Question

How do you convert $pKa$ to $Ka$?

Answer 1

Hint: $pKa$ value gives us the strength of the acid i.e. it tells whether the given acid is a strong acid or a weak acid. $pKa$ value is the negative logarithm of the $Ka$ value i.e. $pKa = -\log 10\text{ Ka}$. By using this formula, we can easily convert $pKa$ to $Ka$. Now solve the given statement accordingly.


Complete Solution :
First of all, let’s discuss what is pH. pH gives us the measure of acid/base strength of any solution. pH scale ranges from 0-14, 7 is neutral, below 7 it represents acidic nature i.e. the compound is acidic and above 7 it represents basic nature i.e. the compound is basic.
- Now, coming next to the $pKa$ value. The $pKa$ tells us about the strength of the acid. The $pKa$ is the negative logarithm of the dissociation constant i.e. $Ka$ smaller value of $pKa$ indicates that it is a strong acid and it has a large $Ka$ value. On the other hand, a larger value of $pKa$ indicates that it is a weak acid and it has large $Ka$ value.
Considering the given statement as, We can convert $pKa$ to $Ka$ as:
As we know that,
$pKa = -\log 10\text{ Ka}$
Then;
$\begin{align}
 & -pKa = \log 10\text{ Ka} \\
 & {{10}^{(-pKa)}} = Ka \\
 & Ka = {{10}^{(-pKa)}} \\
\end{align}$

Note: In case of numericals , we can’t directly find the concentration of the $\text{ }\!\![\!\!\text{ H}_{aq}^{+}]$, first we have to find the $Ka$ value of $\text{ }\!\![\!\!\text{ H}_{aq}^{+}]$ from the given $pKa$ value and only after that we can find the concentration of the $\text{ }\!\![\!\!\text{ H}_{aq}^{+}]$ by applying the formula as ${{p}_{oH}} + {{p}_{H}} = 14$ . And, after finding the concentration of the hydrogen ion, we can easily find the pH of the solution by using the formula as:$pH = -\log [{{H}^{+}}]$.