Question

can u help plZ?

A solution contains 6.26x10M potassium sulfide and 1.01x10-2 M ammonium carbonate Solid zinc acetate is added slowly to this mixture. A. What is the formula of the substance that precipitates first? formula = B. What is the concentration of zinc ion when this precipitation first begins? [Zn2+]= M Submit Answer Retry Entire Group 8 more group attempts remaining

Answer 1

1.Sol :-

(A). Reaction between K2S and (CH3COO)2Zn.

K2S (aq) + (CH3COO)2Zn (aq) ----> ZnS (s) + 2CH3COOK (aq)

and

Reaction between (NH4)2CO3 and (CH3COO)2Zn.

(NH4)2CO3 (aq) + (CH3COO)2Zn (aq) ----> ZnCO3 (s) + 2CH3COONH4 (aq)

Ksp of ZnS = 1 x 10-23

and

Ksp of ZnCO3 = 1.0 x 10-7

Because, Ksp of ZnS < Ksp of ZnCO3 , therefore ZnS will form precipitates first.

Hence, formula of the substance which precipitates firs is = ZnS

(B).

Partial dissociation of ZnS is :

ZnS (s) <--------------------> Zn2+ (aq) + S2- (aq)

Expression of Ksp is :

Ksp = [Zn2+].[S2-]

[Zn2+] = Ksp / [S2-]

= Ksp / [S2-]

= 1 x 10-23 M2/ 1.01 x 10-2 M

= 9.90 x 10-22 M

Hence, [Zn2+] = 9.90 x 10-22 M