Buffer pH Calculator

Created by Łucja Zaborowska, MD, PhD candidate and Anna Pawlik, PhD candidate
Reviewed by Bogna Szyk, Jack Bowater and Adena Benn
Last updated: Oct 21, 2022

Our buffer pH calculator provides you with an effortless way to compute the pH of any kind of buffer solution. To decide whether your buffer is based on acid & its conjugate base or the other way around, enter the data, and let the calculator do the job for you.

In the article below, we will instruct you on ** how to calculate the ph of a buffer solution** and give you all the essential buffer solution calculation tips.

If you wish to learn more about pH, be sure to explore the concept further with our pH calculator.

How to use the buffer pH calculator?

Our buffer calculator requires 5 easy steps:

  1. The big choice: is your buffer based on an acid or a base?
  2. Do you know the K, pK, or neither?
  3. If you don't know the pK, but you need it, check out our list of popular buffer's pK.
  4. Enter the molar concentrations of your reagents.
  5. Your pH is at the bottom of the tool!

Try our titration calculator for more advanced calculations regarding acids & bases, their volumes, and molarity. ⚗️

Examples of pK for different buffers - find your own

To make things even easier for you, we prepared a list of popular buffers and their pKs. They are arranged from most acidic to most alkaline.

Buffer

pKa (25°C)

TFA

0.5

Sulfonate

1.8

Aspartic acid

2.1, 3.9, 9.8

Phosphate

2.1, 7.2, 12.3

Chloroacetate

2.9

Citrate

3.1, 4.8, 6.4

Gluconic acid

3.6

Formate

3.8

Lactate

3.9

Acetate

4.8

Carbonate

6.4

Ammonia

9.2

Example:

If you want to compute the pH of a given sodium phosphate buffer, you just need to enter the pKa into the calculator that best suits the pH you want to calculate. Remember: buffers work best if the solution's pH is close to the buffer's pK (± 1).

How to calculate the pH of a buffer solution?

🅰️ The buffer pH equation is based on the Henderson-Hasselbalch formula

pH = pKa + log([A⁻]/[HA])

where:

  • pH = -log₁₀(H);
  • Ka – Acid dissociation constant;
  • [HA] – Concentration of the acid;
  • [A⁻] – Concentration of conjugate base; and
  • pKa = -log₁₀(Ka).

This particular equation works on solutions made of an acid & its conjugate base.

Tips & Tricks

  1. Log shortcuts describes the logarithm with a base of 10.
  2. If exactly one half of the acid is dissociated, pKa = pH.
  3. Double check whether the value you have is Ka or pKa. p in mathematics describes the negative logarithm with a base of 10.

If you want to calculate the pH of a basic buffer, we recommend using the following modification:

pH = 14 - pKb - log([B+]/[BOH])

Why 14?

Take a look at the equation describing the dissociation of water at 25 °C: [H₃O][OH⁻] = 10⁻¹⁴ When calculating the pH of a base-derived solution, we're in fact counting the number of OH⁻ particles! In reality, we're computing the pOH of the solution. To convert our result to the desired pH scale, we need to use the following equation:

pOH + pH = 14

(Psst! It's valid only for aqueous solutions at 25°C.)

What is a buffer?

A buffer is a solution of a weak acid and its salt (a weak acid and its conjugate base), or a weak base and its salt (a weak base and its conjugate acid).

Buffers are solutions that can preserve their original pH when mixed with an acid or base. The ability of the buffer to maintain its pH is called its buffer capacity. To learn more about buffer capacity, visit our buffer capacity calculator.

Where can you find buffers?

Buffers are commonly used in chemistry, but they're closer to you than you think! Our blood is a mixture that contains a variety of buffers, of which carbonic acid is one the most important.

Check out our arterial blood pH and venous blood pH calculators! 💉

FAQ

What does buffer consist of?

When we talk about buffers, we usually mean the mixture of a weak acid and its salt (a weak acid and its conjugate base) or a weak base and its salt (a weak base and its conjugate acid).

The buffer can maintain its pH despite combining it with additional acid or base.

What is the best pH of a buffer?

If you want to obtain the buffer with the ability to maintain its pH, you need to create a buffer whose pH is close to the buffer's pK (± 1).

The pK stands for the negative logarithm of the acid dissociation constant:
pKa = -log₁₀(Ka)

How to calculate the pH of a carbonate buffer?

  1. Let's start with the acid dissociation constant (Ka):
    • pKa of a carbonate buffer equals 6.4.
  2. Let's assume that both the acid's and conjugated base's concentrations are equal to 6 M.
  3. Utilize the equation:
    pH = pKa + log([A⁻]/[HA])
    pH = 6.4 + log(6 M/6 M)
    pH = 6.4 + log(1)
    pH = 6.4 + 0
    pH = 6.4
  4. The pH of our buffer is equal to 6.4.

What buffers are there in human blood?

There are four primary buffers that help maintain the pH of human blood:

  • Bicarbonate buffer;
  • Hemoglobin buffer;
  • Phosphate buffer; and
  • Protein buffers.
Łucja Zaborowska, MD, PhD candidate and Anna Pawlik, PhD candidate
Check out our list of popular buffers and their pKs in the article to your right 👉
Buffer type
Acid
Ka
pKa
Acid concentration
M
Salt concentration
M
pH
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