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The magnitude pKa, Chemistry

When working with acids and bases, two familiar values ​​are PH and Pka, which is the force that molecules have to dissociate (it is the negative log of the dissociation constant of a weak acid).

The amount of a non-ionized substance is a function of the dissociation constant (pka) of the toxicant and the pH of the medium. They are of great importance from the toxicological point of view since the non-ionized forms are more lipid soluble and, therefore, are able to cross the biological membrane.

Key points

  • The notion of pH refers to the potential of hydrogen and is used as a measure of alkalinity or acidity. The term refers to the concentration of hydrogen ions.
  • A hydrogen is somewhat more acidic the lower its pKa.
  • The relationship between pH and pK is given by the Henderson-Hasselbach Equation, which is different for acids or bases.
  • The relationship between these family values ​​originated from the Henderson-Hasselbach Equation, which is different for acids or bases.

“In a reaction between an acid and a base, the acid acts as a proton donor and the base acts as a proton acceptor.”


pKa = -log 10K a

  • pKa is the negative base 10 logarithm of the acid dissociation constant (Ka).
  • The lower the pKa value, the stronger the acid.
  • These kinds of scales, calculations, and constants refer to the strength of bases and acids and how alkaline or acid a solution is.
  • The main reason pKa is used is because it describes acid dissociation using small decimal numbers. The same type of information can be obtained from Ka values, however these are usually very small numbers given in scientific notation that are difficult for most people to understand.

For example

The pKa of acetic acid is 4.8, while the pKa of lactic acid is 3.8. Using the pKa values, it can be seen that lactic acid is a stronger acid than acetic acid.

pKa and buffer capacity

In addition to using pKa to measure the strength of an acid, it can be used to select buffers. This is possible due to the relationship between pKa and pH:

pH = pKa + log10 ([A -] / [AH]) Where the brackets are used to indicate the concentrations of the acid and its conjugate base.

The equation can be rewritten as: Ka / [H +] = [A -] / [AH] This shows that pKa and pH are equal when half of the acid has dissociated. The buffering capacity of a species, or its ability to maintain the pH of a solution, is greatest when the pKa and pH values ​​are close together. Therefore, when selecting a buffer, the best choice is one that has a pKa value close to the target pH of the chemical solution.