Question

A solution contains .04 M Ca+, .04 M Zn2+, and .04 M Ni2+ ions.

A) If you separate them using (NH4)2C2O2, which ion will precipitate first as an oxalate? Consider Ksp Values for CaC2O4, ZnC2O4, and NiC2O4.

CaC2O4 Ksp = 1.3 x 10^-9

ZnC2O4 Ksp = 1.5 x 10^-9

NiC2O4 Ksp = 4.0 x 10^-10

B) Calculate the concentration of the oxalate ion when the first cation (Ca2+, Zn2+, or Ni2+ begins to precipitate.

C) Explain why ZnC2O4 and NiC2O4 do not actually precipitate with CaC2O4.(during procedure 8 of Qualitative Analysis)

Answer 1

@ Ksp (Niçow) < Ksp (21(204) < Ksp (cal.ou) Since Solubility product of Nicou is less than the first as an Oxalate. two others, it will pricipitate B [Ni2+] = 0.04 M (M= mol/L) | S «i , ex) = [Nºt] [c,ốt”] ov, 4.0X10-10 - (0.04) (x) or; x = 4x10-10 = 1x10-8 M 0,04 e this is the concentration when of Oxalate ion Ni 2+ begins to precipitate. @ Arte Sp According to the Ksp order above Nic204 and Znč, Oy Cannot precipitate coite Cacy Qu. as the latter One is high Solubility product. solubility That means Cae, ou is neo has greater than the other two compounds. So, when NiQQ4 18 precipitating followed by Zuc,ou, CaC, Qy will still remain soluble in solution. is the equilibrium Note: bos Ksp between the compound and its Corresponding ions in Solution. More ious means more ksp which means more Solubility,