ISSN:
1572-8927
Keywords:
Ionization of phosphoric acid
;
enthalpy of dilution
;
phosphate solutions
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The enthalpies of dilution of aqueous solutions of HCl, H3PO4, NaOH, NaH2PO4, Na2HPO4 and Na3PO4 in the molality range 0.1 to 1.0 mole-kg−1 have been determined at 30°C. The relative apparent molal enthalpies φL of HCl, NaOH, NaH2PO4 and Na2HPO4 have been determined with the aid of an extended form of the Debye-Hückel limiting law. The relative apparent molal enthalpies for Na3PO4 solutions have been corrected for hydrolysis. A value of ΔH H o =9525±150 cal-mole−1 was determined for the heat of hydrolysis of PO 4 −3 . This value gives ΔH 3 o =3815±150 cal-mole−1 for the ionization of H2PO 4 − , which is in good agreement with the value of ΔH 3 o =3500±500 cal-mole−1 determined directly by Pitzer at 25°C. The relative apparent molal enthalpies for H3PO4 solutions have been corrected for ionization. A value of ΔH 1 o =−1900±150 cal-mole−1 was obtained for the heat of ionization of H3PO4 to H++H2PO 4 − . This value is in good agreement with the value of ΔH 1 o =−2031 cal-mole−1 at 30°C determined by Harned and Owen from the temperature coefficient of the equilibrium constant and ΔH 1 o =−1950±80 cal-mole−1 at 25°C determined from calorimetry by Pitzer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00645297
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