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alexleyenda
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Quote: Originally posted by bismuthate  | | Could the colourless stage somehow be potassium chromite? I have no idea how it could have formed but it would explain the clear colour.
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Well at first does potassium chromite even exist?? When I search for it I get no result.
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bismuthate
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Well sodium chromite exists so I'll bet that potassium chromite does too.
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Zyklon-A
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Does anyone know what reaction Dr. Steve Liddle is talking about in The Favorite Reactions video, by Periodic Table of videos? (1 minute, 45 seconds in)
He talks about reacting P4 with Na-K alloy and then adding another reactant (of who's name he doesn't disclose).
He says its an extremely dangerous procedure (as evidenced by the description above.)
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PHILOU Zrealone
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| Quote: Originally posted by Zyklon-A | Does anyone know what reaction Dr. Steve Liddle is talking about in The Favorite Reactions video, by Periodic Table of videos? (1 minute, 45 seconds in)
He talks about reacting P4 with Na-K alloy and then adding another reactant (of who's name he doesn't disclose).
He says its an extremely dangerous procedure (as evidenced by the description above.)
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Maybe the following?
3 Na + P --> Na3P(s)
3 K + P --> K3P(s)
Na3P(s) + 3 H2O(l) --> 3 NaOH(s) + PH3(g)
K3P(s) + 3 H2O(l) --> 3 KOH(s) + PH3(g)
2 PH3(g) +3 O2(g) --> P2O3(s) + 3 H2O(l) --> 2 H3PO3 (l)
phosphine
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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papaya
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Can I use sodium carbonate as a standard for acid titrations ? The indicator used will be methyl orange, but I didn't hear that Na2CO3 is ever used
as a standard, why? It has the advantage that it can be prepared completely free of water, it's fairly soluble, more stable to atmospheric conditions
than NaOH etc.. I prepared it from sodium bicarbonate by heating the baking soda powder to 600C in the course of 1 hour, the mass change was from
initial 19g of NaHCO3 to 11.9g, which is exactly what the theory predicts it should be when completely turned into carbonate. is there some serious
drawback it can't be used for acid titrations ?
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Metacelsus
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No, it's fine (better than NaOH, IMO).
(Assuming you're titrating a reasonably strong acid, that is.) Carbonate isn't as strong a base as hydroxide.
[Edited on 6-7-2014 by Cheddite Cheese]
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papaya
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Yes cheddite, I need it for strong acids and if it works then some other related questions: which indicator is better in that case methyl orange(I
think) or phenolph
thalein ? also I cannot figure out what concentrations I have to prepare both the titrant and titrand? Assuming I know very approximately that for
example my sulfuric acid is 5M then I can initially take equal volume of 5mol/L Na2CO3 or 2x volume of 2.5mol/L or, or...
, or I could dilute both sides beforehand.. but why?
I just don't know which is more accurate and how to adjust concentrations for best results (how the precision is dependent on initial concentrations?)
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Metacelsus
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Use a relatively dilute solution of sodium carbonate (solubility 2.02 M at 25 C, your solution should be below 1 M) so that you can more accurately
dispense a given amount and not have to deal with tiny volumes.
Phenolphthalein is a good indicator.
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papaya
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Thank you, I thought phenolphthalein is worse in this case because it's color transition occurs under basic pH 8.3–10.0 according to wiki and since
carbonate is not a strong base this may be further from neutralization point compared with methylorange. But I agree, I also like it.
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Metacelsus
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I use it because it's easy(ish) to get. I assume the change occurs at pH 9 and adjust my calculations accordingly.
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papaya
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Hmm, interestingly I found here that phenolphtalein is not suitable for acid standardizations with carbonate, since it'll change color already on
half neutralization
http://www.monzir-pal.net/Lab%20Manuals/Practical%20Quantita...
Other question: if I use methyl orange (full neutralization) which solution must be in the burete and which in the beaker ?
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Metacelsus
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If you account for the bicarbonate/carbonate equilibrium, it is possible to use phenolphthalein.
The acid solution with indicator should be in the beaker, and the carbonate solution should be in the burette.
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papaya
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Just read the page I provided
"however, in precence of phenolphthalein indicator, the end point of the reaction between Na2CO3 and HCl appears when the reaction proceeds to the
point of NaHCO3 formation which requires half the volume of HCl consumed in the previous example.
Na2C03 + HCl = NaCl + NaHC03
The molarity of HCl in the previous example can be calculated by substitution of a 1:1 mole ratio of HCl to Na2CO3."
Thus, when titrating carbonate with acid (in burette) phenolphtalein color will fade when all carbonate is turned to bicarbonate - that's half way to
neutralization.
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papaya
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I performed titration of most concentrated H2SO4 I could find( diluted by 1:50 ) with Na2CO3 solution,indicator is methyl orange( actually I titrated
Na2CO3 with H2SO4, since the last was in the burette) which gave molarity of 18.3M (correspondents to 97% H2SO4). However I'm quite sure my sulfuric
is not more than 90% conc - density is below 1.8 if I remember correctly from last measurement. This may indicate that carbonate is somewhat
inconvenient for titrations, however what else can be used ?(I mean when no primary standards are commercially available) What about borax, is it
better than carbonate?
I think determination of the concentrations of technical products available to amateur chemists is an important matter, however I don't see threads
discussing this - what are most viable and accurate ways of estimation of acid strenghts, what standarts do You use?
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arkoma
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I salted out, then distilled isopropyl alcohol. Can I dry it further with lithium metal? Or will I be getting a visit from the fire department?
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Brain&Force
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Lithium reacts to form lithium isopropoxide in isopropanol, so you'll just be contaminating it more. Not explosively AFAIK, but don't risk it.
At the end of the day, simulating atoms doesn't beat working with the real things...
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Metacelsus
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You can dry it further by distilling a mixture of it and calcium oxide (quicklime). (I know this works for ethanol, and it should work for
isopropanol).
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AlphaDecay
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I want to convert Calcium carbonate into a soluble calcium salt, but without the use of any acid. Is that possilble? Any suggestions?
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Metacelsus
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It's possible, but not worth it in my opinion.
1) Heat it strongly to decompose it to CaO.
2) Dissolve in water (Ca(OH)2 is weakly soluble).
3) Precipitate with a water-soluble salt whose cation forms an insoluble hydroxide, and then filter. You'll end up with a solution of calcium ions and
the anion you want.
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AlphaDecay
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Well, I do not have the required equipment to calcinate it. But I can try with the Calcium hydroxide instead. Thanks for suggestions.
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Texium
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Alright, I have a quick question. Is it ok to put a round bottom flask directly onto a hot plate if it isn't a coil type one? I've seen it done in
many pictures on here before, but I have also read before that it's not a good thing to do.
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gdflp
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A rbf sitting directly on a hot plate will not be as effective as using a heating mantle or some other method of heating which has more surface area
than the round bottom flask, but there is no reason you can't. To attain faster heat transfer an air bath, made by trapping air between the hot plate
and the flask with a cloth or aluminum foil or such, or an oil or water bath will heat the flasks up much quicker and give you a better idea of what
temperature the flask is at.
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Texium
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Alright cool, thanks, I'll use the air bath then.
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arkoma
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| Quote: Originally posted by zts16 | | Alright, I have a quick question. Is it ok to put a round bottom flask directly onto a hot plate if it isn't a coil type one? I've seen it done in
many pictures on here before, but I have also read before that it's not a good thing to do. |
I put my chinese one directly on the hotplate, and the bottom fell out. deschem warrantied it, but I'll not try putting it directly on the element
again
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Texium
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Is your hotplate of the type that has the direct metal coil? If so, that's probably why.
Also, what about a Florence Flask? That could be heated directly on a hotplate with ceramic wire gauze, right?
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