Acids Bases and Salts — Maharashtra (SSC) Class 9 Science Solutions (Free)

Acids: Sour taste, turn litmus paper red, release H⁺ ions in water. Examples: HCl, H₂SO₄. Bases: Bitter taste, turn litmus paper blue, release OH⁻ ions in water. Examples: NaOH, NH₃. Neutralization: acid + base → salt + water.

pH is a measure of acidity/basicity of a solution. pH = -log[H⁺]. Scale: 0-14 (pH < 7 = acidic, pH = 7 = neutral, pH > 7 = alkaline). Step 1: [H⁺] = 10⁻³ mol/L Step 2: pH = -log(10⁻³) = -(-3) = 3

Salts are ionic compounds formed by neutralization of acids and bases. General reaction: Acid + Base → Salt + Water. Examples: NaCl (from HCl + NaOH), CuSO₄ (from H₂SO₄ + Cu(OH)₂), KNO₃ (from HNO₃ + KOH). Salts are soluble in water and dissociate into cations and anions.

Indicators are substances that change color in acidic/basic solutions. Natural indicators: (1) Litmus paper—red in acid, blue in base; (2) Turmeric—yellow in neutral/acid, brown in base; (3) Red cabbage juice—red in acid, yellow-green in base; (4) Methyl orange—red in acid, yellow in base.

HCl + NaOH → NaCl + H₂O. This is neutralization: strong acid + strong base → salt + water. Heat is released (exothermic). Ionic equation: H⁺ + OH⁻ → H₂O. The salt formed (NaCl) is neutral because both acid and base are strong.