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Offline sinjid9

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Solubility Question
« on: August 26, 2011, 02:24:17 AM »
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.

Offline Dan

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Re: Solubility Question
« Reply #1 on: August 26, 2011, 03:12:48 AM »
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.
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Offline sinjid9

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Re: Solubility Question
« Reply #2 on: August 26, 2011, 10:31:08 PM »
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.
« Last Edit: August 26, 2011, 10:58:13 PM by sinjid9 »

Offline Borek

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Re: Solubility Question
« Reply #3 on: August 27, 2011, 04:08:34 AM »
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.
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Offline Fluoroantimonicacid

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Re: Solubility Question
« Reply #4 on: August 27, 2011, 04:31:01 AM »
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  :rarrow: CH3COOAg + NO3-
Also, NiS isn't soluble too.

Offline sinjid9

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Re: Solubility Question
« Reply #5 on: August 27, 2011, 01:35:33 PM »
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?

Offline Fluoroantimonicacid

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Re: Solubility Question
« Reply #6 on: August 27, 2011, 04:49:31 PM »
Hey,I got it. Your teacher said "determine" the presence of ions. If there are S2- 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.

Offline Raphael

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Re: Solubility Question
« Reply #7 on: August 27, 2011, 05:02:45 PM »
Hey,I got it. Your teacher said "determine" the presence of ions. If there are S2- 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 S2- coming from? I see no sulfur.

Offline Fluoroantimonicacid

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Re: Solubility Question
« Reply #8 on: August 27, 2011, 05:07:26 PM »
There is S2- in starting solution, so if there is nickel acetate in starting solution, NiS will precipitate.

Offline sinjid9

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Re: Solubility Question
« Reply #9 on: August 27, 2011, 08:05:38 PM »
Hey,I got it. Your teacher said "determine" the presence of ions. If there are S2- 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?

Offline Borek

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Re: Solubility Question
« Reply #10 on: August 28, 2011, 03:55:38 AM »
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.
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Offline sinjid9

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Re: Solubility Question
« Reply #11 on: August 28, 2011, 04:34:14 PM »
Well I don't know actually, it's grade 11 Chem. How do you know which compound is better suited for this reaction?

Offline Borek

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Re: Solubility Question
« Reply #12 on: August 28, 2011, 05:28:33 PM »
The simpler, the better. Sodium acetate is simple.
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Offline sinjid9

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Re: Solubility Question
« Reply #13 on: August 28, 2011, 09:44:26 PM »
What do you mean by simple? You mean not a transition metal?

Offline Borek

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Re: Solubility Question
« Reply #14 on: August 29, 2011, 03:32:04 AM »
Yes, when you want to add an anion, usually just acid or salt of some alkali metal is the best approach.
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