Buffer Capacity Calculator
Calculate the buffer capacity and resistance to pH changes using the Van Slyke equation
Calculate Buffer Capacity
pH before adding acid/base (0-14)
pH after adding acid/base (0-14)
Mass of acid or base added to buffer
Total volume of buffer solution
Buffer Capacity Results
Formula used: β = n / ΔpH (Van Slyke equation)
pH Change (ΔpH): 0.00
Buffer Efficiency:
Buffer Efficiency Analysis
Example Calculation
Phosphate Buffer Example
Buffer System: 0.1 M Phosphate Buffer (pH 7.4)
Initial pH: 7.40
Added: 5 mg HCl (strong acid)
Final pH: 7.25
Solution Volume: 100 mL
Calculation
ΔpH = 7.40 - 7.25 = 0.15
n = 5 mg HCl ÷ 36.5 mg/mmol = 0.137 mmol
n per liter = 0.137 mmol ÷ 0.1 L = 1.37 mmol/L
β = 1.37 ÷ 0.15 = 9.13 mmol/(L·pH)
Common Buffer Systems
Acetate Buffer
pKa: 4.76
pH Range: 3.8 - 5.8
Capacity: 0.05 - 0.15 M/(L·pH)
Phosphate Buffer
pKa: 7.21
pH Range: 6.2 - 8.2
Capacity: 0.08 - 0.20 M/(L·pH)
Tris Buffer
pKa: 8.06
pH Range: 7.0 - 9.0
Capacity: 0.05 - 0.12 M/(L·pH)
HEPES Buffer
pKa: 7.55
pH Range: 6.8 - 8.2
Capacity: 0.06 - 0.18 M/(L·pH)
Carbonate Buffer
pKa: 10.33
pH Range: 9.3 - 11.3
Capacity: 0.04 - 0.10 M/(L·pH)
Glycine Buffer
pKa: 9.78
pH Range: 8.8 - 10.8
Capacity: 0.03 - 0.08 M/(L·pH)
Buffer Tips
Maximum capacity occurs at pH = pKa
Higher concentration = higher capacity
Effective range: pKa ± 1 pH unit
Choose buffer with pKa near desired pH
Understanding Buffer Capacity
What is Buffer Capacity?
Buffer capacity (β) quantifies how well a buffer solution resists pH changes when acids or bases are added. It's defined as the number of moles of strong acid or base needed to change the pH of one liter of buffer by one pH unit.
Why is it Important?
- •Maintains stable pH in biological systems
- •Critical for enzyme activity and protein stability
- •Essential for analytical chemistry procedures
- •Important in pharmaceutical formulations
Van Slyke Equation
β = n / ΔpH
- β: Buffer capacity (mol/(L·pH))
- n: Moles of acid/base added per liter
- ΔpH: Change in pH (final - initial)
Note: Maximum buffer capacity occurs when pH equals the pKa of the buffer system.
Factors Affecting Capacity
- Concentration: Higher concentration = higher capacity
- pH vs pKa: Maximum at pH = pKa
- Buffer ratio: 1:1 acid:base ratio is optimal