Iron (III) Chloride

[jowrose]

I recently made some Iron (III) Chloride by placing an iron nail in a solution of hydrochloric acid. The resulting solution was yellow, which is odd because I read somewhere that the iron chloride solutions were usually brown. So I decided to boil the solution in hopes of obtaining iron chloride as a solid. This solid came out a much darker brown.

 

Did I do something wrong? Did another reaction occur as I heated the solution? Or do I really have a solid sample of FeCl3?

[xeluc]

All of my Iron (III) Chloride solution have always been yellow. This is the correct color. Either Iron Chloride can be brown also, or it is caused by impurities such as Oxide, Hydroxide. Regardless, you have done nothing wrong.

[jowrose]

Thanks. I'm glad i'm not screwing anything up...

 

By the way, I read somewhere that iron chloride can be used to etch metal. How would this be done? It would only work with more reactive metals, right? Aluminum, Zinc, etc?

[jowrose]

Does anyone know what solid Iron (III) Chloride looks like? I boiled some solution down, and it turned out a sort of light purple/brown powder. Is this true Iron (III) Chloride?

[woelen]

Solid iron (III) chloride has a mustard-like yellow/brown color. The stuff you buy at electronics stores is the hexahydrate, FeCl3.6H2O.

 

Solutions of FeCl3.6H2O are yellow, when acidified. They become brown when not acidified, due to hydrolysis of the iron (III) and subsequent formation of hydroxo-complexes of iron (III).

 

When you boil down a solution of ferric chloride in water, then you'll end up with some basic compound. On heating it looses HCl and you end up with a ferric compound, containing chloride, but also hydroxide.

 

Iron (III) chloride is a good printed circuit board etchant and is sold as such in electronics parts stores. It dissolves copper with ease, especially if a small amount of hydrochloric acid is added. It is quite specific for dissolving copper. Dissolving other metals is much more combersome.

The reason for this is quite complex. Ferric chloride forms the complex ion FeCl4(-), which is a reasonable oxidizer, but equally important is that copper (II) formed is complexed by the chloride:

 

2FeCl4(-) + Cu --> 2Fe(2+) + CuCl4(2-) + 4Cl(-)

[jowrose]

So when I boil down dissolved Iron (III) Chloride I'm not going to end up with a pure solid? How would it also contain hydroxide?

 

forgive me, I'm a high school chemistry student with a miserable lack of knowledge...

[xeluc]

When you boil the FeCl3, it heats up and hydrolyzes. Meaning, a water molecule's hydroxide ion is taken by the Iron. Fe3+ + 3Cl- + 3H2O --> Fe(OH)3 + 3H+ + 3Cl- The hydroxide darkens the liquid. If you evaporate the solution with a dessicant such as Calcium Chloride, you will find that your solution stays more pure.

[jowrose]

So the chlorine is lost when I heat up the Iron (III) chloride? hmmm. If I end up with iron hydroxide, is that not the same thing as "rust acid"? I believe that is the product of putting an iron nail on the negative electrode of an electrolysis reaction.

[[w00t]]

Doesnt Iron Hydroxide turn in to Iron Oxide when its heated?

[RyanJ]

'']Doesnt Iron Hydroxide turn in to Iron Oxide when its heated?

 

 

Yes it does

 

Cheers,

 

Ryan Jones

[[w00t]]

Let me see if i have it right;

I have a cup with saltwater, 2 iron nails and a 18vdc adaptor.

So what im thinking is, you strip down the positive wire and the negative and you tie one wire on to one nail, and you tie the other one on the other nail.

Stick it in the saltwater, one of the nails being Positive starts bubbling....

So after say 1 hour i would have all these brown/greenish stuff floating around. So now i would try to evaporate the water by heating it and the results would be iron oxide right? what i got was some brownish/red powder.

 

sorry if this is offtopic.

[woelen]

So the chlorine is lost when I heat up the Iron (III) chloride? hmmm. If I end up with iron hydroxide, is that not the same thing as "rust acid"? I believe that is the product of putting an iron nail on the negative electrode of an electrolysis reaction.

You will not end up with pure iron hydroxide. What Xeluc states is an extreme form of the hydrolysis reaction. In reality you'll end up with a compound, which is best described by

 

[math]FeCl_{x}(OH)_{3-x} . yH_2O[/math]

 

Here x is a (possibly non-integer) number between 1 and 3 and y is some (possibly non-integer) number. This compound is a bad non-stoichiometric compound, whose precise composition hardly can be determined. That depends on how fast it is heated, the amount of HCl present in the liquid, humidity of the air, etc.

[YT2095]

woot, now apply the above to all the Chlorate and sodium side reactions too, and you`ll see that the product you end up with is a real mess.

any free chlorine liberated that reacted with the iron would soon be displaced by the sodium ions too.

 

filtering out the insolubles would leave an iron product though, so it`s not a BAD method for extracting Iron from Steel for instance

in fact I`ve used a similar method quite recently to extract Tin (Sn) from Solder.

[jowrose]

I know the electrolysis creates relatively pure Iron Oxide (for thermite...) when you attach it to the positive wire, but what if you attach the nail to the negative? Do you get Iron Hydroxide? And if the hydroxide is lost when the substance is heated, ending with Iron oxide, it seems that that method is far more efficient at creating iron oxide than simply attaching the nail to the positive end (as is commonly done).

 

So if the hydroxide is lost with heating, then when I stick an iron nail in HCl and receive iron chloride and heat that substance, what will the product be?

 

jeebus i'm confuzzled

[YT2095]

you`ll find that the cathode remains largely unaffected anyway, using it doesn`t Really make the cell more efficient, it only precludes other cathode contaminats.

the red iron oxide will not dissolve in HCl, so it really all depends what species you mean when you say iron oxide

[jowrose]

ok, that makes sense. completely off topic, how is Fe3O4 a compound? is the extra oxygen loosely attached, which is what makes it so magnetic?

 

So i took that compound from the Iron - HCl reaction that I boiled off of the solution and put that in a crucible and heated it up. A few minutes later, it started reacting and for a good 45 seconds it was emitting thick brown smoke, with a small amount of yellow vapor at the bottom of the crucible being released as well. Was this the chlorine leaving the iron? Did I really have Iron (III) Chloride that I boiled down? Or was I oxidizing something?

[woelen]

ok' date=' that makes sense. completely off topic, how is Fe3O4 a compound? is the extra oxygen loosely attached, which is what makes it so magnetic?

 

So i took that compound from the Iron - HCl reaction that I boiled off of the solution and put that in a crucible and heated it up. A few minutes later, it started reacting and for a good 45 seconds it was emitting thick brown smoke, with a small amount of yellow vapor at the bottom of the crucible being released as well. Was this the chlorine leaving the iron? Did I really have Iron (III) Chloride that I boiled down? Or was I oxidizing something?[/quote']

No, chlorine cannot be driven off as element. Chlorine is not a thick brown smoke, it is a pale and clear light green gas.

 

http://woelen.scheikunde.net/science/chem/compounds/chlorine.html

 

The thick brown smoke is a mix of fumes of HCl, water vapor and some FeCl3, which is driven off. You must have heated it very hot , otherwise you certainly would not have had the brown smoke. Be careful with what you do, breating a lot of metallic salts/compounds is not fun at all.

 

Remember, you never get elemental chlorine in this way. You only get chloride, not chlorine.

[jowrose]

It couldn't have been that hot, I was only using an alcohol burner and a crucible. I do have a blowtorch, but I only use that for the funner (and more dangerous) stuff (heating salt to make sodium). And yes i know funner is not a word.

 

How would there be any HCl left? If HCl is a gas, is it just loosely trapped in the solid compound I was heating?

 

That picture of Cl2 you posted the link to looks a lot like what was forming at the bottom of the crucible (not the brown smoke). It seemed a little darker (more greenish yellow) though.

[woelen]

It couldn't have been that hot' date=' I was only using an alcohol burner and a crucible. I do have a blowtorch, but I only use that for the funner (and more dangerous) stuff (heating salt to make sodium). And yes i know funner is not a word.

 

How would there be any HCl left? If HCl is a gas, is it just loosely trapped in the solid compound I was heating?

 

That picture of Cl2 you posted the link to looks a lot like what was forming at the bottom of the crucible (not the brown smoke). It seemed a little darker (more greenish yellow) though.[/quote']

In the solid compound you do not have any HCl at all. It is formed on heating. The solid compound is approximately FeCl3.6H2O and what happens is that the water molecules are broken down. A somewhat better description of your solid compound is Fe(OH2)6Cl3, the OH2 groups (water) loose a H(+) on heating and these combine with a Cl(-) ion to give HCl which escapes as (colorless but fuming) gas.

 

With an alcohol burner and a crucible you also can reach fairly high temperatures (several hundreds of degrees centigrade) and that is enough to ctreate the smoke.

 

The yellow vapor most likely is FeCl3, mixed with HCl and H2O, which somewhat higher up cools down and gives fumes, where is looks like smoke.

 

If you also had a strong smell of chlorine, then I believe that some chlorine is released, but I have severe doubts on that.

[jowrose]

hmmm so I would be left with an iron hydroxide solid? Is there a way to dissolve off the water of the Iron (III) Chloride solution and be left with an Iron (III) Chloride solid?

[woelen]

You cannot make anhydrous ferric chloride from the hydrous salt. This is the case for MANY hydrated salts, most notably those of iron (III), aluminium and chromium (III), but also for almost all nitrates. All these salts decompose on heating, loosing acid and leaving behind an oxide, hydroxide or basic salt (which is mixed hydroxide/oxide and the original ion).

 

A few chlorides can be obtained in the anhydrous state from their hydrated salts, e.g. CuCl2 and CoCl2.

 

This problem with dehydration also is the reason, why the stuff you buy at electronics stores for etching PCB's is not FeCl3, but FeCl3.6H2O.

 

Making anhydrous FeCl3 can only be done by heating the hydrated salt carefully in a stream of dry HCl or by burning iron in dry Cl2-gas.

 

Another nice example of such an elusive anhydrous salt is Cu(NO3)2. From aqueous solution you get Cu(NO3)2.3H2O, a nice blue crystalline solid (I actually have some of that salt lying around and it looks nice). When this is heated, HNO3 is formed and CuO remains. The HNO3 is decomposed further at the high temperatures involved, giving water, oxygen and nitrogen oxides. People, however, have succeeded in making anhydrous Cu(NO3)2, which is a volatile blue compound, it is not a salt. It was prepared by dissolving Cu-metal in liquid NO2 and carefully allowing the NO2 to evaporate. This gives a solvated salt Cu(NO3)2.2NO2, which on heating at 80 degrees C slowly looses its NO2 without decomposition of the Cu(NO3)2. You see, not something to be done at home.

[jowrose]

yeah, I've used copper nitrate tri-hydrate (i think that's how you say it) in chemistry class, it does have a really nice color. How would I go about making iron (III) chloride something-hydrate? wait for evaporation of all the water, by spreading out on a thin sheet or something?

[xeluc]

Yes, you already explained how to make FeCl3.6H2O in your first post. Letting it evaporate works kind of. FeCl3 is EXTREMLY hygroscopic. I havn't been able to get a dry compound by evaporation. Dessicants such as CaCl2 which can be found in any hardware store as painter's dessicant would be the way to go. Get a large jar, fill with CaCl2, set a dish of FeCl3 solution on top, seal, and wait. Heating may be possible, but I'm not sure how stable FeCl3 is.

[jowrose]

You can reuse the CaCl2, right? Because it simply acts as a catalyst of sorts?

[xeluc]

catalyst... no... The CaCl2 plays no part in any reaction. you do not mix the FeCl3 and CaCl2.. You keep them seperate and the CaCl2 sucks out the water throguh the air.. But I do beleive the CaCl2 is reusable, jsut heat it up to let go of the water.