Buffer & buffer equations

Buffers & buffers equation ( Acidic & basic Buffers)

1. BUFFER & BUFFER EQUATIONS NIDHI SHARMA

2. INTRODUCTION- A  Buffer  is a solution that can resist pH change upon the addition of an acidic or basic components. It is able to neutralize small amounts of added acid or base, thus maintaining the pH of the solution relatively stable.

3. TYPE OF BUFFERS- Buffers are of two types- 1. Acidic buffers- These are the solutions that have a pH below 7 and contain a weak acid and one of its salts. E.g .- A mixture of acetic acid (CH3COOH) and sodium acetate (CH3COONa) acts as a buffer solution with a pH of about 4.75. 2. Alkaline buffers- These are the solution that have a pH above 7 and contain a weak base and one of its salts. E.g.- A mixture of ammonium chloride (NH4Cl) and ammonium hydroxide (NH4OH) acts as a buffer solution with a pH of about 9.25.

4. BUFFER EQUATION- Buffer equation for Acidic buffers- CH3COOH CH3COO- + H + CH3COONa CH3COO- + Na + We can also write it like this- HA H + + A- BA B + + A- Ka = [H + ][A-]/[HA]

5. [H + ] = K a [HA]/[BA] = K [HA]/[BA] Taking negative logarithms of both sides of the above equation gives- -log ([H + ]) = -log (K a ) – log ([HA]/[BA]) or pH = pK a – log ([HA]/[BA]) It can also be written as- pH = pK a + log ([BA]/[HA]) This form of the ionization or dissociation constant expression is called the Henderson-Hasselbalch equation.

6. Buffer equation for Basic buffers- NH4OH NH4+ + OH- NH4Cl NH4+ + Cl- We can also write it like this- BOH B + + OH- BA B + + A- Kb = [OH-][B+]/[BOH] [OH- ] = K b [BOH]/[B+] = K [BOH]/[BA] Taking negative logarithms of both sides of the above equation gives-

7. -log ([OH-]) = -log (K b ) – log ([BOH]/[BA]) or pH = pK a – log ([BOH]/[BA]) It can also be written as- pH = pK b + log ([BOH]/[BA]) This form of the ionization or dissociation constant expression is called the Henderson-Hasselbalch equation.

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