Buffers are solutions of acid and base which work to minimise changes in pH following the addition of small amounts of acid or base. Ideal buffers are made of a weak acid (i.e. one which does not fully dissociate in water), and its conjugate salt (which will fully dissociate in water). Take, for example, the weak acid CH3COO-H+ and its salt CH3COO-Na+. The equation for the dissociation of ethanoic acid is: CH3COO-H+ <--> CH3COO- + H+ And since this is a weak acid, the equilibrium lies well to the left. When the salt is added, it fully dissociates, adding a lot of CH3COO- , which by Le Chetalier's principle shifts the equilibrium even further to the left. Upon the addition of acid, the concentration of H+ ions increases, and equlibrium is shifted even further to the left. Upon the addition of an alkali, the OH- ions react with the H+ ions present in the buffer. [H+] drops, and the equilibrium shifts to the right to replace them. Thus, when small amounts of either alkali or acid are added, the buffer minimizes any changes in pH.