| Pages:
1
2
3
4 |
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
7 mol/L means 7 mol/L x 162.2 g/mol = 1135.4 g FeCl3 / L.
Now we assume that when FeCl3 and water are mixed no contraction or expansion takes place. This is certainly true for dilute solutions (< 1 M).
That one litre is made up of 1135.4 g / 2.898 g/cm<sup>3</sup> = 392 cm<sup>3</sup> (or ml, if you prefer) of FeCl3. The rest
of that 1 L is made up of water, i.e. 1000 - 392 = 608 ml.
Since as the density of water is 1, 608 ml of water = 608 g of water.
So we have (1135 g FeCl3 + 608 g water) / (392 ml FeCl3 + 608 ml water) = 1.74 g/ml (g/cm<sup>3</sup>
[Edited on 28-5-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
I throw my hands in the air. I throw my hands in the air.
I did not mean to the above, I meant to Draconic's revelation about the molarity with a 1.32 density and a 2.59 M
[Edited on 28-5-2014 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Yes, that one's a bit tricky when one is not math minded.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
No, but the good news is that I am just intelligent enough to reverse engineer everything I come across. So I always see an example and an answer
then I take things apart to see how it is done and then that's it. So I understand all the reasoning now. I just can't reason maths out from scratch
- a weakness of mine.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
That kind of tallies: I get 1.16 g/ml for 1.5 M.
[Edited on 28-5-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
all this wonderful bad news means that my titration must be wrong, or there is ferrous still in the solution. Anyway we will see.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
I will test the sample for ferrous ions, so we'll know. It's highly unlikely though...
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
On Chris’ sample, for density relative to water, I got 1.36, which isn’t too far from Chris’ own value.
But here’s a surprise; when testing for ferrous iron:
Left: 2 drops of the ferric solution with about 1 mm of water.
Middle: same as left but with 0.5 ml of K3Fe(CN)6 reagent solution added.
Right: same as left but with a few grains of FeSO4 added and with 0.5 ml of K3Fe(CN)6 reagent solution added.
Middle and left show strong formation of Prussian Blue (Fe<sub>7</sub>(CN)<sub>18</sub>, idealised) due to presence of
Fe<sup>2+</sup>. So the ferric chloride solution still contains ferrous ions, but this test cannot tell me how much.
Tomorrow the Fe<sup>3+</sup> will be titrated.
[Edited on 6-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Absolutely great news, about my measurements, was dreading the moment you tested it to be honest thinking he's bound to find my horrendous
embarrassing mistake. That there are still ferrous ions in solution is a surprise, yet paradoxically also good news since my 0.5 mol iron can not
simply vanish. This gives me new insight into length of time needed without pumping air, without peroxide, to obtain ferric from ferrous. It has been
3 weeks at least now.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
It did surprise me a little to find such a strong positive for Fe<sup>2+</sup>. It's a shame so little of the original solution is left,
otherwise I might try and complete the oxidation for a second titration. Let me think about that...
Loss of peroxide during the oxidation may be partly responsible here. The reduction of the peroxide is supposed to go according:
H2O2 + 2 H+ 2 e- === 2 H2O
.. but often oxygen effervescence can be observed during oxidations with peroxide:
H2O2 === > O2 + 2 H+ + 2 e-
This side reaction is OXIDATION of H2O2 to oxygen and doesn't contribute anything to the oxidation of Fe2+ to Fe3+. So too much effervescence may
leave one short of the desired stoichiometry.
[Edited on 6-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by blogfast25  | It did surprise me a little to find such a strong positive for Fe<sup>2+</sup>. It's a shame so little of the original solution is left,
otherwise I might try and complete the oxidation for a second titration. Let me think about that...
Loss of peroxide during the oxidation may be partly responsible here. The reduction of the peroxide is supposed to go according:
H2O2 + 2 H+ 2 e- === 2 H2O
.. but often oxygen effervescence can be observed during oxidations with peroxide:
H2O2 === > O2 + 2 H+ + 2 e-
This side reaction is OXIDATION of H2O2 to oxygen and doesn't contribute anything to the oxidation of Fe2+ to Fe3+. So too much effervescence may
leave one short of the desired stoichiometry.
[Edited on 6-6-2014 by blogfast25] |
Hi, I'm trying to interpret, did you add peroxide to the solution before the prussian blue precipitate in order to ensure complete oxidation?
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by CHRIS25 | | Hi, I'm trying to interpret, did you add peroxide to the solution before the prussian blue precipitate in order to ensure complete oxidation?
|
No, no, not at all. The test was conducted on the sample as I received it (diluted 2 drops to 1 ml water). It clearly contains ferrous ions. The third
tube is simply a reference test.
Had I completed the oxidation by adding peroxide I wouldn't have found any Prussian Blue. Which I hope to demonstrate later on today.
I was trying to provide an explanation for why your ferric chloride still contained ferrous chloride: possibly some of the peroxide you used got
consumed into this side reaction.
[Edited on 7-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
I feared that: I never use peroxide ever for oxidizing as a short cut. This sample has been oxidized by natural exposure to air over nearly 4 weeks
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by CHRIS25 | | I feared that: I never use peroxide ever for oxidizing as a short cut. This sample has been oxidized by natural exposure to air over nearly 4 weeks
|
So was that the only oxidising action? Because that would explain a thing or two: air (oxygen) oxidation of Fe<sup>2+</sup> in strongly
acidic conditions at RT is notoriously slow, despite what many of the usual suspects say.
[Edited on 7-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
On sunny days it went outside with the covering off. But I knew it was slow, just not this slow.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Ok, mystery finally solved: your ‘ferric chloride solution’ is mainly ferrous chloride.
Here’s what I did.
1) 2.0 ml of the original sample (OS) was pipetted into a 100.0 ml volumetric flask, then diluted to the mark (dilution factor 100/2=50). Call this
solution 1.
2) Another 2.0 ml of the original sample (OS) was pipetted into a small conical flask, slightly diluted and put in the fridge. Call this solution 2.
3) Solution 1 was titrated with KI and 0.1 N Na2S2O3. The end points were very variable. I suspect some of the Fe<sup>2+</sup> is
oxidising (then oxidises more iodide) during the titration. Very tentatively I got a value of 1.4 M for Fe<sup>3+</sup>
4) To Solution 2 was added about 10 ml H2O2 32 %, very slowly, almost drop by drop. The solution changed colour quite dramatically and much heat
evolved, all signs of ferrous ions being oxidised by the peroxide.
5) To get rid of the excess peroxide (which would also oxidise iodide, thus creating false readings) the oxidised solution 2 was boiled for about ½
hour. This caused predictably the Fe<sup>3+</sup> to precipitate as Fe(OH)3. After cooling 10 ml 98 % H2SO4 was added, which dissolved the
Fe(OH)3 immediately.
6) This oxidised solution 2 tested negative for Fe<sup>2+</sup> with K3Fe(CN)6.
Here solution 2 (left) after oxidation, compared to solution 1 (right). It’s much more coloured:
7) Solution 2 was quantitatively transferred into a 100.0 ml volumetric flask and diluted to the mark (dilution factor 50), then titrated as above. I
found what is now TOTAL Fe (titrated as Fe<sup>3+</sup> to be 3.9 M.
8) Another quick test showed that when the OS is slightly diluted and then precipitated with strong ammonia, black magnetite formed
(Fe<sub>3</sub>O<sub>3</sub>, the mixed oxidation state oxide). This is typical of solutions that contain ferrous and ferric
ions both in significant quantities.
So roughly over half of the iron had not been oxidised from the ferrous to the ferric form. Considering what a poor oxidiser air
oxygen is in acid conditions (for this oxidation), this is hardly a big surprise.
[Edited on 7-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Well then, thanks to all your hard work Gert, a lot learned, a lot solved, and more techniques learned through this process. I have K ferricyanide
and did not use it to test for ferrous ions because I was always led to believe, during my darkroom days, that this stuff should never come into
contact with acids of any sort - so is it really safe to use below a certain acidity strength?
The production of magnetite is a dead give away. But I am so surprised that half the solution was still in the ferrous stage. I think now I will get
out the air pump and pump away, (I only have 5% peroxide and it is ridulous adding so much water just to oxidize); so air pump from now on.
In your point 7, you say 3.9 M. But this does not tell me how many moles ferric in the solution. If I take my 50 mLs (from which the sample was
taken) then this is only 0.195 moles ?????
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Ferro and ferrihexacyanates are very safe, even ay low pH. One of the two is even used as a food additive!
These substances are very strong complexes, so that the CN groups linked to the central Fe atom are bonded very, very, strongly to it.
To get HCN evolution you'd need strong acid + heating. Don't confuse complex cyanides with simple cyanides like NaCN or KCN: these simple cyanides
evolve HCN just by showing them the acid bottle! But that's not the case here...
3.9 M applies to all of the solution you had. I seem to remember 70 ml. So that would be 3.9 M x 0.07 L = 0.273 mol. I know, that's a lot of Fe lost
but I'll bet you your next attempt will be much better. But you will need some oxidiser, other than air oxygen. Have you any nitric acid?
[Edited on 7-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Yes, but I am going to use my air pump, I use it for copper chloride, not in the mood for complicating stuff right now, too many things not going
according to expectations, annoyance levels higher than usual; frustration barometer has just entered orange, and "throw whole lot in bin" emergency
release valve has just entered critical.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
My only attempt ever to oxidise a ferrous salt (sulphate in this case) to Fe(III) using an air pump failed. Sadly I predict the same will happen
here...
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Really? I always use an air pump with HCl and Cu, never had any issues. So what are you suggestions then?
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
Gently heat 3% OTC peroxide for ages to get a slightly stronger H2O2 solution.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Ages ago I watched a chemist (Video) put peroxide in the freezer of a lab, and then dripped out a few of the first drops that melted saying that this
was Highly concentrated. That is all I remember.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by CHRIS25 | | Really? I always use an air pump with HCl and Cu, never had any issues. So what are you suggestions then? |
It seems I lost a post here, for some reason.
Don't compare apples and oranges: what works for Cu + HCl doesn't necessarily work for this system.
If you have nitric acid, use that to oxidise the ferrous iron to ferric iron. You need 1/3 (one third) of a mol of nitric acid per mol of ferrous
iron.
That reaction n requires some care to carry it out properly and safely though.
Another way of preparing FeCl3, without special oxidisers, is as follows. Start from a known quantity of ferrous sulphate heptahydrate or ferrous
chloride. Precipitate with ammonia as Fe(OH)2, filter and wash filter cake with plenty water. The filtrate will contain ammonium sulphate or ammonium
chloride, which can be recovered.
Place all of the filter cake in a borosil container and heat gently on a hot plate, always making sure the material remains moist (add small amounts
of water to prevent it from drying out). The Fe(OH)2 will oxidise quite quickly to Fe(OH)3 by air oxygen, simplified:
4 Fe(OH)2 + O2 + 2 H2O ===> 4 Fe(OH)3
The material will change to reddish brown. This oxidation reaction is much faster than FeCl2 in acid solution, like you've been trying.
Then dissolve the Fe(OH)3 in excess hot HCl 37 %
[Edited on 8-6-2014 by blogfast25]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
After some thought I decided that I need to test this out. I will (given the weather) pump oxygen into the solution for as long as is possible,
noting times and amounts. Then re-do titration and ferricyanide tests, let's see how much oxidizes, since we now know how much is already oxidized.
Curious.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
| Pages:
1
2
3
4 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
