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The pOH Concept

Similar to the hydrogen-ion concentration, the concentration of the hydroxide ion can be expressed logarithmically by the pOH. The pOH of a solution is the negative logarithm of the hydroxide-ion concentration:

< extpOH = - extlog left< ceOH^- ight>>

The pH of a solution have the right to be related to the pOH. Consider a solution via a pH (= 4.0). The (left< ceH^+ ight>) of the solution would certainly be (1.0 imes 10^-4 : extM). Dividing (K_ extw) by this returns a (left< ceOH^- ight>) of (1.0 imes 10^-10 : extM). Finally the pOH of the solution equates to (- extlog left( 1.0 imes 10^-10 ight) = 10). This instance illustrates the following relationship.

< extpH + extpOH = 14>

The pOH range is equivalent to the pH range in that a pOH of 7 is indicative of a neutral solution. A basic solution has a pOH less than 7, while an acidic solution has a pOH of greater than 7. The pOH is convenient to use once finding the hydroxide ion concentration from a solution with a known pH.


Example (PageIndex1)

Find the hydroxide concentration of a solution via a pH of 4.42.

Solution

Step 1: List the well-known values and plan the trouble.

Known

pH (= 4.42) pH (+) pOH (= 14)

Unknown

(left< ceOH^- ight> = ? : extM)

First, the pOH is calculated, adhered to by the (left< ceOH^- ight>).

Tip 2: Solve.

<eginalign extpOH &= 14 - extpH = 14 - 4.42 = 9.58 \ left< ceOH^- ight> &= 10^- extpOH = 10^-9.58 = 2.6 imes 10^-10 : extM endalign>

Tip 3: Think about your result.

The pH is that of an acidic solution, and also the resulting hydroxide-ion concentration is less than (1 imes 10^-7 : extM). The answer has 2 considerable numbers because the offered pH has 2 decimal areas.

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The diagram listed below mirrors all of the interrelationships in between (left< ceH^+ ight>), (left< ceOH^- ight>), pH, and also pOH.

what is the [oh-] in a solution that has a ph of 12.80?