How to calculate pka of an acid?

Hint: First of all we should know about an acid for solving this question. An acid is a substance which donates a hydrogen ion (generally known as proton) to another substance. Their pH value is less than seven. A chemical can donate a proton only if the hydrogen atom is attached to an electronegative atom such as oxygen, chlorine or nitrogen.

Complete step-by-step answer:
Acids are used as the catalysts in organic and industrial chemistry.

Uses of acids are as follows:
-Benzoic acid is generally used to preserve food.
-Carbonic acid is generally used to make carbonate drinks.
-Ethanoic acid is generally used to clean metals before electroplating, household cleaning, processing leather and maintenance of swimming pools.
-Acids such as sulfuric, hydrochloric acid and phosphoric acids, affect the dehydration and condensation process.
-Sulfuric acids are generally used in car batteries. They are also used in manufacturing of paints, dyes, and drugs and also in producing fertilizers.
-The pka values are just the negative logarithm of the ka values. Thus, pka = -log ka.

Strong acids are used as a catalyst in a chemical reaction. Strong acids are generally defined by their pka values. The acid must be stronger in aqueous solution than a hydronium ion, so its pka must be lower than that of a hydronium ion. Therefore, the stronger acids have a pka of <-174.


Note: It may be noted that the concentration of acetate ion $\left[ {{A}^{-}} \right]$in equation $(ii)$is taken to be almost equal to the concentration of the salt in equation $(i)$ because the acetate ions coming from fully dissociated salt suppress the ionization of the weak acid. If concentration of salt is equal to that of the acid, then in such case $pH=pKa$. While deriving the above expression always be careful while performing the logarithms calculations and logarithms formulas of addition and subtraction.