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Preparing Chrome Alum and Inhibiti Hydrogen peroxide
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Topic: Preparing Chrome Alum and Inhibiti Hydrogen peroxide (Read 7668 times)
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DQD
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Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
on:
November 09, 2011, 06:30:06 AM »
I prepare Chrome Alum from K
2
Cr
2
O
7
, pure H
2
SO
4
and Ethanol 95
o
And the question is
What is the Ethanol's effect in process ?
Which substance can Inhibiti Hydrogen peroxide while storing ?
And its mechanism ?
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #1 on:
November 09, 2011, 07:59:20 AM »
What you make is not a chrome alum. Chromic acid if anything.
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ChemBuddy
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DQD
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #2 on:
November 09, 2011, 10:19:18 AM »
It's impossible, solution after reacting has dark green color
and I have let it for 1-2 week(s), it appear crystal
I do this experiment from my text book
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #3 on:
November 09, 2011, 12:15:36 PM »
Hm, perhaps it makes sense - it guarantees correct Cr:K ratio. Interesting.
Think: why does the solution become green?
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ChemBuddy
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DQD
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #4 on:
November 09, 2011, 07:19:42 PM »
i wonder
May ethanol cause ?
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #5 on:
November 10, 2011, 02:38:52 AM »
Yes, it is because of the ethanol presence, but it is not ethanol that becomes green.
What is green in this solution? Initially the solution should be red/brown. What do you know about dichromate, especially in low pH?
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ChemBuddy
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DQD
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #6 on:
November 10, 2011, 07:14:13 AM »
Green in this solution, I guess mixture of Cr
2
(SO
4
)
3
and K
2
SO
4
cause this color
not only Cr
2
(SO
4
)
3
, which has pink color
And in low pH, I dont be sure to know about dichromate
Plz explain this problem
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #7 on:
November 10, 2011, 11:11:16 AM »
If memory serves me well Cr(III) in solutions is green as long as there are no chlorides.
I am not going to give you a direct answer. First paragraph of the wikipedia page on dichromate contains an important hint.
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ChemBuddy
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DQD
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #8 on:
November 10, 2011, 08:52:10 PM »
Um
So in low pH, It means in acid solution the unstable blue peroxo complex Chromium(VI) oxide peroxide, CrO(O
2
)
2
, is formed
CrO(O
2
)
2
is a substance which I have never learn it
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #9 on:
November 11, 2011, 05:28:23 AM »
Another hint: redox process.
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ChemBuddy
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DQD
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #10 on:
November 12, 2011, 11:40:53 PM »
I think i dont have any anwser
btw, I hear my friend explain about it
due to the strong acid hydrolysis of dichromate, the ethanol presence is inhibiti this hydrolysis
According you, Does this thing right ?
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Borek
Mr. pH
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Re: Preparing Chrome Alum and Inhibiti Hydrogen peroxide
«
Reply #11 on:
November 13, 2011, 06:09:37 AM »
It is not about hydrolysis. It is about reducing Cr(VI) to Cr(III).
I already told you almost everything, start to follow hints and learn what a redox process is.
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ChemBuddy
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