Chapter 2: Acids, Bases and Salts
Simple, exam-focused CBSE Class 10 Science notes — star topics, concepts, common mistakes, and previous year question patterns, all on one page.
Chapter 2: Acids, Bases and Salts
â Star Topics / Most Important
- pH scale and its importance
- Reactions of acids and bases with metals
- Common salts — washing soda, baking soda, bleaching powder, plaster of Paris
- Water of crystallisation
Detailed Chapter Notes
Acids taste sour and turn blue litmus red; bases taste bitter, feel soapy, and turn red litmus blue. Both produce ions in water — acids give H+ (or H3O+) and bases give OH- ions.
Acid + metal → salt + hydrogen gas: Zn + 2HCl → ZnCl2 + H2 (tested with a burning matchstick giving a "pop"). Acid + metal carbonate/bicarbonate → salt + water + CO2, and CO2 turns lime water milky.
Neutralisation: acid + base → salt + water — this is why antacids (a mild base) relieve acidity by neutralising excess stomach HCl.
The pH scale runs 0-14. Below 7 = acidic, above 7 = basic, 7 = neutral. The body works within a narrow pH range, and even small shifts cause problems — tooth decay starts once mouth pH drops below 5.5.
Key salts: Sodium hydroxide (chlor-alkali process), Bleaching powder CaOCl2 (chlorine + dry slaked lime), Baking soda NaHCO3 (cooking, antacids, fire extinguishers), Washing soda Na2CO3.10H2O (recrystallised baking soda), Plaster of Paris CaSO4.½H2O (heating gypsum at 373K, sets hard with water, used for fractured bones).
Water of crystallisation is the fixed number of water molecules in one formula unit of a salt (like the 10 in washing soda). Heating removes this water and often changes colour — blue copper sulphate turns white.
Students often think all bases are alkalis — wrong. Every alkali is a base, but only water-soluble bases are alkalis. Also, plaster of Paris formula is CaSO4.½H2O, not full water — writing the full water molecule is a very common half-mark deduction.
Search on YouTube: Acids Bases and Salts Class 10 NCERT full chapter for a visual walkthrough of this chapter.
- Why does distilled water not conduct electricity, whereas rainwater does? (2 marks)
- What is the chemical name of baking soda? Write its one use (2 marks)
- Why is plaster of Paris stored in a moisture-proof container? (2 marks, HOTS)
- Draw the pH scale and mark the pH of milk, lemon juice, and blood (3 marks)
- A milkman adds a small amount of baking soda to fresh milk — why? (2 marks)