Na2HPO4" /> Na2HPO4"> Na2HPO4">
Chemical elements
    Physical Properties
    Chemical Properties
      Sodium hydride
      Sodium fluoride
      Sodium hydrogen fluoride
      Sodium chloride
      Sodium bromide
      Sodium iodide
      Sodium hypochlorite
      Sodium chlorate
      Sodium hypobromite
      Sodium bromate
      Sodium hypoiodite
      Sodium iodate
      Sodium periodates
      Sodium monoxide
      Sodium peroxide
      Sodium hydroxide
      Sodium perhydroxide
      Sodium monosulphide
      Sodium polysulphides
      Sodium hydrogen sulphide
      Sodium sulphite
      Sodium hydrogen sulphite
      Sodium potassium sulphite
      Sodium pyrosulphite
      Sodium sulphate
      Sodium hydrogen sulphate
      Sodium monopersulphate
      Sodium pyrosulphate
      Sodium persulphate
      Sodium thiosulphate
      Sodium dithionate
      Sodium trithionate
      Sodium tetrathionate
      Sodium pentathionate
      Sodium hyposulphite
      Sodium selenides
      Sodium selenite
      Sodium selenate
      Sodium sulphodiselenide
      Sodium tellurides
      Sodium tellurate
      Sodium nitride
      Sodium hydrazoate
      Sodium hydrazide
      Sodium hyponitrite
      Sodium nitrite
      Disodium nitrite
      Sodium nitrate
      Sodium phosphides
      Sodium dihydrophosphide
      Sodium hypophosphite
      Sodium phosphites
      Sodium dihydrogen phosphite
      Sodium hypophosphates
      Sodium orthophosphates
      Disodium hydrogen orthophosphate
      Sodium pyrophosphate
      Disodium dihydrogen pyrophosphate
      Sodium metaphosphate
      Sodium polyphosphate
      Sodium arsenites
      Sodium arsenates
      Sodium antimonate
      Sodium carbide
      Sodium carbonate
      Sodium hydrogen carbonate
      Sodium percarbonate
      Sodium cyanide
      Sodium thiocyanate
      Sodium silicates
      Sodium borates
    PDB 131d-1bli
    PDB 1bph-1d10
    PDB 1d11-1ej2
    PDB 1eja-1gb5
    PDB 1gb6-1goh
    PDB 1gq2-1ikp
    PDB 1ikq-1jz1
    PDB 1jz2-1kvs
    PDB 1kvt-1me8
    PDB 1mg2-1nsz
    PDB 1nta-1oyt
    PDB 1p0s-1qjs
    PDB 1qnj-1s5d
    PDB 1s5e-1tjp
    PDB 1tk6-1uxt
    PDB 1uxu-1vzq
    PDB 1w15-1xc6
    PDB 1xcu-1yf1
    PDB 1ygg-1zko
    PDB 1zkp-2afh
    PDB 2agv-2bhc
    PDB 2bhp-2cc6
    PDB 2cc7-2dec
    PDB 2deg-2ein
    PDB 2eit-2fjb
    PDB 2fld-2gg8
    PDB 2gg9-2h9j
    PDB 2h9k-2ien
    PDB 2ieo-2jih
    PDB 2jin-2omd
    PDB 2omg-2p77
    PDB 2p78-2q68
    PDB 2q69-2qz7
    PDB 2qzi-2v35
    PDB 2v3h-2vwo
    PDB 2vx4-2wig
    PDB 2wij-2x1z
    PDB 2x20-2xmk
    PDB 2xmm-2zfq
    PDB 2zfr-3a6s
    PDB 3a6t-3b1e
    PDB 3b2n-3bos
    PDB 3bov-3ccr
    PDB 3ccs-3d7r
    PDB 3d97-3e3y
    PDB 3e40-3erp
    PDB 3euw-3fgw
    PDB 3fh4-3g3r
    PDB 3g3s-3gxw
    PDB 3gyz-3hwt
    PDB 3hww-3ijp
    PDB 3imm-3k0g
    PDB 3k13-3l7x
    PDB 3l88-3max
    PDB 3mbb-3mr1
    PDB 3mty-3nu3
    PDB 3nu4-3ot1
    PDB 3ow2-3qwc
    PDB 3qx5-3tfr
    PDB 3tfs-3v6o
    PDB 3v72-4ag2
    PDB 4aga-4eae
    PDB 4ecn-4g8t
    PDB 4gdt-8icw
    PDB 8icx-9icy

Disodium hydrogen orthophosphate, Na2HPO4

Disodium hydrogen orthophosphate, Na2HPO4, is obtained in the form of dodecahydrate by neutralizing phosphoric acid with sodium carbonate. It is the ordinary sodium phosphate of commerce, and is a white, crystalline salt, its solubility at 10° C. per. 100 grams of water being 3.9 grams, and at 30° C. 24.1 grams.

Solubility of Disodium Hydrogen Orthophosphate (Shiomi)

Temperature, °C10.2625.1540.260.2399.77
Grams Na2HPO4 in 100 g. water3.5512.0254.8883.00102.15

There are three breaks in the curve: at 36.45° C., corresponding with the transition from dodecahydrate to heptahydrate; at 48° C. (probably heptahydrate to dihydrate); and at 95.2° C. (probably dihydrate to anhydrous salt). Later work has indicated the dodecahydrate to exist in two forms, α and β, their transition-temperature being 29.6° C. The transition-temperature of the α-hydrate to the heptahydrate was found to be 35.0° C. The solubilities of the two dodecahydrates were also determined.

For the density of the dodecahydrate Clarke gives 1.535, and at the temperature of liquid air Dewar gives the value 1.545. For the specific heat of the crystalline salt between -20° and 2° C. Person found 0.454, and for the fused salt between 44° and 97° C. 0.758; for the solid dodecahydrate Nernst and Lindemann give 0.3723, and for the heptahydrate 0.3230. Thomsen gives 50.04 Cal. as the heat of formation of the dihydrate from sodium hydroxide and phosphoric acid. The latent heat of fusion of the dodecahydrate at 36.1° C. is given by Person as 23.9 Cal.

For the transition-points of the dodecahydrate to the heptahydrate and of the heptahydrate to the dihydrate d'Ans and Schreiner give

Na2HPO4,12H2O(35.4° C.) Na2HPO4,7H2O(48.35° C.) Na2HPO4,2H2O.

At a pressure of 0.1 atm. Biltz gives the transition-points on the absolute scale as

Na2HPO4,12H2O(317°)→Na2HPO4,7H2O(319°)→Na2HPO4,2H2O(346°) Na2HPO4.

The transition-point of the dodecahydrate into the heptahydrate is given by Person as 36.4° C., Baur 36.6° C., and Tilden 35° C.; and the transition-point into the anhydrous salt by Muller as 43.5° C.

When heated, disodium hydrogen phosphate gives up its water of crystallization, and then decomposes, forming sodium pyrophosphate.

Other investigations include the refraction constants, and the dissociation-pressure of the water of crystallization of the dodecahydrate at the transition-point; and such properties of solutions as density, specific heat, boiling-point, vapour-pressure, molecular depression of the freezing-point, electric conductivity, and hydrolytic dissociation.

Treatment of disodium hydrogen orthophosphate with phosphoric acid converts it into sodium dihydrogen orthophosphate, NaH2PO4, which crystallizes as monohydrate and dihydrate. For the density of the monohydrate Schiff gives 2.040, and for that of the dihydrate Dufet gives 1.9096. On heating, the salt loses its water of crystallization at 100° C., and at 200° C. is converted by further dehydration into disodium dihydrogen pyrophosphate, Na2H2P2O7, and at a higher temperature this substance is transformed into sodium metaphosphate, NaPO3. At 180° C. transformation into the pyrophosphate is very slow, about 178 hours being required for complete conversion.

At 0° C. 100 grams of water dissolve 59.9 grams, and at 18° C. 84.6 grams of the salt, yielding an acid solution. For the heat of formation from the elements Berthelot gives 355.0 Cal.; from the interaction of phosphoric acid and sodium hydroxide he gives 14.7 Cal., and Thomsen 14.829 Cal.

Attention has also been directed to the refractivity of the salt; and to such properties of its solution as vapour-pressure, molecular depression of the freezing-point, electric conductivity, and hydrolytic dissociation.

© Copyright 2008-2012 by