Acids, Bases and Salts – Class 10 Chemistry Chapter 2

Acids, Bases and Salts

Acids, bases, and salts are important categories of chemical compounds that we encounter daily. Understanding their properties, reactions, and applications is fundamental to chemistry.

What are Acids?

Acids are substances that produce H⁺ (hydrogen) ions when dissolved in water. Common acids include:

• Hydrochloric acid (HCl) — found in stomach
• Sulphuric acid (H₂SO₄) — king of chemicals
• Acetic acid (CH₃COOH) — found in vinegar
• Citric acid — found in citrus fruits

What are Bases?

Bases are substances that produce OH⁻ (hydroxide) ions in water. Common bases:

• Sodium hydroxide (NaOH) — caustic soda
• Calcium hydroxide (Ca(OH)₂) — slaked lime
• Magnesium hydroxide (Mg(OH)₂) — milk of magnesia (antacid)

Indicators

Indicator	Colour in Acid	Colour in Base
Litmus	Red	Blue
Methyl Orange	Red	Yellow
Phenolphthalein	Colourless	Pink

The pH Scale

pH stands for "potential of Hydrogen" and measures the concentration of H⁺ ions in a solution on a scale of 0 to 14.

• pH < 7: Acidic (stomach acid ≈ 1.5)
• pH = 7: Neutral (pure water)
• pH > 7: Basic (soap ≈ 9-10)

pH is crucial in daily life: our blood pH must remain 7.35–7.45, soil pH affects agriculture, acid rain (pH < 5.6) damages monuments like the Taj Mahal.

Neutralisation Reaction

When an acid reacts with a base, they form a salt and water:

Acid + Base → Salt + Water

HCl + NaOH → NaCl + H₂O

Important Salts

• Common Salt (NaCl): Used in food, de-icing, and as a raw material for making NaOH, baking soda, and washing soda.
• Baking Soda (NaHCO₃): Used in fire extinguishers, cooking, and as an antacid.
• Washing Soda (Na₂CO₃·10H₂O): Used in glass, soap, paper industries, and water softening.
• Plaster of Paris (CaSO₄·½H₂O): Used for casts, moulds, and in hospitals for fractured bones.
• Bleaching Powder (CaOCl₂): Used for water purification and bleaching.

Reference: NCERT Science Textbook for Class 10 – Chapter 2; S. Chand Chemistry by Lakhmir Singh.