Phosphorus acids Hydrogen phosphates

Phosphoric acid made by the wet process, in which phosphate rock is treated with sulfuric acid, is highly inert toward lead in any concentration for temperatures up to 150°C, However, in the dry process, where hydrogen phosphate (H3PO4) is made directly from phosphorus or phosphorus pentoxide (P2OS), a chemical reaction with lead occurs. 

Plants are highly sensitive to soil acidity because many equilibria involving plant nutrients are affected by pH. Phosphorus is a primary example. This essential element for plant growth occurs in soils mainly as phosphates, which are subject to phosphate-hydrogen phosphate equilibria. Consequently, phosphorus is... 

C21-0082. Calcium dihydrogen phosphate is a common phosphoras fertilizer that is made by treating fluoroapatite with phosphoric acid. Hydrogen fluoride is a by-product of the synthesis. Write a balanced equation for the production of this fertilizer and calculate the mass percent of phosphorus in the fertilizer. 

Phosphorus acid is a moderately strong dibasic acid. It reacts with alkalies forming acid phosphites and normal phosphites. Thus, reaction with sodium hydroxide gives sodium dihydrogen phosphite and disodium hydrogen phosphite, but not sodium phosphate, Na3P04. 

Tricalcium Phosphate. CarlPOjij. white solid, insoluble in water, reactive with silicon oxide and carbon ai eleciric furnace temperaiure yielding phosphorus vapor reactive with H1SO4 to form, according tn the proportions used, phosphoric acid, or dicalcium hydrogen phosphate, CaHPOa, white solid, insoluble or calcium dihydrogen phosphate, Cal 1L POrb- H O. white solid, soluble. pK,p = 28.70. See also Apatite. 

Phosphoric acid is not affected by the ordinary reducing agents in solution, including nascent hydrogen (cp. phosphorous acid, p. 148). The reduction of phosphorus pentoxide and phosphates by carbon at high temperatures has been discussed on p. 157. 

Phosphate consists of a central atom of phosphorus, four atoms of oxygen, and zero to three atoms of hydrogen. Phosphate resonates among several forms. A few forms of phosphate are shown in Figure 10.35A. Phosphate occurs in equilibrium with H P04, HiPO , HPOJ, and PO (Figure 10.35B). The predominant form at neutral pH is Hl . The fully protonated form, which is the predominant form in an environment of low pH, is phosphoric acid (H3F04). 

Hydrolyzable phosphates and organic phosphorus compounds are not detected in the course of the determination of hydrogen phosphate ions under the conditions described here (no acid hydrolysis). In order to ensure complete differentiation of the individual phosphate and phosphorus compounds in the water sample, determination of the orthophosphate must be conducted at the latest 3 hours after taking the sample. Longer storage times may lead to shifts in the ratios between the individual forms of bonds as a result of precipitation or gradual hydrolysis. 

Organic phosphorus compounds are converted to hydrogen phosphate ions by wet-ashing with sulphuric acid and hydrogen peroxide. The hydrolyzable... 

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