why
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distinguishing b/w solns
1. In order to distinguish between the following, a single reagent must be suggested:
a) AgNO3 & Zn(NO3)2 solns
b) HCl & HNO3
c) H2SO4 & HNO3
d) Pb(NO3)2 & Hg(NO3)2 solns
Can anyone give me some feedback:
a) add HCl : AgCl would ppt, while ZnCl2 is soluble in soln
b) add AgNO3 : AgCl would ppt, AgNO3 soluble
c) not sure
d) add K2CrO4 : PbCrO4 would ppt, but what happens to the mercury nitrate?
2. If [Ni 2+] = 0.2 M in soln, what concentration of H+ would prevent ppt'n of NiS by H2S?
Ksp for NiS = 3 x 10^ -21
K1K2 for H2S = 1.5 x 10^-21
[H2S] sat. = 0.12 M
I'm not even sure how to start this one
If someone could show me the right direction, it would be much appreciated
[Edited on 25-9-2004 by why]
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The_Davster
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a and b look good
c) Add solid copper, if a red poisonous gas is given off and/or the solution turns blue, the solution is HNO3
d) seems a bit more dificult, my solubility table is lacking(nonexistant) in terms of Hg2+, however sodium sulfate may work, lead sulfate should ppt
out.
Ah, just did a google Hg(II) sulfate decomposes in water to mercury (I) sulfate which is yellow and will ppt, where as lead (II) sulfate is white. So
essentially for d) add sodium sulfate, if ppt is yellow it is Hg2+, if ppt is white it is Pb2+.
Hope this helped
[Edited on 25-9-2004 by rogue chemist]
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neutrino
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For c, the solution turning blue wouldn't be a sure sign of HNO<sub>3</sub>. Remember that CuSO<sub>4</sub> is also blue
in solution, as are many copper salts.
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The_Davster
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Yes, but Cu does not react with sulfuric acid at normal temperatures.
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Mumbles
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I can think of a few more options that are less poisonous/easier to diferenciate.
A and B are good, and will work no problem.
C. I'd simply add Calcium Hydroxide. There will be a precipitate in the H2SO4 and no precipitate in the HNO3. No need to deal with hazardous
fumes
D. I'd personally go with the replacement method with this one. Just happens that copper will replace mercury, and not lead. You could either
look for the mercury metal, or look for the color change. The Mercury solution will begin to turn blue.
As for the second question I don't know. I'd have to look it up, that whole section never stuck with me 100%.
I'll do a little reasoning out, and hopefully it is right. the Ksp of Nickel Sulfide is 3 x 10^-21. That is the solubility in water basically.
So there can be 3 x 10^-21 M of the sulfide ion in the solution before it precipitates. Therefore the H+ conc. would be 6 x 10^-21 M because it is
twice as high as the Sulfide ion concentration. That would be my best guess, probably not right though.
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why
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Thanks for all the suggestions, everyone
Any takers on #2?
All I can think of is to find [S 2-] using Ksp=[Ni 2+][S 2-], since you know the Ksp and the nickel ion concentration. After that, I'm stuck...
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unionised
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I think the traditional answer to c would be barium chloride.
A pretty solution to d would be to add KI. Mercuric iodide is red and lead iodide is yellow. Both of these will dissolve in excess KI.
As for 2 you are half way there.
You can calculate a sulphide concentration at which NiS ppts.
then you need to work out from the concentration of H2S and the eqm constant for
H2S <----> 2H+ + S--
how much H+ you need to get that sulphide concentration.
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