Video narration
Why does lemon juice sting, while soap feels slippery-and why do both change indicator colours? Sourness and slipperiness are clues, not definitions; never taste or touch unknown chemicals. In water, acids produce hydrogen ions and bases produce hydroxide ions. That is the real distinction. Indicators show it: litmus is red in acid, blue in base; methyl orange, red to yellow; phenolphthalein, colourless to pink. Universal indicator places lemon juice below 7, water at 7, and soap above 7 on the pH scale, 0 to 14. Strong acids and bases ionise more completely than weak ones; strength is not concentration. Three reactions: Zn + 2HCl → ZnCl2 + H2; HCl + NaOH → NaCl + H2O; Na2CO3 + 2HCl → 2NaCl + H2O + CO2, causing fizzing. Neutralisation lets antacids counter stomach acid, improves acidic soil, and explains insect-sting treatments. Different ions in water drive reactions; indicators reveal which is present.