Kh2po4 Components?

[Schmill]

I've found the following information at this website:

[URL="http/www.csd.net/~cgadd/aqua/art_plant_dosage_calc.htm"]http/www.csd.net/~cgadd/aqua/art_plant_dosage_calc.htm[/URL]

KH2PO4
- PO4 - Phosphate 69.8%
- KH2 30.2%

So now I know that when I dose some KH2PO4, 69.8% of it is Phosphate, and 30.2% is 'something else'.

I'm guessing it's K (potassium), H2 (2 parts hydrogen), but I can't work out what of the 30.2% is what.
I can see that it's 1 part K, 2 parts H, but I don't think it's as simple as saying 1/3 of it is potassium?

Anyone able to help please?



Thanks

 

[backtotropical]

It's probably worth posting this in the 'Planted Tank' section mate. You may get a better response.

 

[Schmill]

Cheers, got something similar there and was pretty much told it didn't matter, but now it's a 'scientifically curious' question

 

[Bignose]

I can see that it's 1 part K, 2 parts H, but I don't think it's as simple as saying 1/3 of it is potassium?

This question isn't complete. Because there is more than one way to look at it. On an atomic level, what is left is indeed 1 part potassium and 2 parts hydrogen. But, on a mass level, the potassium atom is going to much more massive than the hydrogen atoms. So, really, the question as asked is incomplete.

That said, KH2 (3+) isn't a compound, either. The phosphate ion has an ionic charge of -3. So, it needs a total of +3 ions to it in order to be charge neutral. In this case, it picks up one potassium ion (K+) and two hydrogen ions (2 H+). The KH2 isn't all together on one side, they will actually be distributed about the PO4(-3) compound pretty evenly.

Look at how the 3 H+ ions in the pictures on this wikipedia page are distributed: http/en.wikipedia.org/wiki/Phosphate

 

[Schmill]

Thanks for your reply Bignose, I shall be reading on the link you posted.

I'm not really sure how to fully qualify the question, as I am just going from information that I am picking up as I go.

On the website that I linked to in the OP it has the following information:

Percentage of compound:
--------------------------------------------------------------------------------
K2SO4 - Potassium Sulfate
- K - Potassium 44.9%
- SO4 - Sulfate 55.1%
--------------------------------------------------------------------------------
KNO3 - Potassium Nitrate
- K - Potassium 38.7%
- NO3 - Nitrate 61.3%
--------------------------------------------------------------------------------
KCl - Potassium Chloride
- K - Potassium 52.4%
- Cl - Chloride 47.6%
--------------------------------------------------------------------------------
MgSO4+7H2O - Magnesium Sulfate (Epsom Salt )
- Mg - Magnesium 9.9%
- SO4 - Sulfate 39.0%
- Other - water 51.1%
--------------------------------------------------------------------------------
KH2PO4
- PO4 - Phosphate 69.8%
- KH2 30.2%
--------------------------------------------------------------------------------

It was this info I have been using to know that if for instance I put 10g of KNO3 into my tank, I am effectively dosing 3.87g of Potassium, and 6.13g of Nitrate.
It was when I got to the KH2PO4 that I get confused, as although it is telling me that if I put in 10g I am effectively putting in 6.98g of Phosphate, I know that of the 3.02g left some of it is effectively Potassium, but I don't know how much, is it fair to assume all of it?

 

[OohFeeshy]

http/en.wikipedia.org/wiki/Monopotassium_phosphate

It appears to be, effectively, a phosphate group with a couple of extra hydrogen atoms and a potassium. You won't get 'KH2', the potassium isn't bonded to the hydrogens and won't ever be. Presumably in water it would dissociate to give some H+ ions and a potassium ion.

 

[aaronnorth]

This should answer your question: http/www.convertunits.com/molarmass/KH2PO4

something i can tell you is that the majority of K+ comes from the KNO3, only small amunts come from the potassium phosphate.

 

[Schmill]

Many thanks for the link Aaron.

So from the original site above I had:

Percentage of compound:
--------------------------------------------------------------------------------
KNO3 - Potassium Nitrate
- K - Potassium 38.7%
- NO3 - Nitrate 61.3%
--------------------------------------------------------------------------------
KH2PO4
- PO4 - Phosphate 69.8%
- KH2 30.2%
--------------------------------------------------------------------------------

but from the site Aaron linked to I have the following:

Potassium Nitrate (KNO3)

Nitrogen (N)
Atomic Mass: 14.0067
Number of Atoms: 1
Mass Percent: 13.854%

Oxygen (O)
Atomic Mass: 15.9994
Number of Atoms: 3
Mass Percent: 47.474%

Potassium (K)
Atomic Mass: 39.0983
Number of Atoms: 1
Mass Percent: 38.672%


Potassium Diphosphate (KH2PO4)

Hydrogen (H)
Atomic Mass: 1.00794
Number of Atoms: 2
Mass Percent: 1.481%

Oxygen (O)
Atomic Mass: 15.9994
Number of Atoms:4
Mass Percent: 47.027%

Phosphorus (P)
Atomic Mass: 30.973761
Number of Atoms:1
Mass Percent: 22.761%

Potassium (K)
Atomic Mass: 39.0983
Number of Atoms: 1
Mass Percent: 28.731%

So tackling the KN03 first, the Potassium % seems to agree between the formulas (38.67%), and allowing for the fact that Nitrate is defined as 1:3 of Nitrogen:Oxygen, combining the nitrogen and oxygen mass percentages gives 61.328% which is close enough to the first website for me to be happy

Tackling the KH2PO4, the first thing that struck me is the fact that the second site calls this "Potassium Diphosphate" whereas the first site, (and most 'outlets'), seem to call the same chemical name, "Mono Potassium Phosphate".
'Di' generally means "twice / double/ two", so I take "Potassium Diphosphate" to mean "1 Potassium, 2 Phosphate".
'Mono' I would take to mean "single", which would make it redundant in the name "Monopotassium Phosphate", so I can only assume that it's a way of saying that the first component is half the second, which would agree with the other name.
From this we are looking firstly for Phosphate, which is 1:4 Phosphorus:Oxygen so combining those percentages gives me 22.761 + 47.027 = 69.788%. Close enough to the first site's 69.8% for me to be happy again
So, to finally answer my own question, of what remains, 28.731% is Potassium, and the remaining percentage is Hydrogen.

Which is interesting to me because a lot of the time it is stated that the KN03 is used for the nitrate and the potassium, and the KH2PO4 is used primarily for Phosphate.
However the above would seem to show that although the KH2PO4 does obviously have mainly Phosphate in it, it also has a farily significant 28.7% of Potassium.

Not sure if this will help anyone else, or even if my ramblings will make sense to anyone else, but for me it has been a great help, so thank you to all who have posted links and info

(If anyone can clear up the naming difference between "Monopotassium Phosphate" and "Potassium Diphosphate" then I'd be interested too )

Thanks!

 

[aaronnorth]

Mono - K2PO4
di - KH2PO4

notice the extra hydrogen atoms in the second one - well thats the differemce. It is actaully Potassium DiHydrogen Phosphate

 

[Schmill]

Cheers Aaron, by that reconing then I take it that Aqua Essentials are using the wrong name, (and that what they are selling is KH2PO4, and NOT Mono Potassium Phosphate?

AquaEssentials KH2PO4


Actually, looking the AquaEssentials 'model number', that say K2PO4... so I guess THEY are the only ones that can actually say which it is that they are selling?

 

[aaronnorth]

It doesnt make a difference so i wouldnt be too worried - any form of soluable phosphate is fine to use.

Or are you wanting to know so you know how much K & PO4 you are dosing?

 

[Schmill]

Yeah, thats pretty much it Aaron, I know I have probably taken things too far, but I've taken each fert that I am dosing, and broken it down into it's component parts, so that I can tell exactly how much of each of the 'required' components that I am dosing.

KH2PO4 would give me 69.79% Phosphate, and 28.73% Potassium
K2PO4 would be giving me 54.84% Phosphate, and 45.16% Potassium, (which would also seem to make it BETTER for Potassium dosing than just relying on the KNO3)

So thats where I am at at the moment. I think a quick call to AE is in order

EDIT Working hours are Monday to Friday only. For now based on thier own code for it being K2PO4, and the name on the site being Mono Potassium Phosphate, I'll assume for now that is what I have, and they have just made a naming error on their site

 

[Schmill]

For those interested, a nice in depth response from AE:

Hi,
I am enquiring about the following dry powder fertaliser on your site:

Mono Potassium Phosphate (KH2P04)
Model: K2P04
Manufactured by: Aqua Essentials
http/www.aquaessentials.co.uk/index.php?...roducts_id=1557

Please can you confirm for me whether this is actually Mono Potassium Phosphate (K2PO4) as the name & 'model number' would seem to indicate, or whether it is actually Potassium Diphosphate (KH2PO4) as indicated by the chemical compound.

Many thanks

Hi

It's mono potassium sulphate

So a short response, but it seems that it is K2PO4 that they are supplying, not KH2PO4. (Either that or they just wanted rid of me - lol)

 

[Bignose]

Hi

It's mono potassium sulphate

So a short response, but it seems that it is K2PO4 that they are supplying, not KH2PO4. (Either that or they just wanted rid of me - lol)

Well, no. K2PO4 isn't even a valid compound. The charges aren't balances. PO4 has a charge of -3. That means that there has to be +3 in balancing charges, because the grand total of all the charges has to be zero. Each K has a charge of +1. Only having 2 K is not enough, because the sum of the charges is -1. That's where the H comes in on K2HPO4, because H also has a charge of +1.

Mono potassium sulphate would be KHSO4. SO4 is an ion with a charge of -2, and each of the K and H provide +1. And "sulphate" is the term for SO4, where as phosphate is PO4.

 

[Schmill]

SO what the heck are they selling???

This was the link to K2PO4 that I was looking at: [URL="http/www.convertunits.com/molarmass/K2PO4"]http/www.convertunits.com/molarmass/K2PO4[/URL]

So are yousaying bignose, then that they are going to be selling KH2PO4 as a fertaliser, whether thats what they think it is or not?

I've got to make up some more fertalisers tomorrow, and obviously depending on what compound it is, effects how much Potassium, and phosphate are in it.

Their answer of it being Mono Potassium Sulphate seems strange as then it is completely different to what they say it is!
IE I bought the compound mainly for the Phosphate part of it, but if that part is sulphate then that is no good.