Sciencemadness Discussion Board - Basic doubts on salts dissolving in water

Basic doubts on salts dissolving in water

edwin - 6-2-2015 at 18:03

I have some basic doubts.
When we dissolve some salts in water, are they separating as ions and do they exist as independent ions?
In the case of CuCl2 dissolved in water is it forming Cu(2+) and 2Cl(1-)?
If so, will that Cl(1-) react with hydrogen in water to form HCl?
Because, before adding CuCl2 water is showing pH~7 and after adding 0.1M of CuCl2 it turned to pH~4.5
Can we use this change in pH as a comparative measure to calculate number of Cu(2+) ions in the solution?
My aim is thin film preparation of CuS and need to get maximum Cu(2+) ions in the solution.

[Edited on 7-2-2015 by edwin]

[Edited on 7-2-2015 by edwin]

blogfast25 - 6-2-2015 at 18:55

Quote: Originally posted by edwin

I have some basic doubts.
When we dissolve some salts in water, are they separating as ions?
In the case of CuCl2 dissolved in water is it forming Cu(2+) and 2Cl(1-)?
If so, will that Cl(1-) react with hydrogen in water to form HCl?
Because, before adding CuCl2 water is showing pH~7 and after adding 0.1M of CuCl2 it turned to pH~4.5
Can we use this change in pH as a comparative measure to calculate number of Cu(2+) ions in the solution?
My aim is thin film preparation of CuS and need to get maximum Cu(2+) ions in the solution.

[Edited on 7-2-2015 by edwin]

That salts (ionic compounds) dissociate into their relevant ions on dissolution in water is about as well-evidenced as the sphericalness of the Earth. Put any doubts you may have on that firmly to bed, please.

No, the Cl- anions are perfectly stable in watery solution.

Pure CuCl2 on dissolution in water does indeed lower the pH of the solution somewhat due to very mild hydrolysis of the copper hexaqua cation:

[Cu(H2O)6]2+ + H2O === > [Cu(H2O)5(OH)]+ + H3O+

(Other types of complexed Cu ions, including smallish amounts of chloro complexes, are also found in a CuCl2 solution).

CuS is so extremely insoluble that even very dilute solutions of copper salts will precipitate CuS as long as minute amounts of sulphide ions (S2-

are present.

How do you plan to deposit these thin films and on what substrate?

[Edited on 7-2-2015 by blogfast25]

edwin - 6-2-2015 at 20:12

I am using SILAR method. Successive Ionic Layer Adsorption And Reaction(SILAR).
In this method, there will be one Cationic precursor solution and one anionic precursor solution.
In my case, I am taking CuCl2 dissolved in water as Cationic precursor.
The substrate used is glass slide.
While dipping the glass slides in the Cationic precursor, the Cu(2+) will get adsorbed over the substrate.
The excess or unbound Cu(2+) are removed by rinsing in double distilled water.
After that, it is dipped in Anionic solution containing Na2S dissolved in water.
The S(2-) ions will react with Cu(2+) in the substrate and get bounded to it. It is again rinsed in water.
This is one cycle, and it will be repeated to get a uniform film.

I am having a physics background. I am asking all this doubts as from my observations in the trial and errors conducted so far.

(i) In the cationic solution, is there any freely existing Cu(2+) ions, and is it them that gets bounded?
(ii) How the concentration, temperature,pH,etc... affects this binding process?
(iii) The Na2S solution, when prepared, is slightly yellowish. After some cycles it gets fully transparent. Is it because all the S(2-) are bonded with the Cu(2+) in the substrate, and there is no free S(2-) in the solution?.( I think this free sulfur gives yellow color)

Basic doubts on salts dissolving in water

edwin - 6-2-2015 at 21:10

I have some basic doubts.
When we dissolve some salts in water, are they separating as ions?
In the case of CuCl2 dissolved in water is it forming Cu(2+) and 2Cl(1-)?
If so, will that Cl(1-) react with hydrogen in water to form HCl?
Because, before adding CuCl2 water is showing pH~7 and after adding 0.1M of CuCl2 it turned to pH~4.5
Can we use this change in pH as a comparative measure to calculate number of Cu(2+) ions in the solution?

Chemosynthesis - 6-2-2015 at 21:38

I'm kind of curious why you posted this an hour after your last reply in this duplicate thread: https://www.sciencemadness.org/whisper/viewthread.php?tid=61...

While the original post probably does belong in Beginnings rather than Chemistry in General, cross-posting violates guideline 9:"Avoid cross-posting or double-posting: Cross-posting is posting similar topics or replies in different forum sections or threads in order to call for attention or for other reasons. The only attention that this calls for is the attention of the moderators. Double-posting is posting a sequence of replies one after another in the same thread. The forum has an edit function that can be used to add or modify the text of your recent replies, so use this function instead of double-posting."
https://www.sciencemadness.org/whisper/viewthread.php?tid=19...

Chemosynthesis - 7-2-2015 at 14:31

What is the source of your water for each solution? Are they all the same? Experimental error, such as equilibration of atmospheric CO2 and carbonic acid in your water source, or distillation flaws which carry over some compounds/ions may come into play. When doing work that is ion sensitive, my protocols tend to specify using distilled, deionized water. Sometimes the source (tap or container) matters.

Also, what kind of glass? You are dipping a microscope slide into CuCl2 solution and trying to only retain the Cu2+ In your initial dip? I am not familiar with the actual ion substrate, as there can be many to choose from in ion exchange chromatography. I can only presume this is the case in your experiment as well. This is what I believe blog fast was asking.

[Edited on 7-2-2015 by Chemosynthesis]

edwin - 7-2-2015 at 17:43

I am using double distilled water as solvent.
And the substrate is microscopic glass slide, cleaned with soap water, single distilled water, acetone, then double distilled water.

blogfast25 - 7-2-2015 at 18:19

Quote: Originally posted by edwin

I am using double distilled water as solvent.
And the substrate is microscopic glass slide, cleaned with soap water, single distilled water, acetone, then double distilled water.

It's likely you need some 'primer' or 'sensitizer' solution, to promote adherence of copper ions to the glass.

In silver mirroring, a stannous chloride solution is used to rinse the glass and after rinsing with water promote adherence of the silver metal to the glass.

I'm not claiming that stannous chloride would work for your application, I simply do not know that.

A fairly alkaline 'primer' solution might be worth considering. Any residual alkali that's not completely washed off on rinsing, would on treatment with CuCl2 solution probably cause particles of Cu(OH)2 to adhere to the glass. On treatment with a sulphide the Cu(OH)2 would convert to CuS quickly. It's just an idea.

If you do manage to make some of the copper ions adhere to the glass, converting them to CuS then becomes the easy part.

[Edited on 8-2-2015 by blogfast25]

edwin - 8-2-2015 at 00:34

Thank you sir,

I will try it.

blogfast25 - 8-2-2015 at 08:00

Feedback on any progress would be appreciated by several here, I think.

Other approaches could be the use of a weak HF glass etching solution as a 'primer' or silane functionalised copper complexes:

[Cu2+ - f] + glass === > [Cu2+ - f - glass]

[Cu2+ - f - glass] + S2- === > CuS + f + glass

[Edited on 8-2-2015 by blogfast25]