Chemistry · Class 7–10

The pH Scale — Acids & Bases

See how the pH scale measures how acidic or basic a substance is, from 0 to 14.

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🧠 Remember it

The pH Scale — Acids & Bases

0–6 is acid, 7 is neutral, 8–14 is base. Lower pH = stronger acid. "Below 7 is sour like lemon, above 7 is soapy like bleach, 7 is plain water."

🌏 In real life

An antacid tablet (a base) relieves acidity because your stomach's HCl has pushed the pH too low — the base neutralises the excess acid. Curd, lemon and tamarind taste sour because they are acidic (low pH).

📝 Quick notes

  • The pH scale runs from 0 to 14 and measures the concentration of H⁺ ions.
  • pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic (alkaline).
  • Lower pH means more acidic (more H⁺); higher pH means more basic (more OH⁻).
  • Acids turn blue litmus red; bases turn red litmus blue.

🎯 Test yourself

What does a pH of 7 indicate?

A neutral solution — neither acidic nor basic, e.g. pure water.

Learn it fully — free

See the animated, step-by-step The pH Scale — Acids & Bases lesson on Syllab

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