Question

How do you find pOH from pH?

Answer 1

pH is used to indicate the concentration of hydrogen ions in a solution. Similarly, pOH is used to indicate the concentration of hydroxide ions in a solution. Both are related to each other.

Complete step by step answer:
pH is used to indicate the acidity of a solution and pOH is used to indicate basicity of a solution.
The formula for pH is,
$pH = - \log \left[ {{H^ + }} \right]$
where $\left[ {{H^ + }} \right]$ is the concentration of hydrogen ions in the solution.
Value of pH ranges from $0$ to $14$ . pH value of $7$ indicates neutral solution. Values less than $7$ indicates acidic solutions and values greater than $7$ indicates basic solution. Higher the concentration of hydrogen ions, higher will be strength of acids and lower will be the pH.
Similar to pH, pOH can also be expressed as,
$pOH = - \log \left[ {O{H^ - }} \right]$
where $\left[ {O{H^ - }} \right]$ is the concentration of hydroxide ions in the solution.
pH and pOH of a solution are related to each other. For any solution, sum of pH and pOH will be equal to a constant. Value of that constant is $14$ . Hence we can write,
$pH + pOH = 14$
Form the above equation, we can derive the equation for pOH. It is given by,
$pOH = 14 - pH$
Using the above equation, we can calculate pOH from pH.

Additional information-
We can also write,
$pH + pOH = p{K_w}$
The value of $p{K_w}$ is equal to $14$ .
For water, the value of pH and pOH is equal to $7$

Note:
pH and pOH scales are similar. In the pOH scale, $7$ indicates a neutral solution similar to that of pH scale. pOH value less than $7$ indicates basic solution and pOH value greater than $7$ indicates acidic solution.