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Dicalcium phosphate is the calcium phosphate with the formula CaHPO 4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO 4 2– anion involves the removal of two protons from phosphoric acid, H 3 PO 4.
Its solubility product K sp of 5.02 × 10 −6 at 25 °C, [1] its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction: Ca(OH) 2 → Ca 2+ + 2 OH −. The solubility is affected by the common-ion effect. Its solubility drastically decreases upon addition of hydroxide or calcium sources.
These materials contain Ca 2+ combined with the polyphosphates, such as P 2 O 4− 7 and triphosphate P 3 O 5− 10: Dicalcium diphosphate (CAS#7790-76-3]: Ca 2 P 2 O 7; Calcium triphosphate (CAS# 26158-70-3): Ca 5 (P 3 O 10) 2
(In contrast, arsenous acid's major tautomer is the trihydroxy form.) IUPAC recommends that the trihydroxy form P(OH) 3 be called phosphorous acid, and the dihydroxy form HP(O)(OH) 2 phosphonic acid. [3] Only the reduced phosphorus compounds are spelled with an "-ous" ending. P III (OH) 3 ⇌ HP V (O)(OH) 2 K = 10 10.3 (25°C, aqueous) [4]
The general formula of a phosphoric acid is H n+2−2x P n O 3n+1−x, where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and n + 2 / 2 .
The molecule displays P(═O)H to P–OH tautomerism similar to that of phosphorous acid; the P(═O) form is strongly favoured. [6] HPA is usually supplied as a 50% aqueous solution and heating at low temperatures (up to about 90 °C) prompts it to react with water to form phosphorous acid and hydrogen gas. H 3 PO 2 + H 2 O → H 3 PO 3 + H 2
It is a conjugate acid of phosphate [PO 4] 3-and a conjugate base of dihydrogen phosphate [H 2 PO 4] −. It is formed when a pyrophosphate anion [P 2 O 7] 4− reacts with water H 2 O by hydrolysis, which can give hydrogenphosphate: [P 2 O 7] 4− + H 2 O ⇌ 2 [HPO 4] 2−
Ca 5 (PO 4) 3 OH + 5 H 2 SO 4 → 3 H 3 PO 4 + 5 CaSO 4 + H 2 O Ca 5 (PO 4) 3 F + 5 H 2 SO 4 → 3 H 3 PO 4 + 5 CaSO 4 + HF. Calcium sulfate (gypsum, CaSO 4) is a by-product, which is removed as phosphogypsum. The hydrogen fluoride (HF) gas is streamed into a wet (water) scrubber producing hydrofluoric acid. In both cases the phosphoric acid ...