ACIDS, BASES AND SALTS in 1 Shot FULL CHAPTER IN ANIMATION NCERT SCIENCE Class 10th Chapter 2

Acids, Bases, and Salts: Properties, Reactions, and pH Scale

Acids, bases, and salts are three classes of chemical compounds that play vital roles in our daily lives and in industrial processes. From the citric acid in lemons and the hydrochloric acid in our stomachs to the sodium hydroxide in soaps and the sodium chloride (common salt) on our tables, these substances are everywhere. This chapter in the CBSE Class 10 Science syllabus builds on the earlier understanding of chemical reactions and introduces the concept of acids and bases through their characteristic properties, their reactions with each other (neutralisation), the pH scale, and the preparation and uses of common salts.

Acids are substances that taste sour, turn blue litmus paper red, and release hydrogen ions (H⁺) when dissolved in water. Common laboratory acids include hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃). Bases are substances that taste bitter, feel soapy to the touch, turn red litmus paper blue, and release hydroxide ions (OH⁻) in water. Common bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂). Water-soluble bases are specifically called alkalis. Indicators are substances that change colour in the presence of acids or bases — litmus (blue to red in acid, red to blue in base), phenolphthalein (colourless in acid, pink in base), methyl orange (red in acid, yellow in base), and natural indicators like turmeric (yellow in acid, reddish-brown in base) and China rose petals. The reaction between an acid and a base produces salt and water — this is called a neutralisation reaction: Acid + Base → Salt + Water. For example, HCl + NaOH → NaCl + H₂O.

The pH scale measures how acidic or basic a substance is on a scale from 0 to 14, where 7 is neutral (pure water). Values below 7 indicate acidic solutions (lower pH means stronger acid), and values above 7 indicate basic solutions (higher pH means stronger base). The pH is defined as pH = −log[H⁺], meaning each unit decrease in pH represents a tenfold increase in hydrogen ion concentration. Stomach acid has a pH of about 1.5, lemon juice about 2, milk about 6.5, blood about 7.4, soap about 10, and sodium hydroxide solution about 14. The body carefully maintains blood pH between 7.35 and 7.45 — even small deviations can be life-threatening. Salts are ionic compounds formed from the neutralisation of an acid by a base. Sodium chloride (NaCl) is the most common salt. Other important salts include washing soda (Na₂CO₃·10H₂O) used in glass and detergent manufacturing, baking soda (NaHCO₃) used in cooking and antacids, bleaching powder (CaOCl₂) used for water disinfection, plaster of Paris (CaSO₄·½H₂O) used in casts and moulds, and slaked lime (Ca(OH)₂) used in white-washing and soil treatment. The chapter also covers the chlor-alkali process, where electricity is passed through brine (NaCl solution) to produce NaOH, Cl₂, and H₂ — all three are important industrial chemicals.

• Acids release H⁺ in water (taste sour, turn blue litmus red); bases release OH⁻ (taste bitter, turn red litmus blue).
• Neutralisation: Acid + Base → Salt + Water; indicators like litmus and phenolphthalein identify acidic or basic nature.
• The pH scale ranges from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral.
• Important salts: NaCl (common salt), NaHCO₃ (baking soda), Na₂CO₃ (washing soda), CaSO₄·½H₂O (plaster of Paris).
• The chlor-alkali process electrolyses brine to produce NaOH, Cl₂, and H₂ — all major industrial chemicals.