2.1.3 Define, using examples, buffer, and explain how it works

Buffer solution

- It is a solution that resists the change in its pH upon the small addition of acid or base.

- Buffer resists the change pH because they have in the solution components acting as both acid and

base.

- The acid component neutralizes the added base and the base component neutralizes the added acid.

Buffers can be made by mixing:

1. Weak acid and its conjugate base (Acidic Buffer)

2. Weak base and its conjugate acid (Basic buffer)

3. Weak acid, in excess, with strong base

4. Weak base, in excess, with strong acid

2.1.4 Determine and explain the characteristics of the buffer

2.1.5 Differentiate between acidic and basic buffers

2.1.6 Calculate the pH of a buffer solution

2.1.7 Write the Henderson-Hasselbalch equation and explain how it is used to calculate ate pH

of a buffer

Henderson–Hasselbalch Equation

- The equation calculates the pH of a buffer from the pKa and initial concentrations of the weak acid

and salt of the conjugate base, as long as the “x is small” approximation is valid.

2.1.8 Explain, using Le Chatelier’s principle, the change in pH when a small amount of acid

or base is added to a buffer system

2.1.10 Identify factors that determine the effectiveness of a buffer

Buffer effectiveness:

1) A buffer becomes less effective as the difference in the relative amounts of acid and conjugate base

increases.

2) Effective buffer must have a [base]/[acid] ratio in the range of 0.10 to 10.

3) In order for a buffer to be reasonably effective, the relative concentrations of acid and conjugate base

should not differ more than a factor of 10.

4) The buffer with the greater amounts of acid and conjugate base is more resistant to pH changes and

thus a more effective buffer.

5) The more dilute the buffer components, the less effective the buffer.

2.1.11 Define buffer capacity

Buffering Capacity

- It represents the amount of acid (H+) or base (OH⁻) the buffer can absorb (neutralize) without significant change in pH

- A buffer with a large capacity contains large concentrations of buffering components and so can

absorb relatively large amounts of acid or base and shows a little change in pH.

- Dilution of a buffer has no effect on its pH.

- The capacity of a buffered solution is determined by the values of [Acid] and [Base]

2.1.12 Identify a range of a buffer and how it is determined

Buffer Range

- It is the pH range the buffer can be effective.

- The effective range is pKa ± 1

- When choosing an acid to make a buffer, choose one whose pKa is closest to the pH of the

buffer.

2.1.13 Calculate the range over which a buffer will be most effective

2.1.14 Define titration curve, equivalence point, and endpoint

- Titration is commonly used to determine the amount of acid or base in solution.

- In an acid–base titration, a solution of known concentration (titrant) is slowly added to a solution of

unknown concentration (analyte) from a burette until the reaction is complete.

- When the reaction is complete we have reached the endpoint of the titration.

- End point is the point in a titration at which the indicator changes color.

- An indicator is a chemical that changes color when the pH changes.

An indicator may be added to determine the endpoint.

- Equivalence point or Stoichiometric point

The point in a titration when enough titrant has been added to react exactly with the substance in

solution being titrated.

Equivalence point is defined by stoichiometry not pH

The equivalence point is so named because the number of moles of acid and base are

stoichiometrically equal at this point.

- pH Curve or Titration Curve

The progress of titration is represented by plotting the pH of the solution versus the volume of the

added titrant (whose concentration is not known)

2.1.15 Explain, using the particulate diagram, the process of titration

2.1.16 Explain the titration curve, and identify the important points on the curve for the titration

of strong acid and strong base, titration of a weak acid with a strong base, titration of a weak

base with strong acid, and titration of polyprotic acids