Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1  2
Author: Subject: Preparation of Ammonium iron (III) sulphate (ferric alum)
MrHomeScientist
International Hazard
*****




Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline

Mood: No Mood

[*] posted on 12-12-2013 at 15:12


Got some photos of my crystals for your viewing pleasure!

My ferric ammonium sulfate was purchased from Sigma Aldrich something like 15 years ago. It appears in the bottle as lavender chunks. (Photo 1)

I dissolved some in water as detailed in my post above back in October and left it in the fume hood to see what it would do. Just last week I checked on it and gorgeous large crystals had grown! I harvested the largest from the liquor and some were very well formed. The largest was unfortunately plagued with lots of parasitic small crystals. (Photo 2)

I placed three of the better formed crystals back in the solution to continue growth. You can see the rich brown color of the solution, completely clear with no iron hydrolysis evident. We'll see how it goes! (Photo 3)

1.jpg - 126kB 2.jpg - 140kB 3.jpg - 134kB
View user's profile Visit user's homepage View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 13-12-2013 at 11:05


Very nice indeed, MrHS.

Years ago I read that growers of really macro crystals (of alums), like 2" or more, actually cheat by gently filing (or sanding) off the parasitic ones! Sound plausible to me: once a crystal fault line has developed there's no cure, well... other than filing off the side growth.

Re. hydrolysis, the brown colour is due to Fe(OH)<sup>2+</sup>, which would be the first step to Fe(OH)<sub>3</sub>. But here acidity and concentration of Fe(III) prevent it from going all the way.

[Edited on 13-12-2013 by blogfast25]




View user's profile View All Posts By User
DraconicAcid
International Hazard
*****




Posts: 4288
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline

Mood: Semi-victorious.

[*] posted on 13-12-2013 at 11:42


Impressive. I can never get nice crystals like that, even from something as simple as alum.



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.
View user's profile View All Posts By User
MrHomeScientist
International Hazard
*****




Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline

Mood: No Mood

[*] posted on 16-12-2013 at 07:28


Thanks! I had actually forgotten about them for a while, growing in the back of the hood. Apparently it's the perfect environment for slow crystal growth!


Thinking about it this weekend, I had an idea: What about growing my large crystal on a teflon stage? I.e. put a disk of teflon in the beaker that the large crystal will sit on. Would teflon resist formation of new crystals?

If not teflon, what about a hydrophobic surface? I have some Never Wet that I've been playing with. If the solution can't get to the surface, maybe that would prevent new crystals from growing.

Any other ideas to prevent these little crystals from growing where I don't want them?
View user's profile Visit user's homepage View All Posts By User
Poppy
Hazard to Others
***




Posts: 294
Registered: 3-11-2011
Member Is Offline

Mood: † chemical zombie

[*] posted on 16-12-2013 at 11:13


Mr Home Scientist, I think those big crystals are nothing but a chunk of ammonium sulphate that has went out separately!
You can compare sizes and color or even redissolve those if you please and tell us if anything might have ended bad again!
View user's profile View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 16-12-2013 at 14:42


Quote: Originally posted by Poppy  
Mr Home Scientist, I think those big crystals are nothing but a chunk of ammonium sulphate that has went out separately!
You can compare sizes and color or even redissolve those if you please and tell us if anything might have ended bad again!


Utter nonsense. If you start from ferric ammonium alum you end up with ferric ammonium alum.




View user's profile View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 16-12-2013 at 14:47


Quote: Originally posted by MrHomeScientist  
Thinking about it this weekend, I had an idea: What about growing my large crystal on a teflon stage? I.e. put a disk of teflon in the beaker that the large crystal will sit on. Would teflon resist formation of new crystals?

If not teflon, what about a hydrophobic surface? I have some Never Wet that I've been playing with. If the solution can't get to the surface, maybe that would prevent new crystals from growing.



I don't really see how sitting them on a hydrophobic surface would prevent solution from getting to the [crystal] surface. Even if you did achieve the latter, you wouldn't get any crystal growth at all there.




View user's profile View All Posts By User
MrHomeScientist
International Hazard
*****




Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline

Mood: No Mood

[*] posted on 17-12-2013 at 11:43


Quote: Originally posted by blogfast25  
I don't really see how sitting them on a hydrophobic surface would prevent solution from getting to the [crystal] surface. Even if you did achieve the latter, you wouldn't get any crystal growth at all there.

Well that's the idea though. Place a hydrophobic or teflon surface in a beaker, place one of my large crystals on that, and fill the beaker with ferric alum solution. This way the large crystal will grow, but no small crystals will start growing elsewhere on the surface since there'd be no other nucleation sites. That's the thought, at least.
View user's profile Visit user's homepage View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 17-12-2013 at 12:40


Hydrophobic really means 'high surface tension' but even the highest surface tension is overcome by modest hydrostatic pressure, for instance a Teflon beaker still fills with water.

I personally don't see how a hydrophobic resting surface for the crystals could prevent side growths.

How about weightlessness? All these balls of ferric ammonium sulphate solution with crystals in them, floating about in a space station? The sky is the limit, no? ;)

[Edited on 17-12-2013 by blogfast25]




View user's profile View All Posts By User
MrHomeScientist
International Hazard
*****




Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline

Mood: No Mood

[*] posted on 17-12-2013 at 14:22


I see, thanks for the responses.

If anyone knows of any methods to prevent these extra crystals from growing I'd be interested to hear about them. Space station would be ideal!

Barring that, I know some people suspend the crystal in the solution to avoid parasitic growths. But I can't think of how to do that without ruining the formation process around whatever string holds it up, and then trapping the string inside the crystal for all to see. I'd think even fishing line would be visible, unless it happens to match the material's index of refraction perfectly.
View user's profile Visit user's homepage View All Posts By User
Poppy
Hazard to Others
***




Posts: 294
Registered: 3-11-2011
Member Is Offline

Mood: † chemical zombie

[*] posted on 19-12-2013 at 21:16


Quote: Originally posted by blogfast25  
Quote: Originally posted by Poppy  
Mr Home Scientist, I think those big crystals are nothing but a chunk of ammonium sulphate that has went out separately!
You can compare sizes and color or even redissolve those if you please and tell us if anything might have ended bad again!


Utter nonsense. If you start from ferric ammonium alum you end up with ferric ammonium alum.

I just don't know but my method yielded much purplish samples, so how about no?
View user's profile View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 20-12-2013 at 05:41


Poppy:

We know ferric ammonium alum comes in two colour variants but we don't really know why (it's been discussed elsewhere here). The colourless crystals in MrHS sample are FAA too, not ammonium sulphate.

[Edited on 20-12-2013 by blogfast25]




View user's profile View All Posts By User
MrHomeScientist
International Hazard
*****




Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline

Mood: No Mood

[*] posted on 20-12-2013 at 12:09


Update

I took my crystals out of the growing solution Friday of last week, since I wouldn't be around to check on them over the weekend. I returned Wednesday and found they had discolored - turning significantly brown!

1.jpg - 187kB

I put the nicer, large crystals back into solution and covered the beakers with Parafilm. I didn't want any more growth, I just wanted to see if "rehydrating" them would solve the problem. To my relief, it did. Two days later, my large crystals have returned to their previous transparent lavender color. Had me worried for a minute there! I wasn't aware these crystals would be air-sensitive.
View user's profile Visit user's homepage View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 21-12-2013 at 06:19


Years ago I saw a sample of a large FAA crystal (about 2"), in a museum. Years of exposure to dry air had eroded the surface considerably, even though it had been varnished to prevent that!

Just keep your samples in a closed container and they should preserve indefinitely.




View user's profile View All Posts By User
rey31tjia
Harmless
*




Posts: 1
Registered: 31-10-2017
Member Is Offline

Mood: No Mood

[*] posted on 31-10-2017 at 02:53


Quote: Originally posted by kmno4  
Yes, I confirm this procedure. FeSO4 + H2SO4 + H2O2 + (NH4 )2SO4 really works fine.
I used to make larger amount ( ~ 200g) of this alun.
Indeed, from deep brown solution small white crystals are formed.
On the picture - mentioned alun.
It is almost coloreless, with a little amethyst (~violet) shade.
ps. my fellow made (in similar way) beautiful, large (> 1 cm), bright violet crystals of Fe(III) sulfate ( x 9 H2O).
ps2. with aid of ~5% acidic solution of K3[Fe(CN)6] you can test presence of Fe(II) in your oxidated solution. When Fe(II) ions are present, deep blue colour/precipitate appears when you mix ferricyanide sol. with tested sol. It is very sensitive test. When only Fe(III) ions are present, mixing gives clean brown solution.

[Edited on 8-9-2008 by kmno4]


How did you crystallize it? Did you refrigerate the solution? Please help me..
Thank you..
View user's profile View All Posts By User
jamit
Hazard to Others
***




Posts: 375
Registered: 18-6-2010
Location: Midwest USA
Member Is Offline

Mood: No Mood

[*] posted on 28-7-2023 at 17:43


so I followed the synthesis of blogfast25 and I obtain violet crystals but they oxidize so quickly to light brown with in 10 hrs and they are sticky? did i do something wrong? has anyone also had this problem making ferric alum.

I dissolved ferrous sulfate and acidified it with sulfuric acid. Then I oxidized it with peroxide until the effervescence ceased. I then added solution of ammonium sulfate and mixed the two solutions together.

Then I filtered and heating to remove some liquid and allowed it to evaporate until lilac crystals form. but the ferric alum oxidizes back to light brown color within 6-10 hrs while drying and they are really sticky. help!!
View user's profile View All Posts By User
Fery
National Hazard
****




Posts: 993
Registered: 27-8-2019
Location: Czechoslovakia
Member Is Offline


[*] posted on 29-7-2023 at 10:28


jamit you did very nice experiment
I did the same as you did
I remember that I used slight excess of H2SO4
I think the color change into orange it is not any oxidation, but it is losing of crystalline water or absorbing air moisture
pure crystals are almost colorless, very very very pale violet, I have a vial with them which I synthesized 30 years ago and they are still good quality (but the cap is also sealed with wide rubber band)
water solution and crystals with lost crystalline water have orange color
very interesting how almost colorless crystals are formed from such orange colored solution
View user's profile Visit user's homepage View All Posts By User
Bedlasky
International Hazard
*****




Posts: 1224
Registered: 15-4-2019
Location: Period 5, group 6
Member Is Offline

Mood: Volatile

[*] posted on 29-7-2023 at 12:01


Jamit: The colour change is due to loss of water, not due to oxidation. Ammonium ferric sulfate is violet because it contains violet [Fe(H2O)6]3+ ions in it's crystalline structure. If some water is lost, sulfate coordinates on to Fe(III) an these complexes are brown in colour.

To prevent water loss, you can store crystal in saturated solution of ammonium ferric sulfate or in the paraffin oil. I keep mine in paraffin oil and it is still violet after several years. It doesn't look exactly like freshly crystallized crystal, it's paler, but it is still well preserved.

For crystal growing tips, this site is quite useful.

https://en.crystalls.info/Iron(III)-ammonium_sulfate
View user's profile View All Posts By User
 Pages:  1  2

  Go To Top