Question

Smallers 23) (15 pts.) A saturated solution of zinc hydrokide is prepared at 25°C. Calculate, then compare the S molar solubility (least soluble to most soluble) of Zn(OH)2 in each of the following systems: a) in ost east b) in 7.5 x 103 M NaOH solution c) in 3.0 M NH3 (colorless complex ion Zn(NH3)42 forms) pure water wmmonion Lomwan on

Answer 1

Zn(OH) is least soluble in 7.5x153m solution This is due to common ion ettect of hydrouide im. since the amount of 04- in broduct side increases so according to Lechattier principal equilibrium shift towards left. so solubility decreases en cou)ą is most stable in ammonia solution. The increased Solubility is due to the formation of a soluble complex TZNNH3)4]?*. Ksp of Zn(OH)2 = 1.8x10-17 9 in pure water Encolla = En 2+ ( ap.) +204 (Op.) s 25 Ksp = [2n2t] [on]² = [s] (251² 1.8 x 10-19 453 1.8x10.17 = 63 310.45X10-17 Es Solubiling = 7.65810-6

solubility in 7.5 x103 m Nach Encong = ent rap.) + 204 Capi) 25 +4.5*10-3 ksp= [2n?"] [on]2 = (s') ( 85'+7:5416-3) 21<27.5x103 megketes' 1-8810-17 - [5') (7.5x154)? s 1.8x10-17 = 7.5 x 10-32 Is = 3.2x10-15 m 3.0M NHS Encou),(s) = 2n4tlap.) + 204 (af) 1. ksp = [2n2t] [on]² 10 1.64x10 an? (ap.) + 4NH3 = Kstal = 3-42 2x - Rstab = [an (Nm3)4] 2+ [znet] [Nu3] zn (on), ca) +4N13 = (20 ( NH3)4)* +201- 3-42 2 2x kep. - [zn (Nng)%]** Cona) [Nm]4 - [znzt) (zn (N145)43"com] [119379 [20]

kep. = Ksp x Ks tab. x is molar solubility a zn10h), in 3m Nha sol then at equilibrium Tell [Nhy] = 3-42 [on-]=2x [ 2n ( 10h324] 21 22 x kep. = (01) (201² (3-42)4 since (42621) 1.8xto kes. = 425 = ksp x K state 17 10 = 18X0 X 1.64 X10 423 = ).8 x16-17 X1:64x1010 X3 so x = 0.0060 x = 60x10 3 M in water s= 1.65x10-6 M in noon s= 3.2x10-13M least soluble in Nh3 s= 6.0x10 3 M most soluble