Question

How do you calculate \[pOH\]of $NaOH$ ?

Answer 1

Hint: The aqueous solution of acids, base and neutral solution consists of ${{H}^{+}}$ and $O{{H}^{-}}$ ions. Sodium hydroxide is a strong base which when dissolved in water, it forms a sodium hydroxide solution. The water dissociates to give ${{H}^{+}}$ and $O{{H}^{-}}$ ions.

Complete step-by-step answer:$pOH$ is used to calculate the number of hydroxide ions in the solution. It basically tells us the alkalinity of the solution. It is calculated by the negative logarithm of hydroxide ion concentration.
Let us see the formula –
$pOH=-\log \left[ O{{H}^{-}} \right]$
Where, $\left[ O{{H}^{-}} \right]$ is the concentration of hydroxide ion
A basic solution has $pOH$ value less than $7$ .
You can calculate the $pOH$ if you know the sodium hydroxide concentration. You should know the molarity of $NaOH$
Lets us discuss with an help of an example-
Calculate the $pOH$ of ${{10}^{-7}}M$ $NaOH$ solution
As we know that sodium hydroxide is a strong base, it will completely dissociate to give hydroxide ions.
 We will add the contribution of water, because it is an aqueous solution of sodium hydroxide.
$\Rightarrow \left[ O{{H}^{-}} \right]={{10}^{-7}}+{{10}^{-7}}$
$\Rightarrow \left[ O{{H}^{-}} \right]=2\times {{10}^{-7}}$
To find the concentration hydroxide ions, we use $pOH$ formula,
$pOH=-\log \left[ O{{H}^{-}} \right]$
$\Rightarrow pOH=-\log \left[ 2\times {{10}^{-7}} \right]$
$\Rightarrow pOH=7-\log 2$
$\Rightarrow pOH=7-0.3$
$\Rightarrow pOH=6.7$
This is how you can calculate the $pOH$ of sodium hydroxide solution.

Note:In this question, we have calculated the value of $pOH$ using concentration of hydroxide ions.
${{K}_{b}}$ is defined as the dissociation constant of a base. If the value of dissociation constant of a base is high then it is a strong base whereas if the value of dissociation constant of a base is low then it is a weak base.
Ionization is a process in which a neutral molecule breaks down and splits into charged ions in aqueous solution. According to Arrhenius theory, bases dissociate to give hydroxide ions.