# Buffer Capacity Calculator

Created by Julia Żuławińska
Reviewed by Bogna Szyk and Jack Bowater
Last updated: Dec 30, 2022

The buffer capacity calculator is here to help you calculate and understand how much your buffer will resist a change in pH. Keep reading to find out why we need buffers, and how to calculate their capacity with the buffer capacity equation.

This tool requires at least some knowledge of what pH is and how to determine the pH of a solution. We recommend you explore these topics before delving into the calculator proper, as it will make it easier for you to understand what is buffer capacity.

## What is buffer capacity? - buffer capacity definition

Before we find out what is buffer capacity, we first need to establish what is a buffer. A buffer is a solution resistant to changes in pH. It consists of a weak acid, its salt, and a strong base, or a weak base, its salt, and a strong acid. You might not realize it, but buffers are used to control the pH of cosmetics, medicines, and food products. Even our blood's pH is kept between 7.35 and 7.45 by blood buffers! (Learn more in the blood ph calculator).

Buffer capacity quantifies the resistance of a buffer solution to changes in pH after the addition of OH- or H+. The capacity of a buffer and its initial pH impact the pH change after the addition of an acid or base.

More concentrated buffers have a higher capacity, as they have more molecules that can interact with additional acids or bases. That means that when a buffer has a higher concentration, the change in pH is slower.

## Buffer capacity equation

To find buffer capacity, you need to divide the number of moles of the acid/base you've added per liter of buffer solution by the change in pH:

β = n / ΔpH, where

• β is buffer capacity
• n is the number of moles of an acid or a base added per liter of buffer solution
• ΔpH is the change in pH: ΔpH = final pH - initial pH

## How to calculate buffer capacity?

1. Determine the initial pH with the Henderson–Hasselbalch equation:
$\quad\small \text{pH} = \text{pK}_\text{a}+log_{10}(\frac{[\text{A}^-]}{[\text{HA}]})$

, where:

• $\small [\text{A}^-]$ is the concentration of a base in the buffer
• $\small[\text{HA}]$ is the concentration of a acid in the buffer
• $\small\text{pK}_\text{a}$ is the dissociation constant of acid
1. Calculate the final pH using the same method.
2. Use the buffer capacity equation to calculate the buffer capacity. Or input the number into our calculator, and you will have the answer in no time!

Now you know how to find buffer capacity! Before you go, check out the solution dilution calculator!

Julia Żuławińska
Amount of acid/base
mol/
liters
Initial pH
Final pH
Buffer capacity
mol/
liters
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