Question

A solution contains 6.16×10^-3 M potassium bromide and 1.32×10^-2 M sodium hydroxide.
Solid silver acetate is added slowly to this mixture.

A. What is the formula of the substance that precipitates first?

B. What is the concentration of silver ion when this precipitation first begins?
[Ag⁺] =  

Answer 1

A)

Concentration of Potassium bromide = 6.16 x10^-3M

Concentration of hydroxide = 1.32 x10^-2M

after addition of silver acetate

KBr(aq) + CH3COOAg(s) ---------------------- AgBr(s) + CH3COOK(aq)

NaOH(aq) + CH3COOAg(s) ---------------------- AgOH(s) + CH3COONa(aq)

Ksp of AgBr = 7.7x10^-13

Ksp of AgOH = 2.0x10^-8

Ksp of AgBr is less than Ksp of AgOH

SO, AgBr is prepititated first.

Hence, the formula of first precipitate = AgBr

B)

Ksp of AgBr = 7.7x10^-13

Concentration of Br- = 6.16x10^-3M

AgBr(s) ------------------- Ag+(aq) + Br-(aq)

Ksp = [Ag+][Br-]

7.7x10^-13 = [Ag+] x 6.16x10^-3

[Ag+] = 1.25x10^-10M

Concentration of Ag+ = 1.25 x10^-10M