pKa Full Form

What is Full Form of pKa?

pKa is a value that explains the acidity of a particular molecule or compound. It measures the strength of an acid.The pKa value indicates how tightly a bromine acid grasps a proton.

pKa is used for obtaining the acidity of a molecule or a compound because it evaluates acid dissociation through small decimal numbers.

In simple words, we can say pKa tells us how weak or strong an acid is. pKa is necessary for the comprehension of fundamental reactions in chemistry. The value of pKa is the negative base-10 logarithm of the acid dissociation constant of a molecule or a compound.

\begin{equation}

\begin{aligned}

&\text{pKa} = \text{-log10Ka}

\end{aligned}

\end{equation}

About pKa

pKa was discovered by chemists Edmond H. Fischer and Edwin G. Krebs in 1968. pKa is a symbol for the constant for acid dissociation on a logarithmic scale. It describes the fundamental reaction’s acidity on the basis of Bronsted theory.

Importance of pKa

The pKa value is of fundamental importance in early discovery and development for

1. Forecasting of ADMET (absorption, distribution, metabolism, excretion, and toxicity)

2. Assessment of potential changes in formulation or process development.

3. Prediction of chromatographic and electrophoretic separation behaviour.

4. Prediction of the strength and acidity of a molecule or a compound.

How pKa explains the acidity of a molecule or a compound

One of the Henderson-Hasselbalch Equation’s applications is the ability to find out the relative acidity of compounds through a comparison of their pKa values. Any compound that stabilises the conjugate base will increase the acidity, and vice-versa. Using acid-base mediocrity to predict acid-base reactions, we could say the lower value of pKa depicts the stronger acid and the higher value of pKa depicts the weaker acid.

Factors affecting pKa

The value of pKa for a molecule or a compound is affected by the temperature. If we change the temperature, the value of pKa would be changed accordingly.

According to Le Chatlier’s principle:

• If the dissociation of acid is exothermic

  • The higher temperature is unfavourable for dissociation. The high temperature would decrease the value of Ka, resulting in an increase in the value of pKa.

  • The lower temperature is favourable for dissociation. The low temperature would increase the value of Ka, resulting in a decrease in the value of pKa.

• If the dissociation of acid is endothermic

  • The higher temperature is favourable for dissociation. The high temperature would increase the value of Ka, resulting in a decrease in the value of pKa.

  • The lower temperature is unfavourable for dissociation. The low temperature would decrease the value of Ka, resulting in an increase in the value of pKa.

pKa values of various acids

Following are the pKa values of various acids at 25℃

Some important terms

1. Exothermic reactions: the chemical reactions that produce heat. In these reactions, the enthalpy change (ΔH) is negative.

2. Endothermic reactions: The chemical reactions in which reactants absorb heat to produce products. In these reactions, the enthalpy change (ΔH) is positive.

3. Dissociation of compounds: The process by which a molecule or compound, such as salts, splits (dissociates) into atoms and ions.