[sinjid9]

I had a quiz on solubility and one of the questions on it were, "You are given a solution that may contain acetate, sulphide and carbonate ions. Use a flowchart to explain how you would determine the presence of these ions.

I wrote
Magnesium Nitrate (aq) + Sodium Carbonate (aq) -> Magnesium Carbonate (s) + Sodium Nitrate (aq)
Filter Out the Magnesium Carbonate
(Got the mark)

Zinc Nitrate (aq) + Sodium Sulfide (aq) -> Sodium Nitrate (aq) + Zinc Sulfide (s)
Filter out the Zinc Sulfide
(Got the mark)

Silver Nitrate (aq) + Nickel Acetate (aq) -> Nickel Nitrate (aq) + Sodium Acetate (s)
Filter out the Silver Acetate
(Did not get the mark)

I'm curious how I didn't get the last mark. If someone could tell me what's wrong with it that would help.
My teacher circled the Nickel in both reactants and products of the last reaction.

[Dan]

Silver Nitrate (aq) + Nickel Acetate (aq) -> Nickel Nitrate (aq) + Sodium Acetate (s)
Filter out the Silver Acetate
(Did not get the mark)

I'm curious how I didn't get the last mark. If someone could tell me what's wrong with it that would help.

Should be silver acetate on the right hand side, not sodium acetate.

[sinjid9]

O wait, no I did write Silver Acetate but I typed it wrong on here, when I copied it over, sorry about that. So I guess thats not whats wrong with it.

[Borek]

Why nickel acetate, and not just sodium acetate?

Not that I can think of anything wrong about using nickel acetate, it is just rather unusual reagent.

[Fluoroantimonicacid]

Nickel acetate is very soluble in water,too. I think your teacher wants you to use sodium acetate instead of nickel acetate, or write the ionic equation like
 CH₃COO^- + AgNO₃  CH₃COOAg + NO₃^-
Also, NiS isn't soluble too.

[sinjid9]

Nickel acetate is very soluble in water,too.

That might be it, but how do you know it's very soluble in water? I know it's soluble.When I learned it we only used the general rules from the solubility table (similar to the one below)

Also is there anyone who's occupation revolves around Chemistry, that can help me with this question?

[Fluoroantimonicacid]

Hey,I got it. Your teacher said "determine" the presence of ions. If there are S^2- ions in solution, Ni(CH₃COO)₂ won't stay in the solution, NiS will precipitate out. So the reagent can't be Ni(CH₃COO)₂.

[Raphael]

Hey,I got it. Your teacher said "determine" the presence of ions. If there are S^2- ions in solution, Ni(CH₃COO)₂ won't stay in the solution, NiS will precipitate out. So the reagent can't be Ni(CH₃COO)₂.

Where is the S^2- coming from? I see no sulfur.

[Fluoroantimonicacid]

There is S^2- in starting solution, so if there is nickel acetate in starting solution, NiS will precipitate.

[sinjid9]

Hey,I got it. Your teacher said "determine" the presence of ions. If there are S^2- ions in solution, Ni(CH₃COO)₂ won't stay in the solution, NiS will precipitate out. So the reagent can't be Ni(CH₃COO)₂.

Well I wrote that I filter out the precipitate each time one forms. The idea is that we perform the procedure in that order and filter it out each time a precipitate forms. But would there still be Sulphide ions if I filter out the Zinc Sulphide precipitate at the end of the 2nd reaction?

[Borek]

Well I wrote that I filter out the precipitate each time one forms. The idea is that we perform the procedure in that order and filter it out each time a precipitate forms. But would there still be Sulphide ions if I filter out the Zinc Sulphide precipitate at the end of the 2nd reaction?

This can be easily calculated from Ksp. ZnS - 3x10^-23, NiS - 4x10^-20 (note: you will see different values in different sources, but they will be usually separated by three orders of magnitude). That means concentration of sulfides after ZnS precipitation should be too low for NiS precipitation.

But if the idea is to just test for ions, you don't want to filtrate the solution, it would be a waste of time. Then Ni is not selective enough.

[sinjid9]

Well I don't know actually, it's grade 11 Chem. How do you know which compound is better suited for this reaction?

[Borek]

The simpler, the better. Sodium acetate is simple.

[sinjid9]

What do you mean by simple? You mean not a transition metal?

[Borek]

Yes, when you want to add an anion, usually just acid or salt of some alkali metal is the best approach.