1. Buffer Solution Presentation.

2. Why do we need a buffer?
If we added mol of NaOH to 1.00 L of pure water the change in pH would be from 7.00 to 12.78
pH of M NaOH
[OH–] = M
pOH = –log(0.060) = 1.22
pH = – 1.22 = 12.78
pH = – 7.00 = 5.78
An enormous difference!
Buffers prevent wide swings in pH unless a huge excess of strong acid or base are added

3. Buffer Solution
A solution that resists a change in its pH when small quantities of a strong acid or a strong base are added to it.
Made up of two solutes: a weak acid and its conjugate base
CH3COOH and CH3COO– (CH3COONa)
NH4+ (NH4Cl ) and NH3

4. How a Buffer Works
Consider acetic acid HA and its conjugate base acetate A– present in same solution in significant amounts
If we add a strong acid, it reacts with the conjugate base
H+(aq) A –(aq)  HA (aq)
Thus preventing a buildup of H+
If we add a strong base, it reacts with the conjugate acid
OH–(aq) + HA (aq)  A –(aq) + H2O
Thus preventing a buildup of OH–

5. pH of a Buffer Solution
pH of a buffer solution containing M acetic acid (Ka = 1.8 × 10–5) and M sodium acetate.
HA(aq) <=> A–(aq) + H+(aq)
Ka = [A-][H+]
[HA]
Henderson – Hasselbach equation
pH = pKa + log [A-]

6. pH of a Buffer Solution
We can use initial concentrations of both weak acid and conjugate base as equilibrium concentrations
pH = log 0.450M
0.650M
pH = 4.58
The pH of a buffer is determined by only the ratio of
[A-]/[HA]. A buffer solution containing 0.065M acetic acid and 0.045M sodium acetate would have the same pH, but buffer efficiency is smaller.

7. Buffer Capacity: β=B /pH
Let us consider the change of the pH after addition of mol of NaOH to 1L of buffer solution 0.650M HA and 0.450M NaA
Acetic acid neutralizes added strong base NaOH
HA(aq) + OH–(aq)  A–(aq) + H2O
pH = log ( )M = 4.68
(0.650 – 0.060)M
pH has changed by only 4.68 – 4.58 = 0.10 unit
Buffer capacity: mol of added base/ change in pH β=B /pH = (0.060 mol )/ (0.10 pH unit) = mol/pH

8. Effect of Dilution on Buffer Capacity
What is the pH after addition of mol of NaOH to 1L of buffer solution 0.065M HA and 0.045M NaA
HA(aq) + OH–(aq)  A–(aq) + H2O
pH = log ( )M = 4.68
(0.065 – 0.006)M
pH has changed by 4.68 – 4.58 = 0.1 unit
Buffer capacity has decreased 10 times after dilution β=B /pH = (0.006 mol )/ (0.10 pH unit) = 0.06 mol/pH

9. Buffer Capacity Buffer capacity is expressed as the amount of strong
base (acid) that must be added to 1 liter of the solution to
change its pH by one unit.
The buffer capacity depends essentially on 2 factors:
Ratio of the acid and its conjugated base. The buffer
capacity is optimal when the ratio is 1:1; that is, when
pH = pKa
Total buffer concentration. For example, it will take more
acid or base to deplete a 0.5 M buffer than a 0.05 M buffer.

10. Buffer Capacity
The relationship between buffer capacity and buffer concentrations is given by the Van Slyke equation:
β=2.303 x C x Ka x [H3O+]
(Ka + [H3O+])2
where C = the total buffer concentration (i.e. the sum of the molar concentrations of acid and its conjugated base).
The maximum buffer capacity occurs when pH = pKa

11. Effectiveness of a Buffer
The buffer effectiveness refers to the maximum amount of either strong acid or strong base that can be added before a significant change in the pH will occur. The maximum amount of base that can be added is equal to the amount of weak acid present in the buffer. The maximum amount of strong acid that can be added is equal to the amount of conjugate base present in the buffer

12. Importance of Buffers
The concepts of buffer and buffer capacity appear in varied disciplines, including analytical chemistry, and environmental chemistry, biology, physiology, medicine, dentistry, and agriculture.
For example buffer in blood: HCO3– and H2CO3
Absorb acids and bases produced by metabolism
Maintains a remarkably constant pH (7.4)

13. Buffers Important as cells live only in a very narrow pH range.
A decrease of blood pH is called acidosis, an increase is called alkalosis.
Respiratory and metabolic disorders occur when the body’s acid-base is out of balance. One of the treatments for an acid-base imbalance involves intravenously injecting sodium lactate to restore acid balance and electrolytes to the body.

14. Thank you.