Calculate the exact amounts of monosodium and disodium phosphate needed to prepare phosphate buffer solutions at specific pH and molarity.
Monosodium Phosphate Required
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Disodium Phosphate Required
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Monosodium Phosphate Concentration
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Disodium Phosphate Concentration
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Base to Acid Ratio
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Phosphate buffers are most effective in the pH range of 5.8 to 8.0, with optimal buffering capacity around pH 7.2. This range corresponds to the second dissociation constant (pKa2) of phosphoric acid.
The Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])) determines the ratio of dibasic phosphate (HPO4²⁻) to monobasic phosphate (H2PO4⁻) needed to achieve the desired pH.
Anhydrous salts contain no water molecules, while monohydrate contains one water molecule and dihydrate contains two per salt molecule. The hydrated forms have higher molecular weights, affecting the mass calculations.
Phosphate buffers have high buffering capacity because phosphoric acid is triprotic with three dissociation constants, providing multiple buffering regions and high salt concentrations.
Yes, phosphate buffers are widely used in molecular biology and biochemistry. However, they can inhibit some enzymes and may precipitate in the presence of divalent cations or ethanol.
Dissolve the calculated amounts of both phosphate salts in approximately 80% of the final volume of distilled water, adjust pH if needed, then dilute to the final volume.
Temperature, ionic strength, and the presence of other ions can affect the actual pH. The calculations assume ideal conditions and may need slight adjustments in practice.
Phosphate buffers are generally stable when stored properly at room temperature. However, they should be protected from microbial growth and contamination, especially in biological applications.