Sciencemadness Discussion Board - Troubles with Crystals

Troubles with Crystals

aga - 16-5-2015 at 13:32

I've been trying to make crystals of FeCl₂ for a few days and have failed dismally.

Procedure has been to react steel wool with 20% HCl for a day or so (ambient temperature has been 25+ in daytime) filter off the lime green liquid, then scratch my head for a while.

Leaving exposed to Air to evaporate simply made FeCl₃ fairly quickly (a few hours).

Boiling off the water resulted in FeCl₃.

Boiling at 28 mbar vacuum, 65~75 C did just about the same thing.

Each time i have to add more iron to reduce the Fe back to +2.

Intensive googling turned up CHRIS25's post on SM, yet he didn't say how he arrived at crystals.

Anyone any ideas ?

Texium - 16-5-2015 at 13:44

That's something that I've wanted to do for a while too. I also tried all of the stuff that you have without success. I have however successfully let FeSO₄ crystallize in air out of a large volume of a partially oxidized solution. It will crystallize out before the Fe₂(SO₄)₃ apparently, forming well-formed fairly pure crystals of FeSO₄ on the bottom. The solution seems to protect the crystals from the air. A quick rinse with cold water will clean them up nicely. I don't know if the same method would work with FeCl₂. I haven't tried using a large enough volume of solution to test it out.

These crystals were formed in that method. Bad picture, but you get the idea.

aga - 16-5-2015 at 13:53

Hmm.

So seeing as FeCl₃ is 92g/100ml and FeCl₂ is 68.5g/100ml the idea is to Let the stuff oxidise in a certain volume of water so that the FeCl₂ just has to crystallise out.

I like it and can feel a spreadsheet full of stoichimetry about to happen.

This is starting to have an Al Sulph feel to it.

Thanks zts !

blogfast25 - 16-5-2015 at 14:16

Acc. Wiki solubility table (http://en.wikipedia.org/wiki/Solubility_table#I), the solubility of FeCl2 is about twice as high hot than cold.

Use 33 % HCl and calculate the amount of iron you need to dissolve in it to equal or exceed the hot solubility limit of FeCl2. Dissolve while simmering under reflux. On cooling/chilling, about half of the product will crystallise out. First hand experience, BTW.

Simples.

[Edited on 16-5-2015 by blogfast25]

aga - 16-5-2015 at 14:28

I'll take 1st hand experience over Wiki any day.

Cheers Obi-One-K'Blogfast !

blogfast25 - 16-5-2015 at 14:35

Quote: Originally posted by aga

I'll take 1st hand experience over Wiki any day.

Cheers Obi-One-K'Blogfast !

Incidentally, in acid conditions the oxidation of FeCl2 to FeCl3 is much slower than people often believe. See also Chris' attempts to prepare FeCl3 by air oxidation of FeCl2 solutions: impractically slow (my own experience too). O<sub>2</sub> is a powerful yet sluggish oxidiser.

In near-neutral/alkaline conditions the oxidation is favoured strongly by the formation of highly insoluble Fe(OH)3. The Standard Reduction Potentials of Fe(+3)/Fe(+2) in those respective conditions reflect that, BTW. Not all our Magik Books are wrong!

[Edited on 16-5-2015 by blogfast25]

aga - 16-5-2015 at 15:10

Aha!

Keep some of the HCl unreacted !

U reekah. I reekah. Someone reekah.

blogfast25 - 16-5-2015 at 15:25

Quote: Originally posted by aga

Aha!

Keep some of the HCl unreacted !

U reekah. I reekah. Someone reekah.

Final pH no higher than about 4.

aga - 17-5-2015 at 01:24

Some calculations this morning show that under 22.3% HCl concentration, the acid brings in too much water for the FeCl₂ to crystallise - there's simply too much water.

At 33% conc the numbers work nicely, as you said.

I only have 20% HCl on hand, so will try Plan B which is to reduce back from FeCl₃.

Knowing the solubility factors, there's a chance it will work.

Amos - 17-5-2015 at 06:00

The way I circumvent the issue of preparing FeSO4 without oxidation is by instead preparing it via a single replacement reaction of steel wool with copper(II) sulfate. Using excess steel wool results in a pale green solution that is free of any added acid, which can be very easily boiled down without any noticeable oxidation occurring.

So perhaps CuCl2 could be reacted with steel wool to prepare a very stable solution of FeCl2 that could also be boiled down and crystallized in this manner, perhaps in a container like a Florence flask or a mostly covered beaker that would limit the entry of oxygen.

blogfast25 - 17-5-2015 at 06:08

Quote: Originally posted by Amos

The way I circumvent the issue of preparing FeSO4 without oxidation is by instead preparing it via a single replacement reaction of steel wool with copper(II) sulfate. Using excess steel wool results in a pale green solution that is free of any added acid, which can be very easily boiled down without any noticeable oxidation occurring.

Nah. Get some garden grade FeSO4 hydrate, dissolve to hot saturation, filter and cool to crystallise. Don't waste any copper salts on this, IMHO.

Amos - 17-5-2015 at 06:10

Quote: Originally posted by blogfast25

Quote: Originally posted by Amos

Nah. Get some garden grade FeSO4 hydrate, dissolve to hot saturation, filter and cool to crystallise. Don't waste any copper salts on this, IMHO.

I know it's expensive, but I actually value the copper powder that I obtain as a byproduct, as it's much easier to react it with, say, acetic acid, than copper wire would be.

blogfast25 - 17-5-2015 at 06:14

Quote: Originally posted by Amos

I know it's expensive, but I actually value the copper powder that I obtain as a byproduct, as it's much easier to react it with, say, acetic acid, than copper wire would be.

So you're preparing copper powder with FeSO4 as a by-product!

Amos - 17-5-2015 at 06:16

And if I wasn't out of steel wool, I could be making copper powder with a byproduct of iron(II) chloride right now!

aga - 17-5-2015 at 14:08

No joy with Plan B.

The filter paper dissolved, so i may have an alternate method to dissolve cellulose.

Back to Plan B(logfast) which means stuffing my 20% with HCl gas to get it up to 33% at least.

Edit:

Amazingly i do not need to look up any references or buy any new reagents or glassware to do that safely (kinda) nor do i need to look anything up to titrate the acidity of the resulting solution.

Learning is a wonderful experience.

A Big Thank You to all concerned for their valued inputs over this first year of my chem learning.

[Edited on 17-5-2015 by aga]

blogfast25 - 17-5-2015 at 15:16

Yep, filter paper doesn't resist hot HCl very well. But bear in mind you may have to filter with your 33 % HCl too. Might want to invest in a high porosity glass frit filter + vacuum for jobs like that... 'Acid resistant' paper also exists but I'm not sure just how acid resistant it actually is.

Or think non-woven glass fibre, several layers thick.

[Edited on 17-5-2015 by blogfast25]

Praxichys - 18-5-2015 at 10:55

I have had great luck filtering with nonwoven (felted) PET material. It is very cheap, reusable, and resists many things that ordinary filter paper does not.

It is commonly sold as "recycled plastic weed block" for gardens. They also make polypropylene weed block but it is more expensive. I have found cheap shopping bags made of the stuff. You can also get it at the local craft store/sewing shop.

http://www.ebay.com/itm/Premium-Non-woven-Fabrics-Shopping-C...

These bags appear to be made out of it. For $3.66, you get 10 bags delivered! It is used in the airbag industry for breakaway wraps and tethers, so I have some from where I work.

blogfast25 - 18-5-2015 at 11:34

Quote: Originally posted by Praxichys

I have had great luck filtering with nonwoven (felted) PET material. It is very cheap, reusable, and resists many things that ordinary filter paper does not.

It is commonly sold as "recycled plastic weed block" for gardens. They also make polypropylene weed block but it is more expensive. I have found cheap shopping bags made of the stuff. You can also get it at the local craft store/sewing shop.

http://www.ebay.com/itm/Premium-Non-woven-Fabrics-Shopping-C...

These bags appear to be made out of it. For $3.66, you get 10 bags delivered! It is used in the airbag industry for breakaway wraps and tethers, so I have some from where I work.

Interesting. Thanks for sharing.