Sciencemadness Discussion Board

help crystal seperation. need explanation.

Sonar - 17-2-2015 at 11:36

I am new to amateur chemistry I don't yet understand all the formulas so be nice to me lol.
Anyway I made up a solution of copper sulfate I then added sodium bicarb to make copper carbonate i then filtered the solution, long story short I added aluminum and got a reaction, the copper and aluminum swapped places leaving with a solution of alum and sodium. I'm sure this all sounds normal to most of you but what I need explained is this: I use Zep shower tub and tile cleaner to descale my glassware it contains sulfamic acid, glycolic acid and alcohol. I sprayed some in a beaker and let it sit, came back a while later and it had crystalized, however I had forgotten that I sprayed it in there, I thought is was from my alum and sodium solution(I know, dumb. right!) So I scraped so crystals out and dropped them in my solution of sodium and alum. I realized my error almost immediately, but all was not lost because crystal began forming in the solution. What i have figured out is that the Zep caused the sodium to separate from the solution. Can anyone tell me why??

Texium - 17-2-2015 at 13:29

Well, it sounds like you've got a whole slurry of stuff there. I really don't have any idea what's going on with it. With so much stuff mixed like that, you can't really tell.
I recommend scrapping it and starting over. It's unlikely you'd be able to retrieve anything useful from what you have now.

Sonar - 18-2-2015 at 08:01

It was all very useful I retrieved alum and sodium, I just trying to figure out why the sodium crystalized out of the solution when I accidentally dropped some crystals in from the Zep.

Amos - 18-2-2015 at 08:07

What do you mean "The sodium crystallized out of solution"? It can't just be "sodium" it has to be sodium carbonate, sodium sulfate, sodium sulfamate; something. And how are you so sure that it is not an aluminium compound that crystallized out?

In any case, your crystals are likely not a single compound but several, owing to how messy your starting solution was.

blogfast25 - 18-2-2015 at 08:17

Sonar:
Quote: Originally posted by zts16  
Well, it sounds like you've got a whole slurry of stuff there. I really don't have any idea what's going on with it. With so much stuff mixed like that, you can't really tell.
I recommend scrapping it and starting over. It's unlikely you'd be able to retrieve anything useful from what you have now.


Listen to that. It's correct. From that kind of 'mess' it's hard to deduce anything.

Copper carbonate by the way is Cu2CO3(OH)2, a basic copper carbonate.

Why prepare that and then add Al to it? Why not just add the Al to your copper sulphate solution?

[Edited on 18-2-2015 by blogfast25]

gdflp - 18-2-2015 at 08:38

Quote: Originally posted by blogfast25  
Why not just add the Al to your copper sulphate solution?



I don't believe that those two will react without some chloride contamination due to the Al2O3 passivation layer.

blogfast25 - 18-2-2015 at 09:05

Quote: Originally posted by gdflp  

I don't believe that those two will react without some chloride contamination due to the Al2O3 passivation layer.



Oh, but I can assure you that it does: with GREAT gusto even. Get it wrong and you end up with an over-boiling test tube: it's quite exothermic.

You're over-estimating the passivation effect. The passivation layer protects against oxygen but oxygen is quite a sluggish oxidiser.

[Edited on 18-2-2015 by blogfast25]

gdflp - 18-2-2015 at 09:17

Interesting, I just tried it. Dissolved some copper sulfate in distilled water in a test tube, heated it to 40°C ish and dropped in a piece of aluminum foil. After 5 min, no reaction visibly occurred at all, the Al is still shiny. I'll let it sit for a while, but I don't think much will happen very quickly.

blogfast25 - 18-2-2015 at 09:28

Quote: Originally posted by gdflp  
Interesting, I just tried it. Dissolved some copper sulfate in distilled water in a test tube, heated it to 40°C ish and dropped in a piece of aluminum foil. After 5 min, no reaction visibly occurred at all, the Al is still shiny. I'll let it sit for a while, but I don't think much will happen very quickly.


Well, that's strange. I've done this many times. Even my daughter's chemkit had such an experiment in it and worked too, many years ago. :o

Also, in the OP's experiment there was no chloride and copper basic carbonate would be slower because it's so insoluble.

Please give it a bit more time.

[Edited on 18-2-2015 by blogfast25]

Molecular Manipulations - 18-2-2015 at 09:40

I think it does need some halide ion to get going. Most copper sulfate has at least a little chloride contamination in it. This paper says that aluminum doesn't even react with pure sulfuric acid http://khimiya.org/pdfs/KHIMIYA_19_3_PETRUSEVSKI.pdf
Quote:

Thus, according to Glinka [4]
and Brady [5], aluminium reacts with diluted acids displacing hydrogen, while Greenwood
& Earnshaw [6] say that the protective oxide cover prevents any reaction with
diluted acids. On the other hand, the experiments show [7] that the only reaction that
occurs in real time with diluted acids at room temperature is the reaction with HCl(aq),
giving rise to hydrogen gas and aqueous solution of aluminium chloride. Therefore, the simple chemical reaction perative for strong acids other than HCl!

Every time I've reacted tech. grade copper sulfate with aluminum it takes a long time, but eventually starts, at that point the reaction gets very fast.
Then once I recrystallized it thrice and no reaction occurred over a 24 hour period!

blogfast25 - 18-2-2015 at 09:49

I've dissolved aluminium in dilute acids literally countless times, including H2SO4, even for commercial purposes.

Molecular Manipulations - 18-2-2015 at 09:52

Right, of course. All that means is that your acid is impure, according to the paper I linked. Don't argue with me, I didn't do the experimenting. I doubt your acid was completely free of chloride contaminates.

blogfast25 - 18-2-2015 at 10:08

Quote: Originally posted by Molecular Manipulations  
Right, of course. All that means is that your acid is impure, according to the paper I linked. Don't argue with me, I didn't do the experimenting. I doubt your acid was completely free of chloride contaminates.


Don't argue with you??? Excuse me?

What makes your experiments better than mine? How do you know the acids are contaminated?

And your paper is G-d????

Dear me. This is a forum about science, don't you know?

Nitric acid is an oxidising acid BTW. It passivates several metals.

[Edited on 18-2-2015 by blogfast25]

gdflp - 18-2-2015 at 10:22

Quote: Originally posted by blogfast25  
Quote: Originally posted by gdflp  
Interesting, I just tried it. Dissolved some copper sulfate in distilled water in a test tube, heated it to 40°C ish and dropped in a piece of aluminum foil. After 5 min, no reaction visibly occurred at all, the Al is still shiny. I'll let it sit for a while, but I don't think much will happen very quickly.


Well, that's strange. I've done this many times. Even my daughter's chemkit had such an experiment in it and worked too, many years ago. :o

Also, in the OP's experiment there was no chloride and copper basic carbonate would be slower because it's so insoluble.

Please give it a bit more time.



Yep, I'm going to let it sit for a while to see if I get a reaction. I completely agree that basic copper carbonate would take much longer, but I don't think it would work well with pure cupric sulfate. I'm using tech grade cupric sulfate, so we'll see what happens. Did you use tap water in your experiments, if so the chloride contamination may have come from there?

blogfast25 - 18-2-2015 at 10:29

Quote: Originally posted by gdflp  
Did you use tap water in your experiments, if so the chloride contamination may have come from there?


No, always DIW.

Chloride has an effect, no contest. But I think you're over estimating the effect that trace amounts of chloride would have.

High concentrations, large effects. Small concentrations, small effects. Broadly speaking.

[Edited on 18-2-2015 by blogfast25]

MrHomeScientist - 18-2-2015 at 11:11

My experience has also been that no reaction is observed between Al and CuSO<sub>4</sub> solution, with added chloride allowing it to happen fairly quickly. I could see it reacting if it's freshly cut Al, since it hasn't had time to passivate. I can also attempt this and see what happens when I get home tonight.

blogfast25 - 18-2-2015 at 11:13

Another thing that should work is a small drop of acid.

Molecular Manipulations - 18-2-2015 at 11:18

Fine, argue all you want. All I said was I didn't do the research, so what I say makes no difference.
I meant "don't argue with me, cause I'm no authority on this subject."
Quote:
What makes your experiments better than mine? How do you know the acids are contaminated?

My experiments? What experiments?
I posted a paper which claimed that halide free acids don't act upon aluminum. Is that true? I've no idea, but unless you can prove that your acid had no halide ions and still reacted with aluminum, I don't see your point.
My experiment had only to do with copper sulfate, and all I noticed was that before recrystallization, it reacted readily with aluminum, afterward it did not. That has not a thing to do with your acid or the author of that paper's.

gdflp - 18-2-2015 at 14:47

Okay, I just checked and the copper sulfate did react with aluminum, but it was very slow and the solution is still noticeably blue with only a small amount of copper precipitate.

blogfast25 - 18-2-2015 at 16:37

Quote: Originally posted by Molecular Manipulations  
I posted a paper which claimed that halide don't act upon aluminum. Is that true?


You presented a paper about NITRIC ACID and chlorides, not about 'free acids' in general.

HNO3 is an oxidising acid and it passivates many metals, I'm not sure about Al.

With chlorides HNO3 forms nitrosyl chloride, see Aqua Regia. Nitrosyl chloride is a very powerful oxidiser.

I don't know if my (very decent) H2SO4 contains any chlorides but it's very presumptuous of you to assume it does, either way.

People dissolve Al in acids all the time. It's non-problematic.