urenthesage
Hazard to Self
Posts: 77
Registered: 21-2-2016
Member Is Offline
Mood: No Mood
|
|
Chromium hydroxide?
I started with a chromium salt, the sulfate I believe and I added ammonium hydroxide trying to create chromium hydroxide which is green. Instead I
have a greyish salt with a pink liquor remaining. What have I created
? is it some wierd hydrate that is grey? is it a hexavalent compound? is it crap left over from the sulfuric acid I used to make the original salt?
|
|
|
DraconicAcid
International Hazard
Posts: 4355
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
You probably have a mixture of chromium hydroxide and an ammonia coordination complex.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
urenthesage
Hazard to Self
Posts: 77
Registered: 21-2-2016
Member Is Offline
Mood: No Mood
|
|
Thanks, though I dont know what Im going to do with it. Any ideas on turning this into a salt that isnt extremely hydroscopic?
|
|
|
Texium
|
Thread Moved
9-9-2016 at 13:25 |
Lion850
National Hazard
Posts: 517
Registered: 7-10-2019
Location: Australia
Member Is Offline
Mood: Great
|
|
I wanted to make some chromium precursor to make other chromium salts so I decided to convert some of my chromium iii nitrate into chromium carbonate
by doing a double displacement with potassium carbonate.
29g potassium carbonate was dissolved in water and poured into a solution of 56g Cr(NO3)3.9H2O in water. Instead of a chromium carbonate gas was
evolved and reading up make me think the following happened:
2Cr(NO3)3 + 3K2CO3 + 3H2O = 2Cr(OH)3 + 6KNO3 + 3CO2
The blue-green ppt was dried on a steam bath for many hours until the weight was stable. The yield was 26g, which is much more than the calculated
14.4g anhydrous. It is probably a hydrate; or maybe not even that straight hydroxide as it seems this salt is not always well defined.
Anyway, it readily dissolves in concentrated HCl so seems it will be good as a feed stock.
 
|
|
|
artemov
Hazard to Others
Posts: 181
Registered: 22-8-2018
Member Is Offline
|
|
In my synthesis of potassium dichromate from chromium metal, I used sodium carbonate (aq) on chromium sulfate (aq). Lotsa CO2 and a fluffy, hard to
settle ppt is obtained. Don't use ammonium or sodium hydroxide as you might overshoot and the ppt will dissolve again.
|
|
|
unionised
International Hazard
Posts: 5128
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Some carbonates don't exist, and Cr(III) is one of them.
If you add dilute sulphuric acid and potassium sulphate or ammonium sulphate you should be able to crystallise the alum by slow evaporation
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
