Question

In a weak acid when [HA]=[A-]the pH = the pKa. What is the pH after adding 0.50 moles HCl to a solution of HA =1 mole and A- = 1 mole. The pKa of the weak acid = 4

Answer 1

* - acidic Here we have an buffer of weak a cid. HA and its Conjugate Base HA - Htta Ka. (as) (a) lagi . Rua [ut] [A] CHA ] : Kax [HA ] [H] ( Takring log on both the side, we get [A ] logka + log (MA) = log[4] hogy ket - loy content - logcue = pH pka they are on PA, Handersen - Hasekboth equation. when CHAJ= [AO], pH = pka + log (7) opkatlog when 11 [phopka] (as log 2 =]

But now, in the equilibrium of HA/A" we have added He NHA = I mole } hots say the volume of Colution in 11 no- 1 mola Her = 015 Mola to, [HA] = [A] = 1M (Hal-0,5M HA 1.om - limiting [HT] = 0.5m. I reactant HA; + A, (kalo") 0.5M 1 1.09 - Addition of AL pka ay log ka = 4 =104) ta Cordeling lism 1.5m - o.SM at Product lison - Products it from . He will cause the reaction - to proceed in backward orth - nois direction by Le Chatelier's principle ) t= teq n ~15 Ka a [A] [HP) . CHAI nxois L2/04 Tis na istiot -> K210 10.52 Chego 103.52 pH = -log (H"]= -log 15352 1PH 23:52)