Key idea
pH, acids and bases
pH = −log₁₀[H₃O⁺] · [H₃O⁺] = 10⁻ᵖᴴ
pH is a logarithmic way of expressing hydrogen-ion activity; introductory calculations often approximate activity using concentration in sufficiently dilute solutions.
pH, acids and bases
The key idea
pH is a logarithmic way of expressing hydrogen-ion activity; introductory calculations often approximate activity using concentration in sufficiently dilute solutions.
Why it matters
Because the scale is logarithmic, a change of one pH unit corresponds to a tenfold change in the relevant hydrogen-ion activity ratio.
A picture to remember
Key idea
pH, acids and bases
Guided example
pH, acids and bases
pH is a logarithmic way of expressing hydrogen-ion activity; introductory calculations often approximate activity using concentration in sufficiently dilute solutions.
Put it into practice
pH, acids and bases
Choose a concrete case linked to pH, acids and bases. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.
Check your answer
A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.