Henderson Hasselbalch Equation For Weak Base

By its nature it does not take into account the self dissociation of water which becomes increasingly important in dilute solutions.

Henderson hasselbalch equation for weak base. Calculate the ph of a buffer solution made from 0 20 m hc 2 h 3 o 2 and 0 50 m c 2 h 3 o 2 that has an acid dissociation constant for hc 2 h 3 o 2 of 1 8 x 10 5. Henderson hasselbalch equation is a simple expression which relates the ph pka and the buffer action of a weak acid and its conjugate base. If we use the henderson hasselbalch equation we do not need to worry about using the molar amounts of both the acid and the base. A buffer solution contains a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

The equilibrium between the weak acid and its conjugate base allows the solution to resist changes to ph when small amounts of strong acid or base are added. The henderson hasselbalch equation is an approximation. The reason the henderson hasselbalch equation is an approximation is because it takes water chemistry out of the equation. 1 this is a buffer solution with a weak base the ammonia and the salt of the weak base the ammonium chloride in solution at the same time.

The basic equation is as follows. The henderson hasselbalch equation also describes the characteristic shape of the titration curve of any weak acid such as acetic acid phosphoric acid or any amino acid. Assumptions for the henderson hasselbalch equation. Since a buffer is intended to give only a small change in ph with added h or oh the best buffer for a given ph is the one that gives the smallest change as may be seen from the henderson hasselbalch equation when the ph of the solution equals the pk of the buffer conjugate base acid and the buffer can therefore respond equally to both added acid and added base.

For example the solution may contain. The buffer ph can be estimated using the henderson hasselbalch equation which is ph pka log a ha. This works when water is the solvent and is present in a very large proportion to the h and acid conjugate base. The henderson hasselbalch equation equation ref hh is an approximation with a certain region of validity.

In chemistry and biochemistry the henderson hasselbalch equation can be used to estimate the ph of a buffer solution the numerical value of the acid dissociation constant k a of the acid is known or assumed the ph is calculated for given values of the concentrations of the acid ha and of a salt ma of its conjugate base a. Ph approx pk a log 10 dfrac a ha we have straightforward calculations for strong acids and bases but the computations behind buffers are rather complex and time consuming. At the half equivalence point the conjugate base concentration is equal to that of the weak acid. The henderson hasselbalch approximation allows us one method to approximate the ph of a buffer solution.

Ph pk a log 0 25 0 35. This means that the equation can be simplified.