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Topic: Effect of ethanol on the shape of crystals  (Read 27534 times)

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Offline Rabn

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Re: Effect of ethanol on the shape of crystals
« Reply #15 on: December 24, 2007, 09:49:17 PM »
How is the state of the equilibrium affected after adding NaCl?

Offline Mitch

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Re: Effect of ethanol on the shape of crystals
« Reply #16 on: December 25, 2007, 03:39:27 AM »
It'll push solutes out of the water phase.
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Offline Hunt

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Re: Effect of ethanol on the shape of crystals
« Reply #17 on: December 25, 2007, 02:16:50 PM »
Mitch I did not get your point.

How to know whether a complex molecule is soluble in water or not ? For binary salts, there are certain solubility rules that serve for qualitative purposes. Is there anything like that for coordination compounds?

For clarity my question should have been,

Does precipitation occur at all between Cl- and [Cu(NH3)4]2+ ?
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But what if NaCl is added, would the ppt be  [Cu(NH3)4]Cl2(s)  ?

Offline Mitch

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Re: Effect of ethanol on the shape of crystals
« Reply #18 on: December 25, 2007, 02:25:39 PM »
in general, salt pushes other solutes out of water. I have no clue whether your complex is soluble in water, I'm just stating a common principle of adding salt to solutions.
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Offline Rabn

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Re: Effect of ethanol on the shape of crystals
« Reply #19 on: December 25, 2007, 10:56:37 PM »
I wonder if that complex with Cl(-) would even exist. If that complex does exist I'm sure that there is a Ksp associated with it. You should do a literature to see if it does exist. I say this because Cu's electron configuration with the four NH3 coordinated to it has a favorable half full D-shell. Cl has such a high electronegativity that it would form an ionic type bond to the complex. But as we know ionic Cl bonds usually dissociate in aqueous solutions.  So I don't think the Cl(-) complex would actually exist as a ppt. You would definitely need to do some search through literature. My guess is that adding NaCl would precipitate CuCl2 but the amount would be affected by the pH of the solution, which would become basic.

Offline Borek

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Re: Effect of ethanol on the shape of crystals
« Reply #20 on: December 26, 2007, 07:20:25 AM »
Copper (II) chloride solubility is in the range of 45 g (mass of anhydrous salt) per 100 g of H2O (solution density well over 1.2). You may convert that to Kso, although saturated solution has a high ionic strength (around 16), so take the number obtained with a grain of salt. That's not a sparringly soluble salt, thats why Kso is not listed in tables. What was amount and concentration of HCl added?

My guess is that adding NaCl would precipitate CuCl2 but the amount would be affected by the pH of the solution, which would become basic.

Please elaborate - why do you expect pH to rise after NaCl addition?
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Offline Rabn

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Re: Effect of ethanol on the shape of crystals
« Reply #21 on: December 26, 2007, 12:25:00 PM »
I suspect a pH rise because some of the released NH3 ligands would surely become NH4+ which would increase the [OH-].

Offline Borek

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Re: Effect of ethanol on the shape of crystals
« Reply #22 on: December 26, 2007, 02:08:48 PM »
That'll be possible only if Cl- will either remove NH3 from the complex (with stablility constants of Cu2+/Cl- complexes around 1 it aint gona happen) or if the CuCl2 precipitates - not very likely with so high solubility.
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Offline Rabn

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Re: Effect of ethanol on the shape of crystals
« Reply #23 on: December 26, 2007, 02:48:52 PM »
Thanks for making me double check myself Borek. I mistakenly looked at the Ksp of Copper(I) Chloride. Which in effect made me contradict myself. I'm curious about these stability constants you mentioned. I haven't run into those in my studies(I haven't taken any advanced inorganic/organic courses yet).  I'm going to do a search for some info, if you know of any good sites describing those would you mind posting a link?

Offline Borek

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Re: Effect of ethanol on the shape of crystals
« Reply #24 on: December 26, 2007, 03:36:35 PM »
I have several books with different aqueous equilibrium constants collections; however, these are mostly published in Eastern Europe back in seventies/eighties so they will be mostly likely out of reach for you.
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Offline Hunt

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Re: Effect of ethanol on the shape of crystals
« Reply #25 on: December 28, 2007, 05:07:53 AM »
Mitch , nevermind
Borek , the experiment was qualitative.

Quote from: Borek
What was amount and concentration of HCl added?

Offline AWK

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Re: Effect of ethanol on the shape of crystals
« Reply #26 on: December 28, 2007, 06:08:22 AM »
Stability constants for copper(II) ammonia system are given in Journal of Chemical Education 82(3) 408-14 (2005)
A.R. Johnson, T.M McQuinn, K.T. Rodolfa
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Offline Borek

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Re: Effect of ethanol on the shape of crystals
« Reply #27 on: December 28, 2007, 06:44:12 AM »
Borek , the experiment was qualitative.

Still, there is completely different picture between adding 1mL of 1M HCl and 5mL of 35% HCl... I am not asking about exact numbers, rather about orders of magnitude.
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Offline Hunt

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Re: Effect of ethanol on the shape of crystals
« Reply #28 on: December 28, 2007, 07:49:28 PM »
It wasn't more than 1 ml of HCl in a test tube, its concentration might have been 1 or 2 M. I cant really remember.

Is there any possibility that hydrogen gas was emitted during the process?

Offline AWK

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Re: Effect of ethanol on the shape of crystals
« Reply #29 on: December 31, 2007, 01:09:06 AM »
Is there any possibility that hydrogen gas was emitted during the process?

Did you try writing down a balanced reaction?
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