Question

Write the net ionic equation for the acid-base hydrolysis equilibrium that is established when potassium cyanide is dissolved in water. + H2O(l) = This solution is Submit Answer Retry Entire Group 8 more group attempts remaining

Answer 1

1. KCN (aq) -----> K+ (aq) + CN- (aq)

Here K+ is neutral and CN- is basic

so the net equation is

CN- (aq) + H2O (l) --------> HCN (aq) + OH- (aq)

2. NH4ClO4 produce NH4+ and ClO4 - ions

where NH4+ is acidic , ClO4- is neutral

we have to find pH for NH4+

Given initial concnetration of NH4+ 0.200 M NH4+ isa weak acid can be dissociate as below in aq. Solution НЗО+ (аq) NH3 (aq) NH4+(aq)H20 (I) + Initial 0.2 0 0 ( +x) (x) ( +x ) Change (-х) (0.20-x) Equilibrium (х) Given Kb of NH3 = 1.8 x 10^-5 ; but Ka x Kb = Kw = 1.0 x 10^-14 Then Ka Kw / Kb = 1.0 x 10^-14/1.8 x 10^-5 = 5.55 x 10^-10 weak dissociation constant Kacan be expressed as below [NH3] [H30+ [NH4+ ] (х) (х) Ка asume x is small then 5.555E-10 0.2000 (0.20-x) will be 5.555E-10 x^2 0.2000 0.2000 So X^2 5.555E-10 0.2000 x^2 1.111E-10 SO 1.054E-05 х but from ICE table x = [H3O+] so [H3О+]- 1.05E-05 but pH -log H30+] = -log [ 1.05E-05 ] 4.977 4.98 so pH of NH4+ solution = pH is <7 so the solution is acidic