Buffer solutions

Conjugate Acid and Base Conjugate acid and base, HA/A-, differ by one proton. The conjugate acid of a base, is the base plus the attached proton. And the conjugate base of an acid is the acid minus the proton. Example:

Acid And Base Ionization Constants weak acid:CH3COOH + H2O ↔ H3O+ + CH3COO- [H3O+][CH3COO-] Acid ionization constant: Ka= [CH3COOH] weak base:NH3 + H2O ↔ NH4+ + OH- [NH4+][OH-] Base ionization constant: Kb= [NH3] Acid and base ionization constants are the measure of the strengths of acids and bases.

pK a and pK b pK a = -logK a pK b = -logK b larger K a → smaller pK a → stronger acid larger K b → smaller pK b → stronger base

Henderson-Hasselbalch Equation [conjugate base] [conjugate base] pH = pK a + log pH = pK a + log [weak acid] [weak acid] If: [weak acid] = [conjugate base], then: pH = pK a then: pH = pK a

Buffers A buffer is a solution characterised by the ability to resist changes in pH when limited amounts of acid or base are added to it. Buffers contain either a weak acid and its conjugate base or a weak base and its conjugate acid. Thus, a buffer solution contains both an acid species and a base species in equilibrium.

Example of weak acid/conjugate base as buffer system: HC 2 H 3 O 2 + C 2 H 3 O 2 - How does this work? What happens when H + is added? What happens when OH - is added?

How A Buffer Solution Works The acid component of the buffer can neutralize small added amounts of OH -, and the basic component can neutralize small added amounts of H 3 O +. The acid component of the buffer can neutralize small added amounts of OH -, and the basic component can neutralize small added amounts of H 3 O +. The result is just more weak acid or more weak base in the system. The result is just more weak acid or more weak base in the system.

Acetic Acid/Acetate Buffer

Buffer resist change in pH

Buffer Capacity And Buffer Range There is a limit to the capacity of a buffer solution to neutralize added acid or base, and this limit is reached before all of one of the buffer components has been consumed. There is a limit to the capacity of a buffer solution to neutralize added acid or base, and this limit is reached before all of one of the buffer components has been consumed. In general, the more concentrated the buffer components in a solution, the more added acid or base the solution can neutralize. In general, the more concentrated the buffer components in a solution, the more added acid or base the solution can neutralize. As a rule, a buffer is most effective if the concentrations of the buffer acid and its conjugate base are equal. As a rule, a buffer is most effective if the concentrations of the buffer acid and its conjugate base are equal. Buffers are effective around pH values that are equal to the pKa ±1. Buffers are effective around pH values that are equal to the pKa ±1.

Power of Buffering Action

summary: Buffers consist of Weak acid and its salt Weak base and its salt or and resist changes in pH to Maintain pH balance preventing AcidosisandAlkalosis

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