High school11 min

Calculating a pH: strong acid, weak acid, base

Go from concentration to pH and back, pick the right formula for the strength of the acid or base, and check the assumption you made.

The essentials

1

Definition of pH

pH=−log⁡[HX3OX+][HX3OX+]=10−pH mol/L\text{pH} = -\log [\ce{H3O+}] \qquad [\ce{H3O+}] = 10^{-\text{pH}}\ \text{mol/L} with [HX3OX+][\ce{H3O+}] in mol/L. The scale is logarithmic: one pH unit lower means 1010 times more HX3OX+\ce{H3O+} ions.
2

The scale at 25 °C

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3

Strong acid, strong base

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4

Weak acid

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5

Weak base

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