Lesson Outline 
Soils  Part 4: Soil pH
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Defining pHThe definition of pH is: The negative logarithm of the hydrogen ion activity (concentration) in equivalents per liter [eq./l] or written as an equation: pH = log[H_{+}] = log 1/[H_{+}] (3) The mathematical expression, pH of 7, is much easier to say than “a hydrogen ion concentration of 0.0000001 gram equivalents per liter” as shown in Equation 4. pH = 7.0 = log(.0000001 eq.H_{+}/1) (4) pH = 5.0 = log(.00001 eq.H_{+}/1) (5) pH = 9.0 = log(.000000001 eq.H_{+}/1) (6)

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