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blogfast25
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Quote: Originally posted by Ramium  | is it possible that i added to much HCL so when the copper phosphate formed it was dissolved by the HCL forming a solution
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Yes but it doesn't matter: as Tear's experiment and my calcs show H3PO4 will not precipitate copper phosphate from CuCl2 solutions.
For future efforts you will need to keep tight control of the amount of HCl used to dissolve the copper basic carbonate. If you 'overshoot' and the
resulting solution is acidic then you need to neutralise the excess HCl with NaOH.
You will need to neutralise some of your 5.1 M H3PO4 with NaOH solution to get a Na3PO4 solution.
H3PO4 + 3 NaOH === > Na3PO4 + 3 H2O
[Edited on 3-2-2015 by blogfast25]
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Amos
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Rather than use NaOH, you can also add simple baking soda(sodium bicarbonate) to a solution of your phosphoric acid until the fizzing stops and then
add a small amount of additional phosphoric acid to destroy excess base. Be sure not to add the sodium bicarbonate too fast, as the reaction bubbles a
lot and can easily cause the solution to overflow.
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Zombie
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Yes Ramium. Your Copper Phosphate is still in solution, and needs a base to precipitate it.
I have to give you a LOT of credit for your age. You managed to hang w/ the big dogs. All the while keeping track on your project.
Good work.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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blogfast25
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| Quote: Originally posted by No Tears Only Dreams Now | | Rather than use NaOH, you can also add simple baking soda(sodium bicarbonate) to a solution of your phosphoric acid until the fizzing stops and then
add a small amount of additional phosphoric acid to destroy excess base. Be sure not to add the sodium bicarbonate too fast, as the reaction bubbles a
lot and can easily cause the solution to overflow. |
Yes, that would work.
Did you remove that link to 'wikia' on copper phosphate? If so can you post it again? I'd like to comment there that CuCO<sub>3</sub>
simply doesn't exist.
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Shivachemist
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Yeah Zombie is right. It precipitates only under alkaline conditions or at least the salt you using for precipitation must be neutral and we can use
any basic phosphate (trisodium phosphate) to precipitate it from the metallic salt. Does anyone have basic salt like Magnesium or Calcium acetate? or
even we can use trisodium phosphate for precipitation as it is alkaline in nature. Just wanted to show how it works. But I have only monosodium
phosphate which is almost neutral to slightly acidic.
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Ramium
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So if i add a small amount of sodium bicarbonate to my solution copper phosphate will pricipitate???
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Ramium
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Also my solution has turned greener is that bad???
[Edited on 4-2-2015 by Ramium]
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Zombie
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It's simply continuing the reaction. It's actually a good thing.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Shivachemist
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Yep, but I would recommend you to use trisodium phosphate to precipitate phosphates as it is strongly alkaline in nature and cheap as well (cheaper
than phosphoric acid).
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Amos
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| Quote: Originally posted by blogfast25 |
Did you remove that link to 'wikia' on copper phosphate? If so can you post it again? I'd like to comment there that CuCO<sub>3</sub>
simply doesn't exist. |
I don't think I did, but here it is again: http://sciencemadness.wikia.com/wiki/Copper%28II%29_phosphat...
You've got me curious now, when did copper(II) carbonate stop existing? The wikipedia article appears to have changed quite recently, and there's also
now a wikipedia article on copper(II) phosphate that seems to disagree with most of the work I've done with the compound.
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blogfast25
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| Quote: Originally posted by Ramium | So if i add a small amount of sodium bicarbonate to my solution copper phosphate will pricipitate???
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No. The amount of sodium bicarbonate needs to be at least equivalent to the amount of phosphoric acid you originally added:
H3PO4 + 3 NaHCO3 === > Na3PO4 + 3 CO2 + 3 H2O
Just keep adding NaHCO3 slowly until fizzing stops and precipitation starts.
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Metacelsus
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Will that reaction go all the way to trisodium phosphate, or will it stop at the disodium salt? Sodium bicarbonate isn't very basic, and the pKa of
disodium phosphate is 12.38, according to Wikipedia. You might need to use sodium hydroxide for the last deprotonation.
(Sorry, didn't read the full post. You might not need to deprotonate it all the way, as the copper phosphate will nonetheless precipitate.)
[Edited on 4-2-2015 by Cheddite Cheese]
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blogfast25
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| Quote: Originally posted by Cheddite Cheese | Will that reaction go all the way to trisodium phosphate, or will it stop at the disodium salt? Sodium bicarbonate isn't very basic, and the pKa of
disodium phosphate is 12.38, according to Wikipedia. You might need to use sodium hydroxide for the last deprotonation.
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A small excess of NaHCO3 will create the pH in which phosphate ions can exist and you don't need much of it to exceed the solubility limit of copper
carbonate!
Ks = [Cu]<sup>3</sup>[PO4]<sup>2</sup> = 1.4 x 10<sup>-37 </sup>
For [Cu] = 1 M, [PO4] = (1.4 x 10<sup>-37</sup> <sup>0.5</sup> = 3.7 x 10<sup>-19</sup> or pPO4 = - log[PO4] = 18.4
Also:
[H3O]<sup>3</sup> [PO4]/[H3PO4] = K1 K2 K3
Assume [H3PO4] = 1 M and take - log of both sides:
3 pH + pPO4 = pK1 + pK2 + pK3
3 pH + 18.4 = 21.7 = > pH = 1.65
So even a quite partial neutralisation of the phosphoric acid will cause copper phosphate to <i>start</i> precipitating.
[Edited on 4-2-2015 by blogfast25]
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Shivachemist
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Well, carbonates and bicarbonates are usually used to prepare Disodium hydrogen phosphate.
H3PO4 + 2 NaHCO3 ------> Na2HPO4 + 2 CO2 + 2 H2O
Then the solution should be warmed gently to expel excess of CO2 present in the solution. Disodium hydrogen phosphate is feebly basic in nature. So,
it may not precipitate phosphate if the salt solution is moderately or very acidic. But, It will work for neutral salts or feebly acidic salts I
believe.
However, trisodium phosphate can be obtained just by treating the aqueous solution of Disodium hydrogen phosphate with calculated quantity of Sodium
hydroxide solution.
Na2HPO4 + NaOH -----> Na3PO4 + H2O
The anhydrous form can be prepared by fusing it up with Sodium carbonate:
2 Na2HPO4 + Na2CO3 -----> 2 Na3PO4 + H2O + CO2
[Edited on 4-2-2015 by Shivachemist]
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blogfast25
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| Quote: Originally posted by Shivachemist | Well, carbonates and bicarbonates are usually used to prepare Disodium hydrogen phosphate.
H3PO4 + 2 NaHCO3 ------> Na2HPO4 + 2 CO2 + 2 H2O
Then the solution should be warmed gently to expel excess of CO2 present in the solution. |
Nah, just use NaOH:
H3PO4 + 2 NaOH === > Na2HPO4 + 2 H2O
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Shivachemist
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That is possible too. There is always more than one route to prepare a compound.
[Edited on 4-2-2015 by Shivachemist]
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Amos
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The sodium phosphate(not precisely sure which salt) I produced to make my copper phosphate only used baking soda and phosphoric acid, and an excess of
this salt was sufficient to completely convert the copper sulfate I used.
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blogfast25
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Thanks for the wikia link, NTODN.
It does indeed not matter much which type of soluble orthophosphate is used, as long as the solubility product of copper phosphate is exceeded when
mixing the solutions.
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Ramium
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So my understanding is if i add sodium bicarbonate very slowly to the solution untill the fizzing stops
The copper phosphate should pricipitate is that correct???
[Edited on 4-2-2015 by Ramium]
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gdflp
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Yes, dissolving the bicarbonate in water first might help make it easier to control the amount you are adding. By adding the basic bicarbonate,
you're increasing the pH and consequently increasing the number of free phosphate ions in solution. I apologize, I completely forgot in my first post
that phosphoric acid doesn't dissociate much.
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blogfast25
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Actually, with a pK<sub>a1</sub> of 2.15 (Wiki) phosphoric acid is a fairly strong acid but subsequent deprotonations are quasi
non-existent in pure H3PO4 solutions.
[Edited on 4-2-2015 by blogfast25]
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gdflp
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I meant that it doesn't dissociate much into PO43- ions, there are quite a bit of H+ and H2PO4- ions as
you said based on the pKa1.
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Ramium
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I just added the sodium bicarbonate it bubbled up very high(3 times the volume of the origanil solution)the foam has bits of blue in it i think thats
the copper phosphate so i will let the sun debubble it then filter to get the copper phosphate
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blogfast25
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Try and filter it off, wash and dry properly and determine yield.
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Ramium
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Yes yes yes yes yes!!! It worked i got heaps thank you all so much i love you all
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