Question

Consider the following data on some weak acids and weak bases K acid name nitrous acid is acid formula HNO, 45 x 10+ base K name formula hydroxylamine HONH, 1.1 x 10 aniline C6H,NH, 4,3 x 10-10 | hydrocyanic acid HCN 4.9 x 10-10 Use this data to rank the following solutions in order of increasing pH. In other words, select a 'l' next to the solution that will have the lowest pH, a '2' next to the solution that will have the next lowest pH, and so on. solution 0.1 M KNO choose 0.1 M CoMztjar choose one 0.1 KBr choose one 0.1 M NaCN choose one

Answer 1

The question involves the analysis of salt hydrolysis reaction. The salt hydrolysis reaction is backward acid base titration and one important concept involved in this question is relation between Ka,Kb and Kw .

Solution pH of o.lM KNO₂ The reaction for INO₂ is 1 No t'ho - HNO + oH The equilibrium constant of the reaction a is k = [Hng] [ok] [NO, Writing ICE table HNO₂ + oH - Initial change Egallibrium NO₂ + 4₂01 Ol O -X Corn x x But - CO.L-1) x <<0.1, because the kno, is - o salt of weak aced the degree of dissociation of ions ; very less so ko can be written as ko= x² 01 We know Kaxko = kw and ka for KINO ý 65x10 k=tw - Ka 2.22 x 10 4.5x10-4

- Y x = 2.22 x 10-11 x= 1.4gx10-6 [or] = 1.4gxto i.e. - pon of reach = -log (1.49. X 100) = 5.927 OH = 14-5.827 = 8.173 - 2 - ph of olm C H₂NH₂ Brian Reaction is - CH - NH + +Ho ç Initial ou Change Eawili 0.1-1 H₃NH₂ + Hi axa koz x I 0.1-0 Х<О. because C HANH is a weak base and canno degree of dissociation is very less. 0.1 kako ka= lol of Cath-NH = 4.3x10-10 43x10-10 from x² kaxol 2 2.325X10 = 2.325 x 10-6 1:52U X10 - Tim

oH 2 -log[144] = -log (1.024x104 2.817 3 0.1 m kor A Br is the salt of strong acid he and strong basc con this it - a neutral seelt i.e. pH = 7 u) 0.IM NOCN HUNN Initia] Equilibrium + Holl) 0. oi-n. HCN tor 0 0 - 0.1 . We know for hydrolysis reaction of salts kar kha kw ka of HCN = 4.9x1810 4.9810-10 = for ko = 2:04 x 105 x²= koxoil 12 = 2:04 X10-6 = x2 -1.428x 10-3 por 2 - log Tor] -log (1.43X103) 2.48

pH = 14-pon reaction is 2.48 0Hz 14-2.48 104 = 11.15 from the soln - we get the order of ph as 7 0 lm Cc H, NH Br <0.1M KBr <Olmkną COIMINACN,