Volumetric properties of disodium dihydrogen pyrophosphate aqueous solution from 283.15 to 363.15 K at 101.325 kPa

The purpose of this exploration was to determine the density and volumetric properties of the aqueous solution of Na 2 H 2 P 2 O 7 with the molality varied from 0.08706 to 0.88402 mol·kg −1 measured at temperature intervals of 5 K from 283.15 to 363.15 K at 101.325 kPa using Anton Paar Digital vibrating-tube densimeter. The thermal expansion coefficient ( α ), apparent molar volume ( V Φ ), expansibility ( ϕ E ${\varphi }_E$ ), and partial molar volume ( V B ) of Na 2 H 2 P 2 O 7 (aq) against temperature and molality have been evaluated from density data. On the basis of Pitzer ion-interaction apparent molar volume theory, the Pitzer single-salt parameters ( β M , X 0 v ${\beta }_{\text{M},\text{X}}^{\left(0\right)v}$ , β M , X 1 v ${\beta }_{\text{M},\text{X}}^{\left(1\right)v}$ , β M , X 2 v ${\beta }_{\text{M},\text{X}}^{\left(2\right)v}$ and C M , X v $C_{\text{M},\text{X}}^v$ , MX = Na 2 H 2 P 2 O 7 ), and their correlation coefficients a i of the temperature-dependence formula f ( i , p , T ) =  a 1  +  a 2 ln( T /298.15) +  a 3 ( T − 298.15) +  a 4 /(620 – T ) +  a 5 /( T − 227) for Na 2 H 2 P 2 O 7 were obtained for the first time. It was revealed that predicted apparent molar volumes agreed well with the experimental values indicating the single salt parameters and the temperature-dependent formula are reliable.