Lion850
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Making Erbium Salts
** I wanted to do a long post with all the salts I did in one but I kept getting a post error. So I will now try to split it up, maybe the post is too
long **
I was interested in the different shades of pink of erbium salts, but I could not find a lot of info on erbium compounds online so decided to make
some and see which shades I get. I had 2 potential erbium sources: A single metal lump with weight 43g and some ceramic grade oxide Er2O3 (which
itself is pink). I did not want to use a lot of the oxide as it is nearly finished so decided to use the lump. The initial plan was to react the lump
with sulphuric acid, making a lot of sulphate, and then making various other erbium compounds by double displacement reactions.
I put the 43g lump in 50ml water in a beaker and slowly added 96% sulphuric acid. A vigorous reaction started with lots of bubbles (presumably
hydrogen) but it completely stopped just as fast! I then tried concentrated acid with the same result. Heating the solution to near 100C did not
restart the reaction.
After an hour or so of trying I decided that something quickly pacifies the erbium metal in sulphuric acid, maybe the sulphide layer as some
lanthanide sulphates are not that soluble, especially not in strong sulphuric acid. I removed the lump, washed and dried it and checked the weight and
it was still close to 43g.
I then reacted the lump with 33% hydrochloric acid. This time the vigorous reaction persisted, and pink-ish solution quickly formed. By my
stoichiometry app 81g of 33% HCl would be needed to dissolve the 43g erbium, I added 20g of HCl every so often to keep the reaction going nicely and
then left it going for the night. I also added a bit of water when it got too vigorous.
The next morning there was no sign of any reaction and very little acid smell and I filtered the solution. There was still a 0.8g piece of what
appeared to be erbium and around half a gram of black sludge, I assume there was some impurities in the lump of metal.
I ended up with 180g solution, the ErCl3 that formed should have been around 65g, so I would proceed on the basis that 28g of solution contained 10g
ErCl3 anhydrous to make various erbium compounds.
I also realised my ErCl3 won’t be enough for all the things I wanted to try so I reacted some of the oxide Er2O3 with strong sulphuric acid to make
25g Er2(SO4)3. As usual a volume of a few 100ml water had to be used to dissolve all the sulphate, the solution was then boiled down to 50ml and the
precipitated erbium sulfate filtered off while near boiling, washed with boiling water, and dried under a metal dish in the sun. The dry yield was 20g
of hydrated glistering pink powder. I must still work out why the yield was lower than I usually expect when I make lanthanide sulphates in this way.
I was now ready to try and make different erbium compounds.
I also attached one family photo. The photo do not quite do the colours justice, the salts do look subtly different which don’t always show up on
the photo.
Edit: fixed typo in title
[Edited on 5-15-2020 by Texium (zts16)]
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Lion850
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*** Part 2 ***
Erbium Chloride ErCl3:
28g of the solution made earlier (thus corresponding to 10g anhydrous ErCl3) was placed in a desiccator under vacuum over NaOH. When checked 2 days
later most of the water had gone but it was still a wet paste, pinkish in colour.
I then put it in my sand bath, with sand temperature around 180C. It melted and boiled very gently for a short time before recrystalizing. The moment
the last water disappeared I removed the crucible from the sand bath the agitated the pink contents while it cooled. I ended up with dry, rock hard
little pieces with a pink colour. Total weight was 12.5g, more than the 10 that in theory was in the solution but of course the final product is a
hydrate. I was quite pleased that it dried in air without any significate change to the colour, plus it dried quick so I think most remained ErCl3
(and did not react with the oxygen in the air to make the oxy-chloride). See photo in original post above.
Erbium Fluoride ErF3:
33g of my ErCl3 solution (which should be 12g ErCl3) was mixed slowly with a solution of 6g NH4F (slight excess) dissolved in 15ml water.
ErCl3 + 3NH4F = ErF3 + 3NH4Cl
A pale pink suspension formed. Water was added to increase the solution to 100ml total so it could be stirred. After 20 minutes stirring it was
filtered and was washed twice with cold water in the funnel. The clear filtrate was discarded, and the pink remainder dried overnight in a desiccator.
Unfortunately the 2 halves of the desiccator were stuck the next morning, after the pressure was equalized, and when I tried to get it to slide open
it got shocked causing some of the dry ErF3 into the NaOH below. So while I could still recover 6.2g of dry ErF3, I will never know what my yield was.
See photo in original post above.
Erbium Chromate Er2(CrO4)3:
I was interested to see what colour erbium chromate or dichromate would be. Hoping for a salt that was not pink! I could not find much info online.
The initial plan was to react solutions of potassium dichromate and erbium chloride and get a double displacement with insoluble erbium dichromate or
chromate:
2ErCl3 + 3K2Cr2O7 = Er2(Cr2O7)3 + 6KCl
14.5g of potassium dichromate was dissolved in 150ml warm water (took a while to dissolve). 10g of ErCl3 in solution was then added under stirring.
Nothing happened, it just looked like the potassium dichromate solution. I left it overnight, but it was the same the next morning; no obvious sign of
a reaction; no colour change or ppt.
I decided to give up on this, but I did not want to lose the erbium. So I decided to add 10g NaOH to ppt out erbium hydroxide which could then be
filtered out. Much to my surprise I got a beaker full of yellow suspension when the NaOH was added. I suspected that adding NaOH caused erbium
chromate to form, or possible a double salt.
To test this further, I dissolved 2 grams of potassium dichromate in a small amount of water and dissolved 2g of sodium hydroxide in water and mixed
the solution. The solution went from orange to yellow, and I learned online that the potassium dichromate and sodium hydroxide reacted giving sodium
chromate in solution which is yellow:
K2Cr2O7 + 4NaOH → 2Na2CrO4 + 2KOH + H2O
I then dripped a few drops of erbium chloride solution into this yellow solution, and immediately each drop of erbium chloride formed a yellow
suspension that settled out. So I assume the erbium chloride reacted with the sodium chromate:
2ErCl3 + 3Na2CrO4 = Er2(CrO4)3 + 6NaCl
I then filtered the yellow product out of the original solution and washed it 3 times with water in the filter. Even after the 3rd wash the water
running through was very pale yellow but I then saw somewhere online erbium chromate is “somewhat soluble”.
The wet yellow paste was 61g, and it took many hours on the steam bath over a few days until the dry weight reached 9.8g and then did not reduce any
further. I wondered if any KOH remained with the product; I left it out overnight to see if the weight increases – if it absorbs moisture – but it
did not and still appeared bone dry the next morning. If what I got was only erbium chromate and nothing else, the yield was around 78%. It’s a nice
yellow colour dried. See photo in the original post above.
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Lion850
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** Part 3 **
Erbium Bromide ErBr3:
Er2(SO4)3 + 3CaBr2 = 2ErBr3 + 3CaSO4
11g erbium sulphate was dissolved in water, it was a struggle to get all dissolved in a clear solution and eventually this was achieved with 300ml
solution volume. 12g calcium bromide was dissolved in 15ml water. This should have been a slight excess of CaBr2 as the CaBr2 hydration is not known.
It was added to the erbium sulphate solution under stirring. The displacement reaction took its time, the solution slowly became cloudy and the white
of calcium sulphate started to be seen. The solution was left to stir overnight.
The next morning once stirring was stopped a white ppt quickly settled. The solution was filtered giving a clear pink 300ml solution and white
remainder. The pink solution was boiled down to around 50ml and then placed in the desiccator.
After 2 days the ErBr3 was a wet jelly. I wanted to dry it further in the sand bath but my hotplate failed! So it was transferred to the vial wet,
19g. The colour of the wet salt is a bit darker than most of the others, there is a hint of red in the pink. See photo in the original post above. It
will be re-dissolved and dried at opportune time in future.
Erbium Acetate Er(CH3COO)3:
First attempt was to react some glacial acetic acid direct with erbium oxide, but there seemed to be no reaction. 10g of oxide was then reacted with
25g 33% HCl to give 14g ErCl3 in solution (I had used all the ErCl solution I made earlier).
Er2O3 + 6HCl = 2ErCl3 + 3H2O
The solution was increased to 60ml by adding water and then boiled down to 20ml, to drive off excess hydrochloric acid. The solution of erbium
chloride was then reacted with 15g potassium carbonate dissolved in 30ml water.
2ErCl3 + 3K2CO3 = Er2(CO3)3 + 6KCl
This gave a mass of pink ppt, this was vacuum filtered and then extensively washed with water in the filter. A small piece of this wet pink remainder
was tested with HCl, and bubbled nicely as a carbonate should.
12g glacial acetic acid and 20ml water was poured into a beaker, and pieces of erbium carbonate added with continual stirring. The carbonate dissolved
into solution with bubbling, not as fast as with a stronger acid but it proceeded slowly. This was left stirring overnight.
8Er2(CO3)3 + 27CH3COOH = 8Er2(CH3COO)3 + 30CO2 + 18H2O
The next morning the reaction seemed complete, with pink ppt. The solution was then topped up to 120ml to check if all the ppt can dissolve – it
dissolved very easily showing that it was not leftover carbonate. The solution was boiled down to around 50ml to drive off excess acid, by this time
it was also starting to crystalize. It was placed in a crucible in the desiccator.
After 24hrs the crystals were bone dry. Of all the erbium salts this is, to me, the most appealing pink: a very ‘soft’ appearance. Yield was 18.1g
which was a bit more than expected: it can be explained if it is an octahydrate .8H2O but online I can only find a tetrahydrate .4H2O mentioned. So
either there is still some moisture even though it seems completely dry or I messed up somewhere and started with a bit more than 10g oxide.
The final product has a slight vinegar smell. See photo in the original post above.
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Lion850
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** Part 4 - last part **
Erbium Sulphide Er2S3:
The plan was to react 10g erbium chloride in solution with 7g sodium polysulphide in solution, but I knew from past experience to expect anything when
trying sulphide double displacement in water:
2ErCl3 + 3Na2S = Er2S3 + 6NaCl
The erbium chloride solution was slowly added to the sodium sulphide solution. Each time a bit was added there was a reaction with bubbles, H2S could
be smelled strongly, and a light grey suspension formed. After all was added and some stirring time the reaction seemed to be complete and it was
filtered. The filtrate was a light green, similar to the original sodium sulphide solution just more pale. The filtrate smelled of H2S and was
discarded.
The remainder was not rinsed in the funnel to avoid getting it in contact with water in which there is no H2S present. The remainder smelled of H2S
and was left outside under a cover for the night. Wet it was a greyish color with a hint of olive green. The next morning it had started turning pink!
And the H2S smell was a lot less. It was placed in a steam bath; the initial wet weight was 43g.
As it dried the colour became steadily more pink. After many drying runs the final weight remained unchanged at 11.7g. It appeared very dry with no
more H2S smell. Colour a bit darker pink than the other salts, see photo in original post above.
But what is it? I tried reacting small pieces with hydrochloric and nitric acid expecting, if it is a sulphide, to see bubbles and smell H2S but this
did not happen. With concentrated sulphuric acid there seems to be some bubbles and it then formed a pink solution. The bubbles do not smell of H2S,
or anything else for that matter, although I tried only a tiny piece. I thought I may have somehow ended up back at the chloride, but it also seems
insoluble in water which rules out being the chloride.
Any ideas?
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woelen
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Very nice set of experiments. Good work!
The last one (the sulfide experiment) is actually quite boring. What you made is erbium hydroxide (or mixed hydroxide/oxide).
Sulfide ion is a VERY strong base, stronger than hydroxide. In water, the sulfide ion can hardly exist. It reacts with water:
S(2-) + H2O --> HS(-) + OH(-)
This reaction is nearly complete, in water, you will not see any noticeable amount of S(2-) ion.
The HS(-) still is quite basic and in water it reacts as follows:
HS(-) + H2O <---> H2S + OH(-)
The latter reaction is an equilibrium. You can smell H2S, but there also still is quite some HS(-).
Your erbium precipitates with the OH(-) ions, giving Er(OH)3. Hardly any sulfide will be present in your precipitate. This also explains why you do
not get any bubbles nor any smell from the pink solid on addition to acid, which you asumed to be the sulfide.
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j_sum1
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Nice experiments Lion850.
Well worth the time to read through.
I know nearly nothing about lanthanides but they have always fascinated: mostly because no one mentions them much. I wish Brain and Force was still
around.
Really cool to have a family photo like that. Hopefully I will get a chance to see them in person one day: if the world ever returns to normal.
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Bedlasky
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Nice preparations.
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Lion850
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Thanks for the comments gents and also thanks Woelen for the explanation regarding the sulphide.
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DraconicAcid
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Very nice!
I'm bumping this because I made some very nice little crystals of erbium(III) sulphate octahydrate by slow evaporation of water from a solution
containing excess sulphuric acid.
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.
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