Re: [APD] Calcium compounds

["Jerry Smith" <jerrytheplater at hotmail_com>]

Charles:

Thanks for including the phosphates. I didn't think of them when I gave the 
example. I checked all the phosphates in the CRC Handbook. Even though I use 
chemistry in my work, I am not a chemist and really don't know how to 
predict which phosphate compound would form when adding a calcium nitrate 
solution to a planted tank fertilized with phosphate. I know it has 
something to do with Eo values but I still don't understand.

I use Mono potassium phosphate in my EI mix. KH2PO4. I see Calcium 
orthophosphate, Mono  in the Handbook: Ca(H2PO4)2-H2O  I suspect this is the 
compound which would primarily form as the bulk of the KH2PO2 would 
dissociate into K+ and H2PO4- first. It would be followed by the H2PO4- 
dissociating into H+ and HPO4-- and so on. Now my head is starting to swim. 
The Ca++ would combine with two H2PO4- ions and most of it would precipitate 
except for the 1.8 gm/100 cc @ 30 C which dissolves.

Anyway, to complete the Calcium list:

Calcium hypophosphate Ca2P2O6-2H2O   Insoluble
Calcium metaphosphate Ca(PO3)2   Insoluble
Calcium orthophosphate, di- (secondary) Natural brushite CaHPO4-2H2O  0.0316 
gm/100 cc @ 38 C
Calcium orthophosphate, mono- (primary) Ca(H2PO4)2-H2O  1.8 gm/100 cc @ 30 C
Calcium orthophosphate, tri- (tertiary) Natural whitlockite  Ca3(PO4)2 0.002 
gm/100 cc @ ? C
Calcium pyrophosphate Ca2P2O7  Insoluble
Calcium pyrophosphate, pentahydrate  Ca2P2O7-5H2O  slightly soluble

Jerry Smith



>Date: Tue, 18 Jul 2006 18:52:04 -0500
>From: Charles & Sue Harrison <csharrison at inkmaker_net>
>Subject: [APD] Calcium compounds
>
>I think you left our Calcium Phosphate  Ca3(PO4)2
>
>Not very soluble and when the Phosphates are mixed with Calcium compounds . 
>. .
>
>Charles Harrison in St Louis
>Charles & Sue Harrison


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