Question

How do you calculate a Ka value from pKa?

Answer 1

Hint: As we know that pKa value is used to indicate the strength of an acid. It is found that pKa is the negative log of the Ka (acid dissociation constant) value or we can say acid dissociation constant. A lower value of pKa indicates a stronger acid.

Complete Solution :
- As we see from the definition of pKa that pKa is the negative log of the Ka (acid dissociation constant) value. And we can write this expression as:
$p{{K}_{a}} = -{{\log }_{10}}{{K}_{a}}$
- Thus,
${{K}_{a}} = {{10}^{-p{{K}_{a}}}}$
- We should remember the definitions for logarithmic functions. Like, when we write${{\log }_{a}}b=c$ , then we specify that ${{a}^{c}} = b$ .
- It is found that a small pKa value means the reaction favours the reactant than that of the products. And also lowest pKa value means highest value of Ka, which in turn leads to high acidity.
- Hence, we can calculate a Ka value from pKa in the above discussed manner.

Additional information-
- It is found that Ka (acid dissociation constant) is also called ionization constant or acidity constant, is basically a quantitative measure of the strength of an acid in solution.

Note: - It is found that strong acids or strong bases will have low pKa, and weak acids and weak bases will have higher pKa values. It is also found that bases are having pH values more than 7, and acids are having pH values less than 7.