Consider the following data showing complex ions in aqueous solution and their K

Question

Consider the following data showing complex ions in aqueous solution and their K f values. (Picture attached of entire problem)

Consider the following data showing complex ions in aqueous solution and their K_f values. Based on this data, which of the following is correct? ZnCO_3 will be more soluble in NH_3 than pure water. Zn(CN)_2 will precipitate if NaCN is added to a solution containing Zn^2+ (aq). Zn(OH)_2 is more soluble at lower pHs than higher pHs. CN^- is a weaker Lewis base than water. A, C, D a, b, C A a, b, C, D

Explanation / Answer

answer : A , B , C

explanation:

1) Zn (NH3)4+2 formation constant is very high that os 2.8 x 10^9 so Zn+2 very rapidy react with NH3 form Zn (NH3)4+2 so more soluble in NH3

2)   Zn+2 + 2CN -   -----------------> Zn(CN)2 (s)

   if excess CN- added complex is fromed

3)

Zn (OH)2 --------------> Zn+2 + 2OH-

Ksp = [Zn+2] [OH-]^2

3 x 10^-17 = (S ) [OH-]^2

if pH is low pOH is high than [OH-] is low so S value is more

suppose : at pH = 5 , pOH = 9

[OH-] = 10^-9

S = 30 M

suppose at pH = 6 , pOH = 8

[OH-] = 10^-8

S = 0.3

pH increase S value decreases. so the above statement is correct

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