Grade 12 · Chemistry
Identifying acids and bases
Why it matters
Arrhenius and Brønsted-Lowry; conjugate pairs.
Advanced20m readingPrerequisite: None
What is pH?
Short answer
pH is a measure of how acidic or basic a solution is, defined as the negative base-10 logarithm of the hydrogen-ion concentration: pH = −log[H⁺]. The scale usually runs 0–14; pH below 7 is acidic, 7 is neutral, and above 7 is basic. Each whole-number change in pH represents a tenfold change in [H⁺].
🔒
This feature is available in the School Plan.
Upgrade to unlock the full lesson, examples, quiz and practice.
Upgrade PlanRelated topics
Frequently asked questions
- Why is each pH unit a factor of ten?
- Because pH is a base-10 logarithm: a pH change of 1 means [H⁺] changes by a factor of 10.
- What is the relationship between pH and pOH?
- At 25 °C, pH + pOH = 14.