Buffer solution is a solution that resists changes in pH. Buffer solutions can occur either at acidic or basic pH. An acidic buffer solution consists of a solution of a weak acid and its conjugate base, for example ethanoic acid and sodium ethanoate. A basic buffer solution consists of a solution of a weak base and its conjugate acid, for example ammonia and ammonium chloride. If the added solution varies with the pH value of the original buffered solution, the pH of the final solution will remains unchanged, provided that the buffer is not full. Buffer solutions provides its buffering effect mainly based on the effect of chemical equilibrium. Buffer solutions is an essential kind of reagent in many biological processes involving living organisms as well as many modern chemical industrial processes.
Their composition.
Typically a buffer solution contains a weak acid and its conjugate weak base in approximately equal concentrations, with both components present in appreciable amount. For example, if we need to prepare a buffer solution in the laboratory, we can do so by mixing ammonium chloride (NH4Cl) and ammonia (NH3), provided that each component is of high concentration.
How they function.
To see how buffer solutions work, let us write the equilibrium expression for the ionization of a weak acid, HA. The equation for the ionization of a weak acid is.
HA(aq) + H2O(1) == H3O+(aq) + A-(aq).
To write the equilibrium expression, the concentration of the products, H3O+ and A-, are divided by the concentration of the reactants, HA and H2O, and set equal to Ka, the equilibrium constant.
[H3O+][A-] = Ka.
[HA][H2O] .
Rearranging this expression to solve for the H3O+ ions gives.
[H3O+] = Ka [HA][H2O][A-].
The concentration of the H3O+ ions depends on the ratio of the concentration of HA to A- or the weak acid and its conjugate base. For producing an effective buffer action is to keep both these concentrations equal and keep the concentrations fairly large.
