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Topic: Ion exchange separation (from [CrCl2(H2O)4]+) questions. [edited]  (Read 5282 times)

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Offline monozuki

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Hello,

The questions below relate to the separation of trans-[CrCl2(H2O)4]+, [CrCl2(H2O)5]2+ and [Cr(H2O)6]3+ from [CrCl2(H2O)4]+ ion using perchloric acid (HClO4).

1. Why is perchloric acid preferred over hydrochloric acid for eluting of transition metal complexes?

2. To separate [CrCl2(H2O)5]2+, [CrCl2(H2O)4]+ solution has been heated to 50 - 55 degrees C and immediately after water was added. Why was the solution of [CrCl2(H2O)4]+ warmed to 50 - 55 degrees? (separating trans-[CrCl2(H2O)4]+ required no heating and separation of [Cr(H2O)6]3+ required boiling by comparison).

Would really appreciate the help.
Thank you very much.

Edit:
I've actually been trying to figure it out myself for the past couple of hours.  Here's what I managed to come up with:

1. Even though both of these are strong acids, perchloric acid is preferred because it's a superacid containing the non-coordinating anion (ClO4-), whereas the Cl- anion of HCl will interact easily with the cations of trans. metals. (From what I gathered the acid is not supposed to interact with the complex, so then this would make perchloric acid preferable over HCl.)

2. For this one, I could get no real info anywhere, other than the fact that chromium(III) complexed will dehydrate when they are heated. Not even sure if it relates to this though. My best guess here is that (going by comparing the three experiments and the methods for their separation) increasing the temperature of the [CrCl2(H2O)4]+ solution helps to release the Cl- anions (because with about 50 degrees C Cl2 drops to Cl and if boiled the Cl disappears altogether), which are then replaces with water.

And that's pretty much it.

Regards,
mono
« Last Edit: November 28, 2015, 12:19:14 PM by monozuki »

Offline Babcock_Hall

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Re: Ion exchange separation (from [CrCl2(H2O)4]+) questions.
« Reply #1 on: November 28, 2015, 11:46:58 AM »
Wecome to the forum.  Please read the forum rules (red letters near the top of the page).  You must show your work before we can help you.

Offline monozuki

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Re: Ion exchange separation (from [CrCl2(H2O)4]+) questions.
« Reply #2 on: November 28, 2015, 11:57:36 AM »
Wecome to the forum.  Please read the forum rules (red letters near the top of the page).  You must show your work before we can help you.

Right, my mistake. Sorry about that. I'll edit the post above to keep it tidy.

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