# Buffer pH Calculator

By Łucja Zaborowska, PhD candidate and Anna Pawlik, PhD candidate
Last updated: Aug 11, 2021

Our buffer pH calculator provides you with an effortless way to compute the pH of any kind of buffer solution. Decide whether your buffer is based on an 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 how to calculate the pH of a buffer solution, and give you all the essential buffer solution calculation tips.

## 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](calc:470). 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.

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 the most important.

Check out our arterial and venous blood pH calculators! 💉

Łucja Zaborowska, PhD candidate and Anna Pawlik, PhD candidate
Check out our list of popular buffers and their pK's in the article to your right 👉
Buffer type
Acid
Ka
pKa
Acid concentration
M
Salt concentration
M
pH
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