Buffer Range Problems

Effective Buffer Range

Effective buffer range: is the range of pH values where a buffer has the capacity to act as a buffer

Just focus on understanding 💡 the diagram, we will cover this in more detail when we talk about titrations :)

1. Only weak acid is present. We cannot form a buffer with only weak acid present
2. More and more strong base is added. We will eventually have added enough strong base to form a buffer:

$CH_3COOH\ \ +\ OH^-\ \rightarrow\ CH_3COO^-\ +\ H_2O\$

1. If we keep adding strong base (and raising the pH), eventually we will run out of weak acid. There will no longer be a buffer and the pH shoots up!

To calculate the effective buffer range (in pH), use this equation:

$\boxed{pKa\ \pm 1}$

Example:

What is the effective buffer range for a buffer that has a pKa of 2?

What about if you are given a pKb and asked for the buffer range?

You can use the same equation (pKa +/- 1), just solve for pKa first.

$pKa+pKb=14$

These other equations may come in handy as well:

$pKa=-log(Ka)$

$pKb=-log(Kb)$

$Kw=(Ka)(Kb)=1x10^{-14}$