Deriving Henderson-Hasselbalch Equation Step by Step. The Relationship between pH, pKa, Titration Curve and Buffer Action of a Weak Acid. The Significance. Derivation of the Henderson –Hasselbalch Equation for weak base. B + HOH. BH . +. + OH. – or. B. –. + HOH. BH + OH. –. Either one works, but you have to be. Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity using the acid dissociation constant (pKa.

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Deriving the Henderson-Hasselbach Equation » Science Matters

In my next post, I will discuss the similarities and differences between using an ICE table versus using the Henderson-Hasselbach equation. Then take the negative logarithm of both sides: By our laws of logarithms, when two values are multiplied, it is the same as distributing the log to both values and taking the sum. Retrieved from ” https: The first step in deriving the Henderson-Hasselbach equation is to set up your equilibrium expression.

Similar problem is present in calculation of pH of hrnderson buffers. The Ka is the dissociation constant similar to the equilibrium constant for the ionization reaction of an acid. Our next steps are mathematical in nature.

The dissociation of an acid can be described by an equilibrium expression: Also remember, the buffer is a mixture of equimolar concentration of henrerson acid and its conjugate base. Taking the negative log of both sides of the equation gives.

Julian—Gregorian uncertainty Use dmy dates from September In this simulation, we will use KA for the acid dissociation constant. Here you will see me using the exponent rule Now a logarithm rule: You must be logged in to post a comment.



For the standard base equation: Please help improve it or discuss these issues on the talk page. Then, using the properties of logarithms:. WikiProject Chemistry may be able to help recruit an expert. For example, in the case of acetate buffer, the pKa is 4.

Further calculations depend on the way you want to prepare the buffer. The Henderson-Hasselbach equation will also enable you to calculate the pH of a weak acid or weak base solution.

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Our final step is to simplify our expression so that we are using pH and. Henderson-Hasselbalch equation is used mostly to calculate pH of solution which is obtained by mixing known amount of acid and conjugate base or neutralizing part of acid with strong base. The equation is also useful for estimating the pH of a buffer solution and to ascertain the equilibrium pH in acid-base reactions which will be of use to calculate the isoelectric point pI of proteins.

The Henderson-Hasselbach equation derived from the equilibrium expression of hydrofluoric acid. This article needs additional citations for verification. The more diluted the solution is, the more solution pH is dominated not by the presence of acetic acid and its conjugate base, but by the water auto dissociation. Articles needing expert attention with no reason or talk parameter Articles needing expert attention from February All articles needing expert attention Chemistry articles needing expert attention Articles needing additional references from February All articles needing additional references Articles with multiple maintenance issues All articles that may contain original research Articles that may contain original research from February CS1: However, the same equation will work perfectly regardless of the pKa value if you are asked to calculate ratio of acid to conjugate base in the solution with known pH.


The Henderson—Hasselbalch equation can be applied to relate the pH of blood to constituents of the bicarbonate buffering system: In the case of solutions containing not-so-weak acids or not-so-weak bases equilibrium concentrations can be far from those predicted by the neutralization stoichiometry.

Your email address will not be published. However, these are related by the equation: Lecture notes on human physiolog. Using the properties of these terms at 25 degrees Celsius, one can synthesise an equation for pH of basic solutions in terms of p K a and pH: This can be rearranged: Now a logarithm rule: The hemderson step is to take the negative logarithm of both sides. By using this site, you agree to the Terms of Use and Privacy Policy.

Multiply both sides by [HF] and then divide both hasselblch by [F-] to get by itself. This is useful in arterial blood gasbut these usually state p CO 2hfnderson is, the partial pressure of carbon dioxiderather than H 2 CO 3. The dissociation constant Ka of the above reaction will be:

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