The solubility-product constants, Ksp, at 25 ?C for two compounds [iron(II) carb
ID: 957833 • Letter: T
Question
The solubility-product constants, Ksp, at 25 ?C for two compounds [iron(II) carbonate, FeCO3, and cadmium(II) carbonate, CdCO3] are given by the table Substance Ksp FeCO3 2.10×10?11 CdCO3 1.80×10?14 A solution of Na2CO3 is added dropwise to a solution that contains 1.24×10?2 M Fe2+ and 1.58×10?2 M Cd2+. What concentration of CO32? is need to initiate precipitation? Neglect any volume changes during the addition. Express your answer with the appropriate units.
Problem 14 Part A The solubility-product constants, Ksp, at 25 °C for two compounds [iron(lI) carbonate, FeCO and cadmium(I) carbonate, CdC03] are given by the table A solution of Na2CO3 is added dropwise to a solution that contains 1.24x10-2 M Fe2+ and 1.58 10-2 M Cd2. What concentration of CO3 isneed to initiate precipitation? Neglect any volume changes during the addition. Express your answer with the appropriate units. Substance FeC03 | 2.10× 10 11 CdC03 | 1.80 × 10 14 CO3ValueUnits alne Submit Hints My Answers Give Up Review Part Part BExplanation / Answer
Iron carbonate dissolves and precipitaes according to the reaction equation :
FeCO3 (s) <=> Fe2+(aq) + CO32- (aq)
solubility product is given by :
Ksp1 = [Fe2+] * [CO32-]
The precipitation of FeCO( starts, when the product of iron(II) ion molarity and carbonate ion mloarity on right hand side reaches the value Ksp on kleft hand side. So for given a value of [Fe²] precipiation starts when carbonate ion reaches the level:
[CO32-] = Ksp1 / [Fe2+] = ( 2.10 * 10-11 ) / (1.24*10-2 ) = 1.69 * 10-9 M -----(1)
Cadmium carbonate dissolves and precipitaes according to the reaction equation :
CdCO3(s) <=> Cd2+(aq) + CO32-(aq)
solubility product is given by
Ksp2 = [Cd2+] * [CO32-]
Due to the smaller value of its Ksp Cadmium carbonate precipitates at lower level of [CO32-] .
When you increase the carbonate ion concentration CdCO3 precipiates such that [Cd2+] decreases and solubility product equation is still satisfied.
The cadmium ion concentration for certain level of carbonate is given by :
[CO32-] = Ksp2 / [Cd2+] = (1.80*10-14 ) / (1.58*10-2 ) = 1.14*10-12 M -----(2)
as the concentration of [CO32-] in case of CdCO3 smaller than that of FeCO3 , so CdCO3 precipitates first.
therefore [CO32-] = 1.14*10-12 M -------(it the answer )