Mastering Chemistry Help

The pH of acidic and basic buffer can be calculated by Henderson – Hasselbalch equations. Consider an acidic buffer HA + A - HA H + + A - K a = [H + ] [A - ] / [HA] [H + ] = K a [HA]/[A - ] [H + ] = K a [acid]/[salt] There fore pH = -log[H + ] pH = pK a + log [salt]/[acid] when, [salt]/[acid] = 1 , pH = pK a Since pK a of an acid is a constant at constant temperature, the pH of the buffer is constant. Thus buffer capacity is maximum in a solution containing equivalent amount of acid and its salt. The pH of basic buffer is also given by Henderson – Hasselbalch equation BOH B + + OH - K b = [B + ][OH - ]/[BOH] [OH - ] = K b [BOH]/[B + ] pOH = pK b + log [salt]/[base] pH = 14 – pOH = 14 – [pK b + log [salt]/[base]]

The property of a buffer solution to resist change in its pH value even when small amounts of the acid or the base are added to it is called buffer action . Consider the acidic buffer solution containing acetic acid and sodium acetate. They dissociate as CH3COONa <=======> CH3COO - + H + CH3COONa <=======> CH3COO - + Na + When a few drops of an acid, HCl is added to this buffer solution, the H + ions combine with CH3COO - ions to form weakly ionized molecules of CH3COOH. CH3COO - + H + <=======> CH3COOH Thus H + ion concentration does not change and hence the pH of the solution remains constant. When a few drops of base, NaOH is added to the buffer solution, hydroxyl ions of the base neutralize the acid, forming salt and water. Similarly, in a basic buffer solution of NH4OH and NH4Cl, they dissociates as NH4OH <======> NH4 + + OH - NH4Cl ----------> NH4 + + Cl - When a few drops of a base added, the OH - ions given by it combine with NH4 + ions to ...

Maintenance of PH in blood and in intracellular fluids is absolutely crucial to the processes that occur in living organisms. This is primarily because the functioning of enzymes is sharply pH dependent. The normal pH value of blood plasma is 7.4 and several illness or death can result from sustained variations of a few tenths of pH unit. Also many medical and cosmetic formulations require that these must be kept and administered at a particular pH. There are solutions which resist the change in pH on addition of small amount of acid or alkali and are called Buffer solution . For example a mixture of H 2 CO 3 and HCO 3 - is a natural buffer system which maintains the pH of blood. A buffer that is widely used in clinical laboratory and in biochemical studies in the physiological pH range is prepared from tris amino methane (hydroxy methyl) (THAM) [(HOCH 2 )3CNH 2 ]. In order for a solution to act as a buffer it must have two components, one of which is able to neutralize acid and the o...