Acid Base and Salt Class 10 || Science|| Chapter 2 Notes

 Acid Base and Salt Class 10 ||Science|| Chapter 2 Notes

---

1. What are Acids and Bases?

a) Acids

• Acids are substances that have a sour taste and turn blue litmus paper red.

• Chemically, acids produce H⁺ ions (hydrogen ions) when dissolved in water.

  Examples:

  • Hydrochloric acid (HCl) – found in our stomachs to help digest food.
  • Sulphuric acid (H₂SO₄) – used in car batteries.
  • Acetic acid (CH₃COOH) – found in vinegar.

b) Bases

• Bases have a bitter taste, are slippery to touch, and turn red litmus paper blue.

• They produce OH⁻ ions (hydroxide ions) when dissolved in water.

  Examples:

  • Sodium hydroxide (NaOH) – used in soaps.
  • Calcium hydroxide (Ca(OH)₂) – used in whitewashing walls.
  • Magnesium hydroxide (Mg(OH)₂) – used in antacids like milk of magnesia.

---

2. Indicators: Identifying Acids and Bases

Indicators are substances used to identify whether a solution is acidic or basic by changing color.

• Litmus: A natural dye extracted from lichens.

  • Turns red in acids and blue in bases.

• Phenolphthalein: A synthetic indicator.

  • Remains colorless in acids, turns pink in bases.

• Methyl Orange:

  • Turns red in acids, yellow in bases.

Natural Indicators:

• Turmeric turns red in a basic solution.
• China rose (Hibiscus) extract turns green in a basic solution and dark pink in an acidic solution.

---

3. Chemical Properties of Acids and Bases

a) Reactions of Acids

1. Reaction with Metals:

   • Acids react with metals to produce a salt and hydrogen gas.
   • Example:$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">HCl</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">Zn</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\to </span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">ZnCl</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">H</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}$$
     • Hydrochloric acid reacts with zinc to produce zinc chloride and hydrogen gas.

2. Reaction with Metal Carbonates and Bicarbonates:

   • Acids react with metal carbonates and bicarbonates to produce a salt, water, and carbon dioxide.
   • Example:$$\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">HCl</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">NaHCO</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">3</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\to </span></span>\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">NaCl</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">H</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">O</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">CO</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}$$
     • Hydrochloric acid reacts with sodium bicarbonate (baking soda) to produce sodium chloride, water, and carbon dioxide.

3. Reaction with Bases (Neutralization Reaction):

   • Acids react with bases to form salt and water.
   • Example:$$\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">HCl</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">NaOH</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\to </span></span>\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">NaCl</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">H</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">O</span></span>}$$
     • Hydrochloric acid reacts with sodium hydroxide to form sodium chloride (table salt) and water.

b) Reactions of Bases

1. Reaction with Acids:

   • Bases neutralize acids to form salt and water.

2. Reaction with Metals:

   • Bases react with certain metals like zinc to produce hydrogen gas.
   • Example:$$\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">NaOH</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">Zn</span></span>}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\to </span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">Na</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">ZnO</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">H</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}$$
     • Sodium hydroxide reacts with zinc to produce sodium zincate and hydrogen gas.

3. Reaction with Non-Metal Oxides:

   • Bases react with non-metal oxides to produce salt and water.
   • Example:$${\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">Ca(OH)</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">CO</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">\to </span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">CaCO</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">3</span></span>}}<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">+</span></span>{\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">H</span></span>}}_{\mathrm{<span\; style="background-color:\; white;"><span\; style="font-family:\; Kanit;\; font-size:\; medium;">2</span></span>}}\text{<span style="background-color: white;"><span style="font-family: Kanit; font-size: medium;">O</span></span>}$$
     • Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. This reaction is used in whitewashing.

---

4. The pH Scale: Measuring Acidity and Basicity

a) What is pH?

• The pH scale measures how acidic or basic a solution is, ranging from 0 to 14.
  • pH < 7: Acidic solution.
  • pH = 7: Neutral solution (like pure water).
  • pH > 7: Basic solution.

b) Importance of pH in Everyday Life

• Soil pH affects plant growth. Farmers add lime (CaO) to neutralize acidic soil.
• Human body: The pH of human blood is around 7.4, which is slightly basic.
• Digestive system: The stomach produces hydrochloric acid (pH around 1.5 to 3.5) to help in digestion. Antacids are taken to neutralize excess acid.

---

5. Salts: Formed from Acids and Bases

a) What Are Salts?

• Salts are ionic compounds formed when an acid reacts with a base.
  • Example: $\text{HCl}+\text{NaOH}\to \text{NaCl}+{\text{H}}_2\text{O}$
    • Sodium chloride (table salt) is formed from the neutralization of hydrochloric acid and sodium hydroxide.

b) Types of Salts

1. Normal Salts: Formed by complete neutralization of an acid and base.

   • Example: Sodium chloride (NaCl).

2. Acidic Salts: Formed when an acid is partially neutralized by a base.

   • Example: Sodium hydrogen sulfate (NaHSO₄).

3. Basic Salts: Formed when a base is partially neutralized by an acid.

   • Example: Basic magnesium chloride (Mg(OH)Cl).

---

6. Common Salts and Their Uses

• Sodium chloride (NaCl): Common salt used in food.
• Sodium bicarbonate (NaHCO₃): Known as baking soda, used in baking, cleaning, and as an antacid.
• Washing soda (Na₂CO₃·10H₂O): Used in detergents and cleaning agents.
• Plaster of Paris (CaSO₄·½H₂O): Used for making casts in hospitals and in construction.

---

7. Water of Crystallization

• Some salts contain water molecules in their crystalline structure, known as water of crystallization.
• Example:
  • Copper sulphate (CuSO₄·5H₂O) has five water molecules. When heated, it loses this water and turns from blue to white.
  • Gypsum (CaSO₄·2H₂O) is used to make Plaster of Paris when heated to 100°C, as it loses its water of crystallization.

---

8. Neutralization in Everyday Life

• Indigestion: Excess acid in the stomach can be neutralized with antacids like magnesium hydroxide (milk of magnesia).
• Soil Treatment: Acidic soil is neutralized with bases like quicklime (calcium oxide).
• Tooth Decay: Bacteria in the mouth produce acids that damage tooth enamel. Toothpaste, being basic, neutralizes this acid.

---

9. Conclusion

Acids, bases, and salts are an integral part of our daily lives, from the food we eat to the products we use. Understanding their chemical behavior helps us recognize their uses and handle them safely. By learning how acids react with bases to form salts, and the importance of pH in various biological and industrial processes, we gain insights into the chemical processes around us.