ScienceHideout
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Hydrogen Sulfide... In Acidic Medium?
A qualitative test that I must do requires me to use H2S in an acidic medium... The problem is, I don't exactly know what this means. Do I dissolve
the H2S in acid, or do I bubble it through the unknown after it is acidified? How exactly does this work, and what does it mean? What is H2S in a
basic medium?
Thanks,
Dean 
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Texium
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Maybe it means aqueous hydrogen sulfide (hydrosulfuric acid)?
What is the test, and what are you testing?
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blogfast25
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It maybe related to the pH selective precipitation of some transition metal sulphides. In that method the solution of metals is acidified and hydrogen
sulphide is then gassed through it to saturation. Certain metals will precipitate as sulphides, some not.
The solubility of H2S is remarkably independent of pH, so it dissolves more or less equally well in acid, neutral or alkaline solutions.
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ScienceHideout
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It is a qualitative test to distinguish between Hg2+, Bi3+, Cu2+, Cd2+, As3+, As5+, Antimony ions, tin ions, versus iron, chromium, aluminum, cobalt,
nickel, manganese, zinc, alkali, and alkaline ions
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blogfast25
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Quote: Originally posted by ScienceHideout  | | It is a qualitative test to distinguish between Hg2+, Bi3+, Cu2+, Cd2+, As3+, As5+, Antimony ions, tin ions, versus iron, chromium, aluminum, cobalt,
nickel, manganese, zinc, alkali, and alkaline ions |
Going by memory, the former group will precipitate, the latter not.
This is due to the solubility products: the former group has much lower solubility products than the latter. As a result the required
S<sup>2-</sup> concentration needed for precipitation is achieved much more easily for the former group.
Since as H2S + 2 H2O < === > S2- + 2 H3O+, this means that [S2-] can be controlled by pH. This is true because [H2S] is more or less
independent of pH.
[Edited on 11-5-2014 by blogfast25]
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ScienceHideout
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by ScienceHideout | | It is a qualitative test to distinguish between Hg2+, Bi3+, Cu2+, Cd2+, As3+, As5+, Antimony ions, tin ions, versus iron, chromium, aluminum, cobalt,
nickel, manganese, zinc, alkali, and alkaline ions |
Going by memory, the former group will precipitate, the latter not.
This is due to the solubility products: the former group has much lower solubility products than the latter. As a result the required
S<sup>2-</sup> concentration needed for precipitation is achieved much more easily for the former group.
Since as H2S + 2 H2O < === > S2- + 2 H3O+, this means that [S2-] can be controlled by pH. This is true because [H2S] is more or less
independent of pH.
[Edited on 11-5-2014 by blogfast25] |
Correct. So do you think I can do this perhaps by adding acid to the solution, and then some ammonium sulfide, or do I need to add actual H2S?
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blogfast25
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You'll need to know how much acid to add to get to the pH needed. The method should tell you what pH is needed to achieve separation. You could also
use buffers to stabilise pH to a desired value. W/o accurate pH control this method will not work.
Adding ammonium sulphide should work. Add it slowly, bit by bit and preferably calculate the total amount you need.
Beware of H2S: very, very poisonous. Fume food as a MINIMUM safety measure!
[Edited on 11-5-2014 by blogfast25]
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