Spualunstrov 3. A solution contains 0.050 M Ca*, 0.050 M Zn\' and 0.050 M Ni2+ i

Question

Spualunstrov 3. A solution contains 0.050 M Ca*, 0.050 M Zn' and 0.050 M Ni2+ ions. a. If you separate them using aqueous (NH) C O, which ion will precipitate first as an oxalate? Consider the K values for CaC,O, ZnC,O, and NiC,O, on page 86. b. Calculate the concentration of the oxalate ion when the first cation (Ca", Zn*, or Nil+) begins to precipitate. 2. c. Explain why NiC,O, and ZnC,O, do not actually precipitate with CaC,O, during rocedure 8 of Quialitative Analysis scheme. (Hint: See the formation constants on Formatiov 2s page 86.) Ca

Explanation / Answer

For NiC2O4, Ksp = [Ni2+][C2O42-] = 4 X 10-10

For ZnC2O4, Ksp = [Zn2+][C2O42-] = 1.5 X 10-9

For CaC2O4, Ksp = [Ca2+][C2O42-] = 1.3 X 10-9

At equilibrium small Ksp values mean that the substance is not very soluble and will precipitated. Hence, NiC2O4 and ZnC2O4 donot precipitate with CaC2O4. NiC2O4 will precipitate first , then caC2O4 and finally ZnC2O4.

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