12.4 Titrations and Buffers

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Titrations

A titration involves the neutralization of an acid by a base or a base by an acid.
Titrations are often used to quantitatively determine the concentration of acid or base present in a sample.
The acid or base of unknown concentration is referred to as the analyte.
The acid or base of known concentration you are titrating the analyte with is referred to as the titrant.
The titrant is typically added using a precise volumetric piece of glassware called a buret.
When the analyte is completely neutralized the titration has reached the equivalence point.
A color-changing indicator is often used to determine when the equivalence point has been reached.

titration of hcl
buret

If 36.2mL of 0.10M NaOH was required to reach the equivalence point in the titration of 50.0mL of HCl, what was the concentration of the HCl?

Buffers

A buffer is a solution that resists changes in pH. It is composed of a weak acid / conjugate base pair.
A buffer is only effective over a small pH range characterized by the pKa of the weak acid (pKa ± 1).
High concentrations of the components and a pH closer to the pKa result in a higher buffering capacity.

Preparing a Buffer
Weak Acid / Conj. Base
1      :      1
Weak Acid / Strong Base
2      :      1
Weak Base / Strong Acid
2      :      1

Which acid along with its conjugate base would make the best buffer of pH 5.0?

Acid pKa
HF 3.2
HC2H3O2 4.7
H2CO3 6.4
HCN 9.2

Which of the following would make a buffer with the highest buffering capacity?

a) 0.1M HF / 0.01M NaF
b) 0.2M HF / 0.1M NaF
c) 0.67M HF / 0.65M NaF
d) 0.7M HF / 0.01M NaF