Buffers

What 2 things are the pH of a buffer solution dependent on?

(1) The pKa of the weak acid (2) the ratio of the weak acid and its conjugate base.

What is a typical buffering range?

+/-1 pH unit. Example: Acetic Acid the pKa is 4.74. The buffering range is 3.74-5.74.

In a titration graph what are the labels for the x and y axis?

Y = pH X = mL 0.05 NaOH added ( or simply base added)

Are amino acids polprotic? How many titratable groups do they have?

Yes. Amino acids are polyprotic. They have a carboxylic acid (COOH) and an amine (NH3+). Some amino acids also have a third titratable group, as part of the R group. Therefore, the amino acids will all have two pKa values, and some will have three values. Notice that the R group pKa values can come between the carboxylic acid and amino groups, or after the amino group. Some pKa values are shown below.

What is the Henderson Hasselbach equation?

pH = pka + log (Conjugate base/Conjugate Acid)

What is happening when a buffer is resisting pH changes?

It is absorbing H+ and OH- ions.

What is the capacity of a buffer to resist significant changes in pH dependent on?

It is dependent upon both the concentration of the buffer and the difference in pH of the buffer compared to the pKa of the weak acid component. The Henderson-Hasselbalch equation may be used to calculate the final pH of a buffer after addition of a strong base or acid.

What is the definition of a buffer?

A solution of a weak acid (proton donor) and its conjugated base (proton acceptor) that resists significant changes in pH upon addtion of small quantites of strong acid or base.

What happens to polyprotic compounds during titrations and what does the graph look like?

Polyprotic compounds lose hydrogen ions in order according to pKa, and have multiple buffering regions in a titration graph.

What does polyprotic mean?

Polyprotic means the compound has multiple hydrogen ions which can be titrated.

Buffering range

The pH range where a buffer can effectively absorb or donate protons. This determines how much weak acid is available to donate protons to added base and how much weak base is availlable to accept protons from added acid.

Buffering capacity

The total molar amount of the weak acid and its conjugate base making up the buffer. This determines the number of H+ that can be absorbed or donated.

What are buffers? What do they do?

They are weak acid-base pairs. They maintain proper cellular pH.

What do buffered solutions do?

They resist changes in pH when an acid or base is added.

When is the pH equal to the pKa of the weak acid?

This happens when the concentration of the weak acid is equal to that of the conjugate base. These buffers are optimally buffered against both strong acids and strong bases.