Chapter 2 acids bases and salts notes

 

Class 10 Science Chapter 2: Acids, Bases, and Salts – Short Notes

1. Acids:

• Substances that release hydrogen ions $(H^{+})$ in water.
• Examples: Hydrochloric acid (HCl), Sulfuric acid (H${}_2$SO${}_4$).
• Properties:
  • Sour taste.
  • Turns blue litmus red.
  • Reacts with metals to release hydrogen gas.

2. Bases:

• Substances that release hydroxide ions $(O{H}^{-})$ in water.
• Examples: Sodium hydroxide (NaOH), Calcium hydroxide [Ca(OH)${}_2$].
• Properties:
  • Bitter taste.
  • Soapy touch.
  • Turns red litmus blue.
  • Reacts with acids to form salt and water (neutralization).

3. Indicators:

• Substances used to determine whether a solution is acidic or basic.
• Examples:
  • Litmus paper: Red in acid, blue in base.
  • Phenolphthalein: Colorless in acid, pink in base.
  • Methyl orange: Red in acid, yellow in base.

4. pH Scale:

• A scale to measure the acidity or basicity of a solution.
• Ranges from 0 to 14:
  • pH < 7: Acidic.
  • pH = 7: Neutral.
  • pH > 7: Basic.
• pH of common substances:
  • Stomach acid: 1.5
  • Pure water: 7
  • Soap solution: 9-10

5. Neutralization Reaction:

• Reaction between an acid and a base to form salt and water. $$\text{Acid}+\text{Base}\to \text{Salt}+\text{Water}$$
•  Example: $\text{HCl}+\text{NaOH}\to \text{NaCl}+{\text{H}}_{2}O$

6. Salts:

• Salts are ionic compounds formed after the neutralization of an acid and a base.
• Types of salts:
  • Neutral salts: Formed by strong acid + strong base (e.g., NaCl).
  • Acidic salts: Formed by strong acid + weak base (e.g., NH${}_4$Cl).
  • Basic salts: Formed by weak acid + strong base (e.g., Na${}_2$CO${}_3$).

7. Common Salts:

• Sodium chloride (NaCl): Common table salt, used in food.
• Baking soda (NaHCO${}_3$): Used in cooking and as an antacid.
• Washing soda (Na${}_2$CO${}_3$·10H${}_2$O): Used in cleaning.

8. Water of Crystallization:

• The fixed number of water molecules in the formula of a salt.
  • Example: Gypsum (CaSO${}_4$·2H${}_2$O) has 2 molecules of water.
  • When gypsum is heated, it loses water to form Plaster of Paris (CaSO${}_4$·½H${}_2$O).

9. Plaster of Paris:

• Chemical formula: CaSO${}_4$·½H${}_2$O.
• Used in construction, medical casts, and artistic sculptures.