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Mixell
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Nah, mixing with K2SO4 or H2SO4 will do nothing if its Fe III sulfate.
Just check the pH of the solution!
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barley81
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Add NaOH and you should get rusty brown precipitate indicating iron III.
Since you have identified iron III, it can only be the sulfate because that's the only iron III salt possible (your list).
Mixell - yeah, it's ferric sulfate. Sorry 'bout that. If you look up pictures on google images, many samples are yellow as well...
[Edited on 4-6-2012 by barley81]
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Amm
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No we don't have to work under the fume hood, we did mix it with NaOH, and it made a rusty solution
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Mixell
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So I think we made a conclusion =)
Next compound?
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Hexavalent
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Do you mean a rusty-coloured solution/precipitate?
I second what barley said....iron (II) and iron (III) compounds tend to have brownish hydroxides that are insoluble IIRC.
Next compound?
[Edited on 4-6-2012 by Hexavalent]
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Amm
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Ok we have 3 other unknown subsatances, any knowledge you can share is greatly appreciated.
Unknown letter A- nothing note worthy happened when mixed with NaOH, K2SO4 or AgSO4
Appeared to dissolve in each
Unknown letter B
-Mixed with AgSO4
It formed white soft blobs that stuck to the side of the glass
Unknown letter c
-mixed with NaoH
Turned a white, milky color
-Mixed with K2SO4
 
made a cloudy solution appeared to be a precipitate
-Mixed with AgSO4
 
Turned brown or purple
Unknown letter D (suspected Iron III Sulfate)
- Turned each solution a rusty orange color
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a.dunn.wa
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Well we do have access to just simple lab stations (just tables) as well. But I'm intrigued to see where you are going because, if it is something
that would be really helpful I think we could convince our teacher to let us perform it.
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a.dunn.wa
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Quote: Originally posted by Mixell  | Nah, mixing with K2SO4 or H2SO4 will do nothing if its Fe III sulfate.
Just check the pH of the solution! |
How would one go about checking the pH. Just want to make sure we are on the same boat here, because this is what we're planning on doing:
Adding water to the unknown compound; then using a pH strip to test it. Is that all there is to it?
Also how do you guys know this is Fe III and not Fe II sulfate? Would the pH reveal that? What is the pH of these two compounds supposed to be?
Sorry about all the questions, we really appreciate your guys time!!!
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Mixell
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Fe II solution should be neutral, Fe III should be acidic:
Fe3+ +H2O --> Fe(OH)2+ + H+
Use the blue litmus paper, if its acidic, it will turn red.
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Mixell
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Remember: always add the chemicals gradually with mixing.
I'll start from C:
Strontium and calcium hydroxide (especially the calcium hydroxide) are not very soluble.
Also the sulfates are pretty insoluble.
But the brown/purple suspension makes me think that its a suspension of silver, thus there is a reducing agent in the solution.
Tin II (and Fe II) is a reducing agent, but should not form a precipitate with sulfate.
And the only somewhat reducing sugar on your list is starch, but it is not soluble in water.
Please check the conductivity of the solution.
And if you can, add some nitric acid to your solution and heat it up (do it in the fume hood) and report if a brown gas appears (NO2) or add sulfuric
acid and hydrogen peroxide. Then check the solution with silver nitrate (or sulfate if there is no nitrate and report if there is a precipitate (it
should be a very noticeable precipitate).
B:
I assume it only reacts with the silver sulfate?
Then it is a solution of chloride/bromide/iodide.
Add some nitric acid to it, or hydrogen peroxide and sulfuric acid. If the color of the solution turns purple and there is a black/purple precipitate,
then its iodine. If it turns yellow (noticeably) it is bromine. And finally, add sulfuric acid +hydrogen peroxide/ KMnO4 and put a moist KI/NaI
(iodine paper) on top of the test tube, may be even try to seal it with your thumb for a faster result. If the iodine paper turns purple, then its
chlorine.
And to detect if its sodium or potassium, use a flame test.
A:
Check the conductivity of the solution and report.
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Amm
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Unknown letter c
- We burned this unknown, it appeared to produce a liquid
-burned a white color
 
During burning
 
After burning
-We also Mixed it with our Unknown letter D, identified as iron III sulfate
- Appeared that a precipitate formed
 
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a.dunn.wa
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UPDATE #2:
Alright, so here is where we are at guys. We have two days left in the lab (on Thurs and Fri) and that's it to identify these three unknowns.
My lab partner has the pics for what they are worth, and will be posting them later.
Unknown D (suspected Fe): Tested pH of it today w/ blue litmus paper. Turned the paper red. As stated by Mixell Fe III should be acidic so we
are going to conlclude that unknown D is Fe III sulfate.
Unknown C: Still not sure what it is, but we have a lot of results for it.
---C + water --> cloudy white precipitate
---Using phenol red, we found C to be basic
---Using distilled water, we found the elec. conductivity of C to be medium...the equipment we used just had a green and red light
and a general key on the back.
---C + a sulfate (either H2 or K2, drawing a blank right now) --> a precipitate
---When C was burned it bubbled and turned brown over time...is this hydrolysis? (we do have a pic of this)...I know tin II chloride would
hydrolysize...what do you guys make of this??
---burned white color
---In 0.1 M NaOH, C created a white, milky precipitate
Unknown B:
---Using phenol red, B was determined to be basic
---Elec conductivity in distilled water was high
---burned bright, vivid, persistent, orange
Unknown A:
---highelec. conductivity in distilled water
---burned deep, strong orange color
So what do you guys make of all this? We really appreciate any help/assistance you guys can give us...also are there any more tests you would have us
try? The chemicals we have available are as follows (same as in OP):
Water
Ethanol
Red and blue litmus paper
0.1 M silver nitrate solution*
Bromothymol blue indicator
Phenolphtalein indicator
0.1 M NaOH solution
0.1 M K2SO4 solution*
phenol red indicator
0.1 M HCl
0.1 M H2SO4
Thanks guys!
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Hexavalent
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a.dunn.wa - AJKOER said 'If no reaction with HCl, do NOT react with H2SO4 as you may have NaF and heating with H2SO4 can produce deadly HF fumes.'
I'm surprised that they gave you NaF in the list of possibilities, particularly if you don't work in the fumehood. Although the amounts would be very
small, HF gas works wonders to the human body in the most horrific of ways.
Most of the other tests are fairly nonhazardous, however, and I don't think they *would* give you NaF if you also had H2SO4.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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a.dunn.wa
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Also worth noting is that Unknown Substance B is hygroscopic. Which limits it down to these according to Wikipedia:
1. Aluminum nitrate
2. Ammonium chloride
3. Calcium chloride
4. Calcium nitrate
5. Magnesium carbonate
6. Magnesium sulfate
7. Potassium carbonate
8. Sodium bisulfate
9. Sodium carbonate
10.Sodium iodide
11. Sodium nitrite
12. Sodium sulfate
The fact that it burns orange makes me believe it has calcium in it. What do you guys think?
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Hexavalent
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No, calcium's flame test is brick red. Orange points to a sodium compound, usually, but the orange could be masking another, maybe weaker colour, such
as the white exhibited by magnesium compounds, the very pale green[1] seen by ammonium species etc. Do you have access to a cobalt glass square or
something to see the proper colours of the flame?
From there, you can check pH for sodium bisulfate, reaction with an acid for the carbonate, AgNO3 precipitation test for the iodide, heating it up and
see if it decomposes if its the nitrite (and what products are formed). The sulfate could then either be determined by the process of elimination, OR
by taking a melting point (884 °C (anhydrous)
32.38 °C (decahydrate)) or begging your teacher for some barium chloride solution
You could also possibly look up some melting points for the otherchemicals, and determine which compound you have that way....although you may have
trouble as many ionic compounds have really high melting points.
[1] From 'The Illustrated Guide to Home Chemistry Experiments', Laboratory 19.1 - Use Flame Tests to Discriminate Metal Ions
[Edited on 5-6-2012 by Hexavalent]
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Mixell
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C:
A good chance it is Tin II chloride, please check with the procedure I described.
B:
Might be sodium carbonate or sodium acetate/borate/oxalate/citrate. Add H2SO4, if bubbles appear, it's the carbonate. If it smells like vinegar, it's
the acetate. Report.
A:
Might be sodium fluoride/nitrate/sulfate/ etc.. check the pH please.
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Amm
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Could we identify C using a burn test? we don't have access to a lot of chemicals.
Also Unknown A is basic.
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Mixell
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A:
If A is basic, then it's probably the salt of sodium and a weak acid, but a one that does not form a precipitate with silver ions.
It might be citrate/borate.
B:
Do the acid test, and report if bubbles are formed (and/or any other effects or smells, like the smell of vinegar).
C:
Test with silver nitrate and report (very likely it is Tin II chloride).
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Amm
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We mixed b with h2so4 and it smelled like vinager we are thinking sodium acetate
We mixed c with silver nitrate and it formed a precipitate we are thinking tin ii chloride
[Edited on 7-6-2012 by Amm]
[Edited on 7-6-2012 by Amm]
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Hexavalent
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Those are possible, just please, when writing formula, be more careful with your lettering, e.g. sulfuric acid is H2SO4, not
h2so4. At the least, use H2SO4, but the use of subscript as seen here is favourable.
We understand what you mean, but later in your chemistry career when things get more difficult, it will be absolutely necessary - e.g. Co is cobalt,
but CO is carbon monoxide . . .two very different things.
[Edited on 7-6-2012 by Hexavalent]
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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a.dunn.wa
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UPDATE:
Final update. Tomorrow we have 50 mins, and then our identifications of the compounds are due. We still need help identifying three, but we feel
confident that we have enough data and info to nail these. Please help any way you guys can.
1. Our teacher gave us help by letting us check our answers once with the correct answers, and gave us some helpful hints while doing so.
For Unknown A: we guessed sodium sulfate. He said that it does have Sodium, but is not sulfate. Our new hypothesis is that is is sodium acetate,
because it has a distinct, vinegar-like odor, when mixed with HCl. Other pieces of supporting evidence are that the compound is ACIDIC, burns
yellow/orange (sodium indication), and forms a white precipitate with AgNO3
For Unknown B: we gussed sodium acetate. He said that it does have sodium, but it is not acetate. We are not sure what B is. Other observations about
B is that it is very hygroscopic. When mixed with H2SO4 a strong, pungent, vinegar smell is made (this made us think
acetate...). Other tests showed that it dissolved, colorless in NaOH, burned a strong orange color (indication of sodium), was found to be basic, and
had a high elec. conductivity.
For Unknown C: we gussed potassium bromate. He said that it doesn't have either, but the second part is very close to bromate. He eventually told us
it was either Cl or I for the second part. The main point of evidence is that when burned it burned a white/purple color, which we
took as potassium but he said that another metal on our list burns purple/white. Does anyone know what that metal is??? Other facts
about this compound include that it made a white, milky precipitate when mixed with NaOH, made a purple-colored solution when mixed with
AgSO3, is basic, and makes water a cloudy white color when mixed. Anyone have an idea??
We really appreciate all your guys help. It has been beyond helpful for us. If you need to know anything else, please let us know, and we will try to
help you guys help us.
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a.dunn.wa
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Also, just for reference again, here are the list of all the possibilities:
Aluminum hydroxide
Aluminum nitrate
Ammonium chloride
Barium sulfate
Calcium chloride
Calcium sulfate
Iron II sulfate
Iron III sulfate
Lauric acid
Magnesium carbonate
Magnesium hydroxide
Magnesium sulfate
Potassium bromate
Potassium carbonate
Potassium chloride
Potassium iodide
Potassium metabisulfite
Potassium nitrate
Potassium persulfate
Potassium phosphate
Potassium sodium tartrate
Potassium thiocyanate
Sodium acetate
Sodium bisulfate
Sodium borate
Sodium bromide
Sodium carbonate
Sodium chloride
Sodium citrate
Sodium fluoride
Sodium iodide
Sodium nitrate
Sodium nitrite
Sodium oxalate
Sodium phosphate
Sodium sulfate
Sodium sulfite
Sodium thiosulfate
Starch
Stearic acid
Strontium chloride
Strontium hydroxide
Strontium nitrate
Sucrose
Tin II chloride
Urea
Zinc nitrate
Zinc sulfate
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Amm
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[Edited on 7-6-2012 by Amm]
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a.dunn.wa
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After thinking about this for another hour now, I think we can draw a couple more conclusions...
Unknown C is Tin II sulfate. Since the compound burns a purple/white color and is not potassium, a lot of possibilities are eliminated (all potassium,
sodium, strontium, aluminum, calcium, iron, barium compounds). Then once all of those are eliminated, I took into consideration the fact that it HAS
to have chlorine or iodine. That leaves tin II chloride as really the only logical choice left. And we also got something very very similar as shown
in this video someone else took (assuming they started with water):http://www.youtube.com/watch?v=epd-DAE_sE When they add in the tin ii sulfate that
is pretty much what our unknown did. Please let me know if you agree/disagree, or if there is any problems in my reasoning that aren't technically
sound.
Unknown A is sodium acetate. First, I started with the definites. Our teacher told us that this had sodium guaranteed, so everything without sodium
was eliminated. That narrows it down to 16 minus the one sodium we already guessed (sulfate). The fact that the compound is acidic (sodium acetate is
acidic as I found here http://answers.yahoo.com/question/index?qid=20110525035727AA...) and the fact that it had a distinct vinegar odor makes me believe it is sodium
acetate.
Unknown B I am still not sure of. Since it has sodium, and isn't sodium acetate, that narrows it down to 15 possibilities. The fact that it is basic
eliminates some possibilties but I'm still not sure...anyone have any ideas for this one? Maybe citrate?
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Hexavalent
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I believe sodium acetate is actually basic . . .the acetate ion acts as a Bronstead-Lowrey base in a reaction with water, or, in other terms, sodium
acetate dissociates in water into sodium and acetate ions. Sodium ions react very little with hydroxyl ions whereas acetate ions combine with hydrogen
ions to produce neutral acetic acid, and the net result is a relative excess of hydroxyl ions, causing a basic solution.
Here the basic properties of sodium acetate are taken advantage of; http://www.youtube.com/watch?v=kH19EIf5GtE
and here;
http://www.youtube.com/watch?feature=iv&annotation_id=an...
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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