Question

PH. OF of pH 5.00. Acetic decrease in pH? What Example 6. (a) It is desired to prepare 100 ml of a buffer of pH 5.00 benzoic, and formic acids and their salts are available for use. Which aria be used for maximum effectiveness against increase or decrease in acid-salt ratio should be used? The pk, values of these acids are: acetic, 4.74; benzoic, 4.18; and form The pK, of acetic is closest to the desired pH, and this acid and its salt she used. Then [HOÀc] pH = pka - log foAc ] [HOÀc] 5.00 = 4.74 - log ToAc] Taking antilogs, [HOAc]/[OAC] = 1/1.8, or the salt-acid ratio should be 1.8.1. This is the molar ratio, not the ratio of grams. (b) If it is desired that the change in pH of the buffer be no more than 0.10 unit for the addition of 1 mmol of either acid or base, what minimum concentrations of the acid and salt should be used? Since there is less acid present than salt, a greater change in pH will result if base is added. Hence if we calculate on the basis that base is added, the condition will be more than satisfied for the addition of acid. Thus, if x = mmol acid originally present 1.8x = mmol salt originally present If 1 mmol OH is added, then x-1 = mmol acid remaining 1.8x = mmol salt Chapter 6

how it is solved that problem, there it is the answer, but I tried many steps and I cant get that results. please provide step by step. thank you

Answer 1

AcOH + ou - AO + H₂O on addition of base, ph would x 1 1.82 increases, pr-5.00 +0.10 = 5.10 t- newequili. x.) - 1.8x+1 5.10=4.74 + log (Aco] (Aon] log('184) - S-10-4.74= 0.36 1+1.8* = 10 = 2.291 → 1+1'8x = 2:2911-21291 3.291 - (2.291-18)* = x= 3.291. 0.491 2= 6.7 mmol, 18n=1.876.7 = 12:06 mmol. X -) 0.36 6-7 mmol 100mL = 0.067 md / 12.06 mmol 100 ML -0.121 mol/L