Henderson-Hasselbalch equation

(noun)

In chemistry, the Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa, the negative log of the acid dissociation constant) in biological and chemical systems. The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions (it is widely used to calculate the isoelectric point of proteins).

Related Terms

Examples of Henderson-Hasselbalch equation in the following topics:

  • The Henderson-Hasselbalch Equation

    • The Henderson–Hasselbalch equation connects the measurable value of the pH of a solution with the theoretical value pKa.
    • The Henderson–Hasselbalch equation mathematically connects the measurable pH of a solution with the pKa (which is equal to -log Ka) of the acid.
    • Distributing the negative sign gives the final version of the Henderson-Hasselbalch equation:
    • An example of how to use the Henderson-Hasselbalch equation to solve for the pH of a buffer solution is as follows:
    • Calculate the pH of a buffer system using the Henderson-Hasselbalch equation.

  • Relative Amounts of Acid and Base

    • The exact ratio of the base to the acid for a desired pH can be determined from the Ka value and the Henderson-Hasselbalch equation.

  • Absolute Concentrations of the Acid and Conjugate Base

    • Solving for x using the quadratic equation, we get [H+] = 2.1 x 10-5 M.
    • We know from the Henderson-Hasselbalch equation that the ratio of the concentration of the buffer determines the pH rather than the concentration.
    • Using the same equations as above, we get [H+] = 2.80 x 10-5 M, which gives a pH of 4.54.
    • So check the equation and see what product has had a proton added—it's the conjugate acid.

  • Acidosis

    • Metabolic acidosis is compensated for in the lungs, as increased exhalation of carbon dioxide promptly shifts the buffering equation to reduce metabolic acid.
    • The Henderson-Hasselbalch equation is useful for calculating blood pH, because blood is a buffer solution.

  • Acid-Base Reactions

    • A simple relationship known as the Henderson-Hasselbalch equation provides this information.
    • Two examples of Lewis acid-base equilibria that play a role in chemical reactions are shown in equations 1 & 2 below.

  • α-Amino Acids

    • In order to determine the nature of the molecular and ionic species that are present in aqueous solutions at different pH's, we make use of the Henderson - Hasselbalch Equation, written below.

  • Preparing a Buffer Solution with a Specific pH

    • The balanced equation for this reaction is:
    • In a third method, you can determine the exact amount of acid and conjugate base needed to make a buffer of a certain pH, using the Henderson-Hasselbach equation: