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Topic: Zinc Sulfate Precipitate ?  (Read 7886 times)

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Offline Papyroro

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Zinc Sulfate Precipitate ?
« on: December 05, 2013, 02:29:31 AM »
Hi guys,

I'm a biologist and lately obtain a precipitate (white) when mixing my solution. I'm curious to know what it is. Does someone have an idea.

I'm mixing Zinc Sulfate (ZnSO4 ; 7 H2O) with PBS which contains :
Potassium Chloride (KCl)          200.0 mg/L    2.6666667 mM
Potassium Phosphate monobasic (KH2PO4)       200.0       1.4705882
Sodium Chloride (NaCl)             8000.0       137.93103
Sodium Phosphate dibasic (Na2HPO4-7H2O)    2160.0       8.059702

Thanks for your help !

Offline Borek

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Re: Zinc Sulfate Precipitate ?
« Reply #1 on: December 05, 2013, 02:32:50 AM »
There is an obvious suspect.

Have you heard about solubility rules?
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Offline Papyroro

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Re: Zinc Sulfate Precipitate ?
« Reply #2 on: December 05, 2013, 02:41:27 AM »
So from what I read Sulfate are usually soluble... Sulfide aren't... Do you think my precipitate is sulfide ?

I'm actually interested in the zinc in my experiments, that would mean that my zinc is not part of the precipitate ?

Offline kriggy

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Re: Zinc Sulfate Precipitate ?
« Reply #3 on: December 05, 2013, 02:52:08 AM »
So from what I read Sulfate are usually soluble... Sulfide aren't... Do you think my precipitate is sulfide ?

I'm actually interested in the zinc in my experiments, that would mean that my zinc is not part of the precipitate ?

I dont think it is sulfide, there are no S2- ions in your solution

Offline Papyroro

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Re: Zinc Sulfate Precipitate ?
« Reply #4 on: December 05, 2013, 02:58:25 AM »
Here's what I got for the solubility :

1. Salts containing Group I elements are soluble (Li+, Na+, K+, Cs+, Rb+). Exceptions to this rule are rare. Salts containing the ammonium ion (NH4+) are also soluble.
2. Salts containing nitrate ion (NO3-) are generally soluble.
3. Salts containing Cl -, Br -, I - are generally soluble. Important exceptions to this rule are halide salts of Ag+, Pb2+, and (Hg2)2+. Thus, AgCl, PbBr2, and Hg2Cl2 are all insoluble.
4. Most silver salts are insoluble. AgNO3 and Ag(C2H3O2) are common soluble salts of silver; virtually anything else is insoluble.
5. Most sulfate salts are soluble. Important exceptions to this rule include BaSO4, PbSO4, Ag2SO4 and SrSO4 .
6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble. Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition metals and Al3+ are insoluble. Thus, Fe(OH)3, Al(OH)3, Co(OH)2 are not soluble.
7. Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag2S are all insoluble. Arsenic, antimony, bismuth, and lead sulfides are also insoluble.
8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other insoluble carbonates include FeCO3 and PbCO3.
9. Chromates are frequently insoluble. Examples: PbCrO4, BaCrO4
10. Phosphates are frequently insoluble. Examples: Ca3(PO4)2, Ag3PO4
11. Fluorides are frequently insoluble. Examples: BaF2, MgF2 PbF2.

Something happening between the phosphate groups and the sulfates ?. Damn I should have paid more attention to the organic chemistry at Uni :)

Offline kriggy

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Re: Zinc Sulfate Precipitate ?
« Reply #5 on: December 05, 2013, 03:21:51 AM »
I think so.
The salts you have in solution are dissociated so it consists of Zn2+, K+, Na+, Cl- H2PO4- and HPO42- ions and they can interact with each other

Offline Borek

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Re: Zinc Sulfate Precipitate ?
« Reply #6 on: December 05, 2013, 04:20:49 AM »
Something happening between the phosphate groups and the sulfates ?

This is either wrong, or right, depending on what you thought when you wrote what you wrote.

Solubility rules refer to combinations of cation (metal) and anion (from the acid).
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Offline opsomath

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Re: Zinc Sulfate Precipitate ?
« Reply #7 on: December 06, 2013, 11:39:23 AM »
My bet is on zinc phosphate, which is a common insoluble coating.

http://en.wikipedia.org/wiki/Zinc_phosphate

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