Buffer calculator
About this tool:
A buffer is an aqueous solution that consists of a mixture of a weak acid and its conjugate base. The purpose of a buffer is to keep the pH value (a measure of acidity or basicity) at a constant (or nearly constant) value.
The pH of human blood, for example, is regulated by carbonic acid (@@H_2CO_3@@), which acts as the weak acid, and bicarbonate (@@HCO_3^-@@), which acts as the conjugate base. Together, carbonic acid and bicarbonate maintain the pH of blood between 7.35 and 7.45.
Keep in mind that buffers are only effective within a certain pH range. This range depends on the dissociation constant (@@K_a@@) of the acid.
Acids (@@HA@@) dissociate in solution to give a conjugate base (@@A^-@@) and a hydrogen ion (@@H^+@@):
$$ HA \rightleftharpoons A^- + H^+$$ $$ K_a = \frac{[A^-][H^+]}{[HA]}$$ $$ pK_a = - log_{10} K_a$$In general, the useful pH range of a buffer is equal to pKa ± 1.0 units.
You can use this tool to calculate the mass of weak acid and conjugate base that are needed in order to prepare a buffer of a certain strength (concentration) to keep the pH at a desired value.
To learn more about buffers and how to prepare them, take a look here.
How to use this tool:
1. Select a buffer species from the list (citrate, phosphate, Tris, carbonate, etc). The calculator will show you the pKa, useful pH range and the properties of the acid and basic forms.
2. Input the desired pH value. It must be within the valid range!
3. Input the volume of buffer desired.
4. Input the buffer strength (concentration).
5. Click the "Get buffer recipe volume!"