Question

a) Calculate the pH of a 0.8M solution of HCOOH (K_a = 1.8 x 10^-4) in 0.4M Li⁺ HCOO^-.

b) Calculate the pH of a solution of 0.4M NH₄Cl and 0.5M NH₃ (pKa NH₄⁺ = 9.2).

c) Calculate the pH of a titration of 100 mL 1.5M HCl when 75 mL 1.25M NaOH has been added.

d) What volume of 1.25M NaOH must be added to 100 mL of 1.5M HCl to reach equivalence?

Answer 1

a) HCOOH + 2H Cooli mixture forms a buffer. (Audic buffer) pH of buffer solution i given by pH = pka + log (Salt) plat og fer than Given that K 4 HCOOH = 1.8X1079 [HCOOH) = 0.8 M [Lit Hool= 0.4 moi a = -log ka = -log 8.8x1074) a logies-logloy halog 1.8. = 3.745 p. 3.745+ 10504) 3.545 + logis) - 3.745+ logos 3.44 61 The mintuse of NH3 L NH4Cl forms basic butter. Pot of basic buffer is given by kian OH - P + log (P [Salt)

Given that (NH3) = 0.5M PnHuel] = 0.4M pke of NHY = 9.2 pka = -log Ka M -962 log Kai -9.2 6.31810 10 = 6.31x10-10 1 .Kor 10 The relation between Ka Z. Ko s givenly Ka Kb = kwa Ke Toxinly : 6:31X18 to min 0.1585x10 4 = 1.585x105 , CNH, cH E-log Kg Ilog [when (NA) -log (1.585x103) thg = -log(1585) – logio + log|818) 5-log 1.585 I lo scors) = 4.7 E

lince Phot pot = 14 M M B = 14,004 =14-yit -9.31 c) when v ml of My acid is mixed with Vg ml of Me dbane, the concentration of Solution is given by resultant M M , V, _Mz Vz, it MV SMUL & S017 Aledic vitven MV SMN, ES in _Mz Vz-MV, basic Given ! Hd 3, INCOH My = 1.25 M=15 N-7802 V = 100 ml 100x1.5-7521:25 z 3 100+75 M. Since MANYHOP L Macon Nach i Solution acidis? 0.321 M I E -log (W) = -log(0.321) = 0.49 20.5

During a titration, the eiluhen formule is MV = M V2 Ho, te n ne 10 Na oH THU - Nad to Hy : NaOH M: Molarity rivoluze M = 1.5M N = no of " more , M = 1.250 V,=? n = 1 Vz-room =1 NDV=he Bum My Vzymy 1:5X100 % lies 150 (20 mL. = 1,25