Question

Consider a solution that is 2.4×10⁻² M in Fe2+ and 1.8×10⁻² M in Mg2+.

[K2CO3] = 1.3×10⁻⁹ M is the minimum concentration of K2CO3 is required to cause the precipitation of the cation that precipitates first

What is the remaining concentration of the cation that precipitates first, when the other cation just begins to precipitate?

What is the remaining concentration of the cation that precipitates first, when the other cation just begins to precipitate? Express your answer using two significant figures. 60 ALQ * O O ? [Fe2+] = M Submit Previous Answers Request Answer X Incorrect; Try Again; 3 attempts remaining

Answer 1

Ans :-

Partial dissociation of MgCO₃ is :

MgCO₃ (s) <------------> Mg²⁺ (aq) + CO₃^2- (aq)

Expression of solubility product (K_sp) is :
K_sp = [Mg²⁺].[CO₃^2-]

6.82 x 10^-6 M² = (1.8 x 10^-2 M). [CO₃^2-]

[CO₃^2-] = 6.82 x 10^-6 M² / (1.8 x 10^-2 M)

[CO₃^2-] = 3.79 x 10^-4 M

Also,

Partial dissociation of FeCO₃ is :

FeCO₃ (s) <------------> Fe²⁺ (aq) + CO₃^2- (aq)

Expression of solubility product (K_sp) is :

K_sp = [Fe²⁺][CO₃^2-]

3.07 x 10^-11 M² = [Fe²⁺].(3.79 x 10^-4 M)

So,

[Fe²⁺] = 3.07 x 10^-11 M² / (3.79 x 10^-4 M)

[Fe²⁺] = 8.1 x 10^-8 M

Hence, [Fe2+] = 8.1 x 10-8 M ​​​​​​​