Question

Question 6: (1 point) Selenous acid, H2SO3, is a diprotic acid with pKa,1 = 2.64 and pKa,2 = 8.26 at 25 °C. For 0.169 mol L-1 H2SeO3(aq) at 25 °C, calculate: (a) the fraction, at, of H2SeO3 that exists in the singly-ionized form, HSEO3- ay = (Enter a number between 0 and 1, accurate to 2 significant figures.) (b) the equilibrium concentration of the doubly-ionized form, Se032- [SeO32-leq = _ (Enter a number accurate to 2 significant figures.) mol L-1 (c) the pH pH = (Enter a number accurate to 2 decimal places.)

Answer 1

Comment in case of any doubt.

(a) pką, = 2064 = -log ka, => Kay = jāziny pkaz = 8.26 = -log kay => kay = 108:26 o 2 karc kaj so second dissociation of H₂ Se Oz will be negligible and can be ignored for Hot calculation. ICE kyselly 10g) + H0104 Hse O, 102) + H2O+108), Ka, = 10264 I: 0.169 o 116264kq=chgew] 4 C: -01 701 ItseO] Ei (0.169-81) 0:169-2 > >= 1396.169-70) =) 01? +0.00229101 -0.0003872=0 T = 0.0003872 => 71= -0.002291 + .0022912+4x0.0003872 -0.00229102 0 - . i tol a 3 10264 coucou 1 .7 = 0.01856 M= [ HSe 052] = [ Hzot] Q = [H5802] = 0.01856 = 0.1098 ~ 10.11 CHe se lydinitial 6.169 (b) H Se Og (aq) + H2OH) = Secosi car} + H2Ot (29), Ko= 109.25 178.26 [se 03-1C H205] [S20,93 40.01856) => [S& 0,)=(5.5x0% ZH Se Og ] | -9 5.49 5X10 10.01856) pH = log [ 430+] = -boy /0.01856) = (1173