1. What is a neutralisation reaction? Explain with an example.
   👉 When an acid reacts with a base to form salt and water, it is called neutralisation.
   Example: HCl + NaOH → NaCl + H₂O
   
   

2. Write the uses and chemical formula of:
   (i) Baking soda: NaHCO₃ → Used in baking.
   (ii) Washing soda: Na₂CO₃.10H₂O → Used in cleaning clothes.
   (iii) Plaster of Paris: CaSO₄.½H₂O → Used in medical plaster.
   
   

✅ 5 Mark Questions

1. Explain how pH is useful in everyday life.
   👉
   (i) pH helps in detecting acidic or basic nature of soil.
   (ii) pH of mouth below 5.5 causes tooth decay.
   (iii) pH is used in acid rain analysis.
   (iv) pH is important in digestion.
   (v) pH of blood must remain near 7.4 for survival.
   
   

2. Describe the preparation and use of any three salts.
   👉
   (i) Baking Soda (NaHCO₃): Used in baking.
   (ii) Washing Soda (Na₂CO₃.10H₂O): Used in detergents.
   (iii) Plaster of Paris (CaSO₄.½H₂O): Used in plastering.