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Calcimator

Buffer Solution Calculator

Calculate buffer pH using the Henderson-Hasselbalch equation. Enter pKa, acid concentration, and conjugate base concentration.

Inputs

M
M

Results

Buffer pH

4.76

[A⁻]/[HA] Ratio1
Buffer Capacity (β)0.11515
Effective Range (Low)3.76
Effective Range (High)5.76
Ka1.7378e-5
How to Use This Calculator
  1. Enter the pKa of the weak acid in your buffer system.
  2. Set acid concentration [HA] and conjugate base concentration [A⁻] in mol/L.
  3. Review Buffer pH (from Henderson-Hasselbalch), [A⁻]/[HA] Ratio, Buffer Capacity (β), and Effective pH Range.
  4. For maximum buffer capacity, choose a weak acid with pKa within 1 pH unit of your target pH.

How the result changes with pKa of Weak Acid

pKa of Weak AcidBuffer pH
22
77
1313
1818

What each input means

pKa of Weak Acid
Negative log of the acid dissociation constant (e.g., acetic acid pKa = 4.76)
Acid Concentration [HA]
Molar concentration of the weak acid (undissociated form)
Conjugate Base Concentration [A⁻]
Molar concentration of the conjugate base (e.g., sodium acetate)

How this is calculated

Formula

pH = pKa + log₁₀([A⁻]/[HA])

Worked example, using the default values

  1. Identify Input Parameters
    pKa of Weak Acid = 4.76, Acid Concentration [HA] = 0.1, Conjugate Base Concentration [A⁻] = 0.1 = 3 input(s) provided
  2. Calculate Buffer pH
    Buffer pH
    4.76 = 4.76
  3. Calculate [A⁻]/[HA] Ratio
    [A⁻]/[HA] Ratio = r
    1 = 1
  4. Calculate Buffer Capacity
    Buffer Capacity
    0.11515 = 0.11515

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