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Wize University Chemistry Textbook > Buffers and Titrations

Buffer Range Problems

Foming BuffersPrevious Section
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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 πŸ’‘ 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:
CH3COOH  + OHβˆ’ β†’ CH3COOβˆ’ + H2O 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!

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

pKa Β±1\boxed{pKa\ \pm 1}

Example:
What is the effective buffer range for a buffer that has a pKa of 2?
pKa+1=2+1=3
pKa-1=2-1=1
Therefore, between pH=1 and pH=3, this buffer will have the capacity to act as a buffer!

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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=14pKa+pKb=14

These other equations may come in handy as well:

pKa=βˆ’log(Ka)pKa=-log(Ka)

pKb=βˆ’log(Kb)pKb=-log(Kb)

Kw=(Ka)(Kb)=1x10βˆ’14Kw=(Ka)(Kb)=1x10^{-14}



Practice: Buffer Range

If we are told that the Kb for the base in our base buffer is 6.3x10-5 what is the buffer range? (ans in pH)
Extra Practice
Practice: Buffers/Titrations
Buffers and Titrations - Long Answer Practice Problem
A student prepares a buffer solution in the lab by titrating bleach (sodium hypochlorite, NaCβ„“O) with HCβ„“ until they produce a 1:1 buffer. Ka for HClO = 3.5 x 10-8.
a. What is the pH of their buffer solution?
Buffer
If we are told that the Kb for the base in our base buffer is 6.3x10-5 what is the buffer range? (ans in pH)
Consider the following diagrams representing different buffer solutions:
Which of these buffer solutions has the highest acid AND base buffer capacities?
Comparatively how many moles of strong acid or strong base can we add a NaHCO3 / Na2CO3 buffer with a pH of 9.85 before the buffer capacity will be exceeded? Ka of HCO3- = 4.8Γ—10-11
Buffer Solutions
Consider the following diagrams representing different buffer solutions:
Which of these buffer solutions has the highest acid AND base buffer capacities?
Buffers/Titrations
A student prepares a buffer solution in the lab by titrating bleach (sodium hypochlorite, NaCβ„“O) with HCl until they produce a 1:1 buffer. Ka for HClO = 3.5 x 10-8.