Buffer Solution Calculator

Calculate pH, buffer capacity, and prepare buffer solutions using Henderson-Hasselbalch equation

Henderson-Hasselbalch Equation

pH = pKa + log([A⁻]/[HA])

Example Problems:
⭐ Basic Buffer pH
Acetic acid buffer: pKa=4.76, [HA]=[A⁻]=0.1M Phosphate buffer: pKa=7.21, equal concentrations NH₃/NH₄⁺ buffer: pKa=9.25, [base]=[acid]=0.1M
⭐⭐ Unequal Concentrations
Acetate: [HA]=0.2M, [A⁻]=0.1M Phosphate: [HA]=0.15M, [A⁻]=0.05M Formate: pKa=3.75, ratio 1:5
⭐⭐⭐ Reverse Calculations
Find ratio: pH=5.0, pKa=4.76 Blood pH: pH=7.4, phosphate pKa=7.21 Find pKa: pH=4.5, given concentrations
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Result

Enter values and click Calculate to see the result

Buffer Capacity Calculator

β = 2.303 × [Buffer] × ([H⁺][OH⁻]) / ([H⁺] + Ka)²

About Buffer Capacity
  • Maximum capacity when pH = pKa
  • Effective range: pKa ± 1
  • Higher concentration = higher capacity
  • Capacity measures resistance to pH change
Example Problems:
Maximum capacity: pH=pKa=4.76, [buffer]=0.1M Phosphate buffer: pH=7.4, pKa=7.21 High concentration: 0.2M acetate buffer Outside range: pH=3.0, pKa=4.76
Result

Enter values and click Calculate to see buffer capacity

Buffer Preparation Calculator
Example Problems:
1L of 0.1M acetate buffer, pH 4.76 500mL phosphate buffer, pH 7.4 250mL Tris buffer, pH 8.0 1L citrate buffer, pH 5.0
Preparation Instructions

Enter values and click Calculate to see preparation instructions

Common Buffer Systems
Buffer Name Chemical System pKa Effective pH Range Common Uses
Acetate CH₃COOH/CH₃COO⁻ 4.76 3.76 - 5.76 DNA/RNA work, electrophoresis
Citrate Citric acid/Citrate 3.13, 4.76, 6.40 2.1 - 7.4 Antigen retrieval, enzyme assays
Phosphate (PBS) H₂PO₄⁻/HPO₄²⁻ 7.21 6.2 - 8.2 Cell culture, biological work
HEPES HEPES acid/base 7.48 6.8 - 8.2 Cell culture, tissue culture
Tris Tris-H⁺/Tris 8.06 7.0 - 9.0 Biochemistry, molecular biology
Bicarbonate H₂CO₃/HCO₃⁻ 6.35 5.4 - 7.4 Blood, physiological systems
Carbonate HCO₃⁻/CO₃²⁻ 10.33 9.3 - 11.3 Alkaline solutions
Ammonia NH₄⁺/NH₃ 9.25 8.25 - 10.25 Basic pH applications
Borate Boric acid/Borate 9.24 8.2 - 10.2 Electrophoresis, biochemistry
Glycine Glycine-H⁺/Glycine 9.78 8.8 - 10.8 Western blotting, electrophoresis
MES MES acid/base 6.15 5.5 - 6.7 Biological buffers
MOPS MOPS acid/base 7.20 6.5 - 7.9 RNA work, enzyme reactions
Buffer Selection Tips
  • Choose pKa close to desired pH: Best buffering capacity when pH ≈ pKa
  • Consider temperature: pKa values change with temperature (especially Tris)
  • Check compatibility: Some buffers interact with metal ions or proteins
  • Physiological work: Use PBS or HEPES for cell culture
  • Molecular biology: Tris is widely used for DNA/RNA work

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