PEAZIT Aha card
Go straight to resources ↓pH: one step means a factor of ten
For a simple dilute-solution model, pH = −log₁₀[H₃O⁺]. A fall of 1 means ten times the H₃O⁺ concentration. At 25 °C a neutral aqueous solution is approximately pH 7.
| Observation | What it means |
|---|---|
| pH 3 | [H₃O⁺] ≈ 10⁻³ mol/L |
| pH 4 | [H₃O⁺] ≈ 10⁻⁴ mol/L |
One worked example
- 4 − 3 = 1There is one pH step.
- 10¹ = 10The difference is a factor, not addition.
- pH 3 versus pH 4The first has about 10× more H₃O⁺.
Watch out: Precisely, pH uses activity. Neutral pH depends on temperature; values can lie outside 0–14.
Goal, prerequisites and card origin
What you will learn: Compare acidity on a logarithmic scale.
What you need first: Powers of ten.
An original PEAZIT working card. Independent expert review and effectiveness testing have not yet taken place. · v1
Reference for the underlying principle ↗Show connections
For a simple dilute-solution model, pH = −log₁₀[H₃O⁺]. A fall of 1 means ten times the H₃O⁺ concentration. At 25 °C a neutral aqueous solution is approximately pH 7.