Henderson Hasselbalch Equation Buffer

A buffer solution contains a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

Henderson hasselbalch equation buffer. The ph of a buffer solution can be estimated with the help of this equation when the concentration of the acid and its conjugate base or the base and the corresponding conjugate acid are known. 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. 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. Example problem applying the henderson hasselbalch equation.

The henderson hasselbalch equation can be also used in the case of polyprotic acids as long as the consecutive pk a values differ by at least 2 better 3. With bases if the value of an equilibrium constant is known in the form of a base association constant k b the dissociation constant of the conjugate acid may be calculated from pk a pk. Ph pk a log 0 25 0 35. Lawrence joseph henderson and karl albert hasselbalch.

He was responsible for developing the components of the equation after studying equilibrium reactions that took place within blood as a result of respiration specializing in fatigue. To the henderson hasselbalch equation return to the acid base menu problem 31. We must use the henderson hasselbalch equation to solve this problem. Thus it can be safely used in the case of phosphoric buffers pk a1 2 148 pk a2 7 199 pk a3 12 35 but not in the case of citric acid pk a1 3 128 pk a2 4 761 pk a3 6 396.

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. What is the henderson hasselbalch equation. This calculator is valid for a buffer of a weak acid and it s conjugate base of the same system for example if a system contains both ch 3 cooh and ch 3 coona then the ph of this buffer can be calculated. Note that here ch 3 cooh ca and ch 3 coona cb this equation is also known as henderson hasselbalch equation.

The henderson hasselbalch equation provides a relationship between the ph of acids in aqueous solutions and their pk a acid dissociation constant. The henderson hasselbalch equation can be used to calculate the ph of a solution containing the acid and one of its salts that is of a buffer solution. How much sodium formate hcoona 68 0069 g mol do you need to add to 400. Lawrence joseph henderson 1878 1942 was a talented biochemist among many other titles who spent most of his career at harvard.

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.