The pH Scale — Acids & Bases — Interactive Diagram
See how the pH scale measures how acidic or basic a substance is, from 0 to 14.
TL;DR: See how the pH scale measures how acidic or basic a substance is, from 0 to 14.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
The pH Scale — Acids & Bases: See how the pH scale measures how acidic or basic a substance is, from 0 to 14.
Why it matters: pH tells us if something is an acid, base or neutral — vital for chemistry, biology and everyday life (soil, soaps, antacids).
The pH Scale — Acids & Bases — Step by Step
- The pH scale runs from 0 to 14. Lower numbers are more ACIDIC; higher numbers are more BASIC (alkaline).
- pH 7 is NEUTRAL — pure water. Below 7: lemon (2), vinegar (3). These turn blue litmus red.
- Above 7 are BASES: soap (9), baking soda (9), lime water. These turn red litmus blue. Strong acids/bases can be dangerous!
Quick Notes — the Exam Crux
- 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.
- Neutralisation: acid + base → salt + water (pH moves toward 7).
- Everyday values: gastric acid ≈ 1–3, pure water 7, blood ≈ 7.4, soap ≈ 9–10.
- Tooth decay begins when the mouth's pH falls below 5.5.
Remember It (Memory Trick)
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."
Real-Life Example
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).
Test Yourself
What does a pH of 7 indicate?
A neutral solution — neither acidic nor basic, e.g. pure water.
Why does an antacid relieve an acidic stomach?
It is a mild base that neutralises the excess hydrochloric acid, raising the pH back toward neutral.
Which is more acidic — a solution of pH 2 or pH 5?
pH 2; the lower the pH, the more acidic (more H⁺ ions).
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