Question

Consider Figure 14.5. For each curve the concentration of acid and base are the same, e.g., the curve labeled 1 M is for the titration of 5 drops of 1 M weak acid with 1 M NaOH. Why are the titration curves for the different reagent concentrations so similar in the buffer region? Are these solutions all buffers? Explain. 1 2

Answer 1

(srmy base Titratfan af Weqk acid vý NaOH For each curve comcentratfon at acid and base are the same We have 5 drops of Atid ets say1drop = 1 mL S0,5drup 5mL SoTihralfan af 5mL x M weak actd with * M NaoH solutton is done ; x is varying Tihra bton curve for different reggen con centration s Naoltso Simílar in the bufter reaim - The cause af this effect dis cussed below M IKIO 2M XI0M Buffer region PH Halt equtalance point Equivalan ce point Drops at added Nao1H At starting when no base is added, PH of the Solutim depends upon the concentration of acid solutfm A tho sa weas acid hus formula ot PH iJ- ÞH- Pkalg facid] kadssuation constant of ueak acid

At the buffer regtun pit is Calculated by using the fomula [Solt acid PH Pka la pka t5 canstant for same acid soluttoY so the pH TS my depends m the ratto of Sal t/Lacia Fa 1 M Soluti CSalt Lacid salt Cacid Base added 4mL 6 mL 1 mL 6mL e have, 5mL 1M) weaK acīd we added Iml 1M Base Solutfon, now, total volume - 6 mL as 1mL acid neutralled by ImL base 4mL х 1м) mL х1и) 6 mL Ssalt for med atter adding Im base M e 01 M soutim Salt Eacidi 5alt Lacid Base added mL -x0-1 (M) 4mL -хо1 6mL 1mL 6mL Sn the Same way ue can calculate the ratio of Salt Lacidi Solution alSO For other different concentratton

Atter calculating we seen that Sal]/tacid] Yatio is not changed for difterent cancenta tim soluton Hence fra fixeed volume of base added (lets say mL) the vatio ot [Salt ffned for difterent cancentratian solutim Tacid A3Esau Lacid Yemains same for au difterent concen hatfon Soution at the bufter re gion - is not change thus pH is also For this reason the titratim curve for difteren Yeagent concentratfon so similay at buffer Yegim when a Smull amount af base added to the eweak acid soluttom it furms salt and water The mixture ot weak actd and its saltis formed which act as a buffer soluton > Na A + H20 (Salty HA Na 0H acid Buffer solutfon comsists at wrak acid / weak base cand its salt MHA and Afut Na A X M) HA and x (^) Na A Solultm act as a butter solutfn These au soluttims are acid - base mixture, these Colutims Cannot ast as buffer because buffer Solutim contains only weak acid HA) and its saltaa)