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Buffer Preparation For Pharmacy Calculator

Work out buffer preparation for pharmacy instantly with clear inputs, formula shown and shareable results.

About Buffer Preparation For Pharmacy Calculator

Applies the Henderson-Hasselbalch equation to split a total buffer concentration into the acid and conjugate base needed for a target pH.

Formula

Henderson-Hasselbalch

pH = pKa + log([A-]/[HA]); so [A-]/[HA] = 10^(pH - pKa), and the two concentrations sum to the total buffer molarity

Worked example

With the default values below, Buffer Preparation For Pharmacy Calculator returns Conjugate base to acid ratio of 1.7378. Change any input above and every figure here is recalculated in your browser.

Inputs used

pKa of the buffer acidaccepts 1–13
4.76
Target pHaccepts 1–13
5
Total buffer concentrationaccepts 0.001–2 mol/L
0.1 mol/L

Results

Conjugate base to acid ratio
1.7378
Conjugate base concentration
0.06347 mol/L
Acid concentration
0.03653 mol/L
Buffer capacity
Within one pH unit of the pKa, so buffer capacity is good

Step by step

  1. 1Values used
  2. 2Henderson-Hasselbalch
  3. 3Conjugate base to acid ratio= 1.7378
  4. 4Conjugate base concentration= 0.06347 mol/L
  5. 5Acid concentration= 0.03653 mol/L
  6. 6Buffer capacity= Within one pH unit of the pKa, so buffer capacity is good

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Why stay within one pH unit of the pKa?

Outside that range one species dominates and the buffer resists pH change poorly.

Does ionic strength matter?

Yes. Activity coefficients shift the effective pKa, so a prepared buffer should always be checked with a pH meter.

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